記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

Reducing cadmium (Cd) accumulation in rice grain is an important issue for human health. The aim of this study was to manipulate both expression and tissue localization of OsHMA3, a tonoplast-localized Cd transporter, in the roots by expressing it under the control of the OsHMA2 promoter, which shows high expression in different organs including roots, nodes, and shoots. In two independent transgenic lines, the expression of OsHMA3 was significantly enhanced in all organs compared with non-transgenic rice. Furthermore, OsHMA3 protein was detected in the root pericycle cells and phloem region of both the diffuse vascular bundle and the enlarged vascular bundle of the nodes. At the vegetative stage, the Cd concentration in the shoots and xylem sap of the transgenic rice was significantly decreased, but that of the whole roots and root cell sap was increased. At the reproductive stage, the concentration of Cd, but not other essential metals, in the brown rice of transgenic lines was decreased to less than one-tenth that of the non-transgenic rice. These results indicate that expression of OsHMA3 under the control of the OsHMA2 promoter can effectively reduce Cd accumulation in rice grain through sequestering more Cd into the vacuoles of various tissues.

DOI： 10.1093/jxb/ery107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

Plant NRT2 nitrate transporters commonly require a partner protein, NAR2, for transporting nitrate at low concentrations, but their role in plants is not well understood. In this study, we characterized the gene for one of these transporters in the rice genome, OsNRT2.4, in terms of its activity and roles in rice grown in environments with different N supply. In Xenopus oocytes, OsNRT2.4 alone without OsNAR2 co-expression facilitated nitrate uptake showing biphasic kinetics at a wide concentration range, with high- and low-affinity K M values of 0.15 and 4 mM, respectively. OsNRT2.4 did not have nitrate efflux or IAA influx activity. In rice roots, OsNRT2.4 was expressed mainly in the base of lateral root primordia. Knockout of OsNRT2.4 decreased lateral root number and length, and the total N uptake per plant at both 0.25 and 2.5 mM NO 3 - ' levels. In the shoots, OsNRT2.4 was expressed mainly in vascular tissues, and its knockout decreased the growth and NO 3 - ' -N distribution. Knockout of OsNRT2.4, however, did not affect rice growth and N uptake under conditions without N or with only NH 4 + supply. We conclude that OsNRT2.4 functions as a dual-affinity nitrate transporter and is required for nitrate-regulated root and shoot growth of rice.

DOI： 10.1093/jxb/erx486

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Society of Plant Biologists  

Boron is especially required for the growth of meristem and reproductive organs, but the molecular mechanisms underlying the preferential distribution of B to these developing tissues are poorly understood. Here, we show evidence that a member of nodulin 26-like intrinsic protein (NIP), OsNIP3
1, is involved in this preferential distribution in rice (Oryza sativa). OsNIP3
1 was highly expressed in the nodes and its expression was up-regulated by B deficiency, but down-regulated by high B. OsNIP3
1 was polarly localized at the xylem parenchyma cells of enlarged vascular bundles of nodes facing toward the xylem vessels. Furthermore, this protein was rapidly degraded within a few hours in response to high B. Knockout of this gene hardly affected the uptake and root-to-shoot translocation of B, but altered B distribution in different organs in the above-ground parts, decreased distribution of B to the new leaves, and increased distribution to the old leaves. These results indicate that OsNIP3
1 located in the nodes is involved in the preferential distribution of B to the developing tissues by unloading B from the xylem in rice and that it is regulated at both transcriptional and protein level in response to external B level.

DOI： 10.1104/pp.17.01641

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掲載種別：研究論文（学術雑誌）  

© 2018 Taylor & Francis Group, LLC. Rice (Oryza sativa L) is one of the most Mn-tolerant crops that can grow in submerged paddy fields, where the Mn concentration in soil solution is very high due to reduction. Although a large part of Mn is transferred from the roots to the shoot in rice, the roots are constantly exposed to high Mn concentrations in submerged paddies. Thus, mechanisms for preventing Mn overaccumulation in the cytoplasm of root cells are necessary. Recently, we showed that two cation diffusion facilitators, MTP8.1 and MTP8.2, play a crucial role in Mn tolerance in rice roots by sequestering Mn in vacuoles. Moreover, we observed that disruption of MTP8.1 and MTP8.2 resulted in reduced Mn accumulation under excess Mn. In the present study, we examined the effects of disruption of MTP8.1 and MTP8.2 on Mn uptake and determined that this phenotype is caused by a rapid and significant reduction of Mn uptake in response to excess Mn. Previously, we showed that Mn export from root cells through MTP9 was promoted by high Mn. Together, these findings suggest that optimal Mn concentration in rice roots is maintained by reduced uptake, vacuolar sequestration, and extrusion by cation diffusion facilitators.

DOI： 10.1080/15592324.2017.1422466

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DOI： 10.1111/nph.15252

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Buckwheat (Fagopyrum esculentum) shows high tolerance to aluminum (Al) toxicity, but the molecular mechanisms responsible for this high Al tolerance are still poorly understood. Here, we investigated the involvement of two MATE (multi-drug and toxic compound extrusion) genes in Al tolerance. Both FeMATE1 and FeMATE2 showed efflux transport activity for citrate, but not for oxalate when expressed in Xenopus oocytes. A transient assay with buckwheat leaf protoplasts using green fluorescent protein (GFP) fusion showed that FeMATE1 was mainly localized to the plasma membrane, whereas FeMATE2 was localized to the trans-Golgi and Golgi. The expression of FeMATE1 was induced by Al only in the roots, but that of FeMATE2 was up-regulated in both the roots and leaves. Furthermore, the expression of both genes only responded to Al toxicity, but not to other stresses including low pH, cadmium (Cd) and lanthanum (La). Heterologous expression of FeMATE1 or FeMATE2 in the Arabidopsis mutant atmate partially rescued its Al tolerance. Expression of FeMATE1 also partially recovered the Al-induced secretion of citrate in the transgenic lines, whereas expression of FeMATE2 did not complement the citrate secretion. Further physiological analysis showed that buckwheat roots also secreted citrate in addition to oxalate in response to Al in a dose-responsive manner. Taken together, our results indicate that FeMATE1 is involved in the Al-activated citrate secretion in the roots, while FeMATE2 is probably responsible for transporting citrate into the Golgi system for the internal detoxification of Al in the roots and leaves of buckwheat.

DOI： 10.1093/pcp/pcx152

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記述言語：英語   出版者・発行元：CURRENT BIOLOGY LTD  

Mineral elements taken up by the roots will be delivered to different organs and tissues depending on their requirements. In Poaceae, this selective distribution is mainly mediated in the nodes, which have highly developed and fully organized vascular systems. Inter-vascular transfer of mineral elements from enlarged vascular bundles to diffuse vascular bundles is required for their preferential distribution to developing tissues and reproductive organs. A number of transporters involved in this inter-vascular transfer processes have been identified mainly in rice. They are localized at the different cell layers and form an efficient machinery within the node. Furthermore, some these transporters show rapid response to the environmental changes of mineral elements at the protein level. In addition to the node-based transporters, distinct nodal structures including enlarged xylem area, folded plasma membrane of xylem transfer cells and presence of an apoplastic barrier are also required for the efficient inter-vascular transfer. Manipulation of node-based transporters will provide a novel breeding target to improve nutrient use efficiency, productivity, nutritional value and safety in cereal crops.

DOI： 10.1016/j.pbi.2017.05.002

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掲載種別：研究論文（学術雑誌）  

© The Author 2017. Manganese (Mn) cation diffusion facilitators (Mn-CDFs) play important roles in the Mn homeostasis of plants. In rice, the tonoplast-localized Mn-CDF metal tolerance protein 8.1 (MTP8.1) is involved in Mn detoxification in the shoots. This study functionally characterized the Mn-CDF MTP8.2 and determined its contribution to Mn tolerance. MTP8.2 was found to share 68% identity with MTP8.1 and was expressed in both the shoots and roots, but its transcription level was lower than that of MTP8.1. Transient expression of the MTP8.2:green fluorescent protein (GFP) fusion protein and immunoblotting studies indicated that MTP8.2 was also localized to the tonoplast. MTP8.2 expression in yeast conferred tolerance to Mn but not to Fe, Zn, Co, Ni or Cd. MTP8.2 knockdown caused further growth reduction of shoots and roots in the mtp8.1 mutant, which already exhibits stunted growth under conditions of excess Mn. In the presence of high Mn, the MTP8.2 knockdown lines of the mtp8.1 mutant showed lower root Mn concentrations, as well as lower root:total Mn ratios, than those of wild-type rice and the mtp8.1 mutant. These findings indicate that MTP8.2 mediates Mn tolerance along with MTP8.1 through the sequestration of Mn into the shoot and root vacuoles.

DOI： 10.1093/pcp/pcx082

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Silicon (Si) alleviates cadmium (Cd) toxicity and accumulation in a number of plant species, but the exact molecular mechanisms responsible for this effect are still poorly understood. Here, we investigated the effect of Si on Cd toxicity and accumulation in rice (Oryza sativa) by using two mutants (lsi1 and lsi2) defective in Si uptake and their wild types (WTs). Root elongation was decreased with increasing external Cd concentrations in both WTs and mutants, but Si did not show an alleviative effect on Cd toxicity in all lines. By contrast, the Cd concentration in both the shoots and roots was decreased by Si in the WTs, but not in the mutants. Furthermore, Si supply resulted in a decreased Cd concentration in the root cell sap and xylem sap in the WTs, but not in the mutants. Pre-treatment with Si also decreased Cd accumulation in the WTs, but not in the mutants. Silicon slightly decreased Cd accumulation in the cell wall of the roots. The expression level of OsNramp5 and OsHMA2 was down-regulated by Si in the WTs, but not in the mutants. These results indicate that the Si-decreased Cd accumulation was caused by down-regulating transporter genes involved in Cd uptake and translocation in rice.

DOI： 10.1093/jxb/erx364

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

Buckwheat (Fagopyrum esculentum Moench) is able to detoxify high aluminium (Al) internally by sequestering it to the vacuoles in the leaves; however, the molecular mechanisms underlying this sequestration are unknown.
We performed proteomic analysis with the leaf tonoplast-rich fraction and identified two half-size ABC transporters; FeASL1.1 and FeALS1.2. We investigated the gene expression patterns and subcellular localization. To demonstrate their physiological role, we expressed FeALS1.1 or FeALS1.2 in the Arabidopsis atals1 mutant under the control of AtALS1 promoter.
FeALS1.1 expression was upregulated by Al in both the leaves and the roots, and its expression level in the roots was six times higher than its homologous gene (AtALS1) of Arabidopsis. FeALS1.2 expression, however, was not affected by Al but showed a 39 times higher expression level than AtALS1 in the leaves. When FeALS1.1 or FeALS1.2 was expressed in atals1, both of them recovered their Al tolerance through altering the subcellular localization of Al in root cells.
Taken together, our results indicate that FeALS1.1 and FeALS1.2 are involved in the internal detoxification of Al in the roots and leaves, respectively, by sequestering Al into the vacuoles. Their high expression is probably required for high Al tolerance in buckwheat.

DOI： 10.1111/nph.14648

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

Salt tolerance quantitative trait loci analysis of rice has revealed that the SKC1 locus, which is involved in a higher K+/Na+ ratio in shoots, corresponds to the OsHKT1;5 gene encoding a Na+-selective transporter. However, physiological roles of OsHKT1;5 in rice exposed to salt stress remain elusive, and no OsHKT1;5 gene disruption mutants have been characterized to date. In this study, we dissected two independent TDNA insertional OsHKT1;5 mutants. Measurements of ion contents in tissues and 22 Na+ tracer imaging experiments showed that loss-of-function of OsHKT1;5 in salt-stressed rice roots triggers massive Na+ accumulation in shoots. Salt stress-induced increases in the OsHKT1;5 transcript were observed in roots and basal stems, including basal nodes. Immuno-staining using an anti-OsHKT1;5 peptide antibody indicated that OsHKT1;5 is localized in cells adjacent to the xylem in roots. Additionally, direct introduction of 22 Na+ tracer to leaf sheaths also demonstrated the involvement of OsHKT1;5 in xylem Na+ unloading in leaf sheaths. Furthermore, OsHKT1;5 was indicated to be present in the plasma membrane and found to localize also in the phloem of diffuse vascular bundles in basal nodes. Together with the characteristic 22 Na+ allocation in the blade of the developing immature leaf in the mutants, these results suggest a novel function of OsHKT1;5 in mediating Na+ exclusion in the phloem to prevent Na+ transfer to young leaf blades. Our findings further demonstrate that the function of OsHKT1;5 is crucial over growth stages of rice, including the protection of the next generation seeds as well as of vital leaf blades under salt stress.

DOI： 10.1111/tpj.13595

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Salt stress is one of the major factors limiting rice (Oryza sativa) production globally. Although several transporters involved in salt tolerance have been identified in rice, the mechanisms regulating their transport activity are still poorly understood. Here, we show evidence that a rice Mg transporter OsMGT1 is required for salt tolerance probably by regulating transport activity of OsHKT1;5, a key transporter for the removal of Na+ from the xylem sap at the root mature zone. Knockout of OsMGT1 did not affect total Na uptake, but increased Na concentration in the shoots and xylem sap, resulting in a significant increase in salt sensitivity at low external Mg2+ concentration (20-200 mu M). However, such differences were abolished at a higher Mg2+ concentration (2 mM), although the total Na uptake was not altered. OsMGT1 was expressed in both the roots and shoots, but only that in the roots was moderately up-regulated by salt stress. Spatial expression analysis revealed that OsMGT1 was expressed in all root cells of the root tips but was highly expressed in the pericycle of root mature zone. OsMGT1 was also expressed in the phloem region of basal node, leaf blade, and sheath. When expressed in Xenopus laevis oocytes, the transport activity of OsHKT1;5 was enhanced by elevating external Mg2+ concentration. Furthermore, knockout of OsHKT1;5 in osmgt1 mutant background did not further increase its salt sensitivity. Taken together, our results suggest that Mg2+ transported by OsMGT1 in the root mature zone is required for enhancing OsHKT1;5 activity, thereby restricting Na accumulation to the shoots.

DOI： 10.1104/pp.17.00532

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：FRONTIERS MEDIA SA  

Silicon is the second most abundant element in soils and is beneficial for plant growth. Although, the localizations and polarities of rice Si transporters have been elucidated, the mechanisms that control the expression of Si transporter genes and the functional reasons for controlling expression are not well-understood. We developed a new model that simulates the dynamics of Si in the whole plant in rice by considering Si transport in the roots, distribution at the nodes, and signaling substances controlling transporter gene expression. To investigate the functional reason for the diurnal variation of the expression level, we compared investment efficiencies (the amount of Si accumulated in the upper leaf divided by the total expression level of Si transporter genes) at different model settings. The model reproduced the gradual decrease and diurnal variation of the expression level of the transporter genes observed by previous experimental studies. The results of simulation experiments showed that a considerable reduction in the expression of Si transporter genes during the night increases investment efficiency. Our study suggests that rice has a system that maximizes the investment efficiency of Si uptake.

DOI： 10.3389/10E-2017.01187

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE LONDON  

Plants only require small amounts of manganese (Mn) for healthy growth, but Mn concentrations in soil solution vary from sub-micromolar to hundreds of micromolar across the growth period. Therefore, plants must deal with large Mn concentration fluctuations, but the molecular mechanisms underlying how plants cope with low and high Mn concentrations are poorly understood. In this Opinion we discuss the role of Mn transporters in the uptake, distribution, and detoxification of Mn in response to changes in Mn concentrations through their regulation at the transcriptional and protein levels, mainly focusing on rice, an Mn-tolerant and accumulating species. We also propose mechanisms involved in the hyperaccumulation of Mn and future prospects for studying this specific trait.

DOI： 10.1016/j.tplants.2016.12.005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Investigations into the epigenetic status of individual cells within tissues can produce both epigenetic data for different cell types and positional information of the cells. Thus, these investigations are important for understanding the intra-and inter-cellular control systems of developmental and environmental responses in plants. However, a simple method to detect epigenetic modifications of individual cells in plant tissues is not yet available because detection of the modifications requires immunohistochemistry using specific antibodies. In this study, we developed a simple immunohistochemical method that does not require sectioning to investigate epigenetic modifications. This method uses a clearing system to detect methylated histones, acetylated histones, methylated DNA and/or centromeric histone H3 variants. Analyses of four dicots and five monocots indicated that this method provides a universal technique to investigate epigenetic modifications in diverse plant species.

DOI： 10.1038/srep42203

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Phosphorus is an important nutrient for crop productivity. More than 60% of the total phosphorus in cereal crops is finally allocated into the grains and is therefore removed at harvest. This removal accounts for 85% of the phosphorus fertilizers applied to the field each year(1,2). However, because humans and non-ruminants such as poultry, swine and fish cannot digest phytate, the major form of phosphorus in the grains, the excreted phosphorus causes eutrophication of waterways. A reduction in phosphorus accumulation in the grain would contribute to sustainable and environmentally friendly agriculture. Here we describe a rice transporter, SULTR-like phosphorus distribution transporter (SPDT), that controls the allocation of phosphorus to the grain. SPDT is expressed in the xylem region of both enlarged-and diffuse-vascular bundles of the nodes, and encodes a plasma-membrane-localized transporter for phosphorus. Knockout of this gene in rice (Oryza sativa) altered the distribution of phosphorus, with decreased phosphorus in the grains but increased levels in the leaves. Total phosphorus and phytate in the brown de-husked rice were 20-30% lower in the knockout lines, whereas yield, seed germination and seedling vigour were not affected. These results indicate that SPDT functions in the rice node as a switch to allocate phosphorus preferentially to the grains. This finding provides a potential strategy to reduce the removal of phosphorus from the field and lower the risk of eutrophication of waterways.

DOI： 10.1038/nature20610

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

To reduce cadmium (Cd) intake, remediation of Cd-contaminated soil and breeding crops with low Cd accumulation are important. This study aims to isolate rice mutants with altered accumulation of Cd.
We used rice seeds mutated by N-methyl-N-nitrosourea for screening. The mutant was physiologically, genetically, and molecularly characterized. Cd accumulation was compared among five rice varieties cultivated in a Cd-contaminated soil.
From 1000 lines screened, we isolated a line (TCM213) with high Cd accumulation. There was no difference in the root Cd uptake, but a higher root-to-shoot translocation of Cd was found in TCM213 compared with a common rice cultivar, T-65. The expression and sequence of OsNramp5 and OsHMA2 did not differ between TCM213 and T-65. However, several SNPs and deletion were found in the sequence of OsHMA3, although its expression and tissue localization were similar to those of T-65. Genetic analysis of an F-2 population derived from T-65 and TCM213 showed that the variation of OsHMA3 explained 72 % of variation in total Cd accumulation. TCM213 accumulated the largest Cd amount in the shoots among five Cd-accumulating varieties.
High Cd accumulation in TCM213 results from loss of function of OsHMA3, and its high Cd accumulation has potential for efficient phytoremediation of Cd-contaminated soil.

DOI： 10.1007/s11104-016-3014-y

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記述言語：英語   出版者・発行元：NATURE PUBLISHING GROUP  

DOI： 10.1038/nature21404

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

High aluminum (Al) tolerance of rice (Oryza sativa) is controlled by multiple tolerance genes, but the regulatory mechanisms underlying the differential expression of these genes are poorly understood. Here, we investigated the factors regulating the expression of OsFRDL4, a gene encoding a citrate efflux transporter involved in Al-induced citrate secretion from the roots. Analysis with chromosome segment substitution lines derived from cv Nipponbare (high OsFRDL4 expression) and cv Kasalath (low OsFRDL4 expression) revealed that the differential expression of OsFRDL4 is responsible for the quantitative trait locus for Al tolerance detected previously on chromosome 1. Comparison of the OsFRDL4 gene structure in cv Nipponbare and cv Kasalath showed that there was no difference in the position of the transcriptional start site, but a 1.2-kb insertion showing high similarity to the solo long terminal repeat of the retrotransposon was found in the promoter region of OsFRDL4 in cv Nipponbare. This insertion showed higher promoter activity and contained nine cis-acting elements for ALUMINUM RESISTANCE TRANSCRIPTION FACTOR1 (ART1). However, this insertion did not alter the spatial expression or cellular localization of OsFRDL4. Furthermore, this insertion was found in most japonica varieties but was largely absent from indica varieties or wild rice species. These results indicate that the 1.2-kb insertion in the OsFRDL4 promoter region in japonica subspecies is responsible for their higher expression level of OsFRDL4 due to the increased number of cis-acting elements of ART1. Our results also suggest that this insertion event happened at the initial stage of domestication of japonica subspecies.

DOI： 10.1104/pp.16.01214

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記述言語：英語   出版者・発行元：GENETICS SOC JAPAN  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Rice requires high silicon (Si) for its high and sustainable yield. The efficient uptake of Si in rice is mediated by two transporters OsLsi1 and OsLsi2, which function as influx and efflux transporters, respectively. Our previous studies showed that the mRNA expression levels of these transporter genes were down-regulated by Si. Herein we investigated the mechanism underlying regulation of OsLsi1 and OsLsi2 expression. There was a negative correlation between the expression level of OsLsi1 and OsLsi2 and shoot Si accumulation when the rice seedlings were exposed to different Si supply conditions. A split root experiment showed that the expression of both OsLsi1 and OsLsi2 was also downregulated in half the roots without direct Si exposure when the other half of the roots were exposed to Si. Analysis with transgenic rice carrying different lengths of OsLsi1 promoter regions fused with green fluorescent protein (GFP) as a reporter gene revealed that the region responsible for the Si response of OsLsi1 expression is present between -327 to -292 in the promoter. However, this region was not associated with the tissue and cellular localization of OsLsi1. In conclusion, the Si-induced down-regulation of Si transporter genes is controlled by shoot Si, not root Si, and the region between -327 and -292 in the OsLsi1 promoter is involved in this regulation of OsLsi1 expression in rice.

DOI： 10.1093/pcp/pcw163

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記述言語：英語  

The Natural Resistance Associated Macrophage Protein (Nramp) represents a transporter family for metal ions in all organisms. Here, we functionally characterized a member of Nramp family in barley (Hordeum vulgare), HvNramp5. This member showed different expression patterns, transport substrate specificity, and cellular localization from its close homolog in rice (Oryza sativa), OsNramp5, although HvNramp5 was also localized to the plasma membrane. HvNramp5 was mainly expressed in the roots and its expression was not affected by Cd and deficiency of Zn, Cu, and Mn, but slightly up-regulated by Fe deficiency. Spatial expression analysis showed that the expression of HvNramp5 was higher in the root tips than that in the basal root regions. Furthermore, analysis with laser microdissection revealed higher expression of HvNramp5 in the outer root cell layers. HvNramp5 showed transport activity for both Mn2+ and Cd2+, but not for Fe2+ when expressed in yeast. Immunostaining with a HvNramp5 antibody showed that this protein was localized in the root epidermal cells without polarity. Knockdown of HvNramp5 in barley resulted in a significant reduction in the seedling growth at low Mn supply, but this reduction was rescued at high Mn supply. The concentration of Mn and Cd, but not other metals including Cu, Zn, and Fe, was decreased in both the roots and shoots of knockdown lines compared with the wild-type barley. These results indicate that HvNramp5 is a transporter required for uptake of Mn and Cd, but not for Fe, and that barley has a distinct uptake system from rice.

DOI： 10.1104/pp.16.01189

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Expansins are cell wall loosening proteins, which are encoded by multigene families. However, the physiological role of most expansin genes is still poorly understood. Here, we functionally characterized an Al-inducible expansin gene, OsEXPA10, which is regulated by a C2H2-type zinc-finger transcription factor, ART1 in rice. A detailed expression analysis showed that OsEXPA10 was expressed in both the roots and shoots at a similar level, but only the expression in the roots was rapidly upregulated in response to Al. Furthermore, spatial expression analysis showed that the Al-induced expression was only found in the root tips (0-3 mm), but not in the mature root zones. The expression was neither induced by other metals including Cd and La nor by low pH. Immunostaining showed that OsEXPA10 was localized at all cells of the root tips. Knockout of OsEXPA10 resulted in a significant decrease in the cell elongation of the roots in the absence of Al. In the presence of Al, knockout of OsEXPA10 did not alter the Al sensitivity evaluated by relative root elongation, but the root cell wall of knockout lines accumulated less Al compared to those of the wild-type rice. Collectively, our results indicate that OsEXPA10 expressed in the root tips is required for the root cell elongation, but that the contribution of this gene to high Al tolerance in rice is small.

DOI： 10.1111/tpj.13237

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

OsFRDL1 expressed in the upper nodes is required for the distribution of Fe to the panicles through solubilizing Fe deposited in the apoplastic part of nodes in rice.Iron (Fe) is essential for plant growth and development, but the molecular mechanisms underlying its distribution to different organs are poorly understood. We found that OsFRDL1 (FERRIC REDUCTASE DEFECTIVE LIKE 1), a plasma membrane-localized transporter for citrate, was highly expressed in the upper nodes of rice at the reproductive growth stage. OsFRDL1 was expressed in most cells of enlarged vascular bundles, diffuse vascular bundles, and the interjacent parenchyma cell bridges of uppermost node I, as well as vascular tissues of the leaf blade, leaf sheath, peduncle, rachis, husk, and stamen. Knockout of OsFRDL1 decreased pollen viability and grain fertility when grown in a paddy field. Iron was deposited in the parenchyma cell bridges, a few of the cell layers of the parenchyma tissues outside of the bundle sheath of enlarged vascular bundles in node I in both the wild-type rice and osfrdl1 mutant, but the mutant accumulated more Fe than the wild-type rice in this area. A stem-fed experiment with stable isotope Fe-57 showed that the distribution of Fe in the anther and panicle decreased in the knockout line, but that in the flag leaf it increased compared with the wild-type rice. Taken together, our results show that OsFRDL1 expressed in the upper nodes is required for the distribution of Fe in the panicles through solubilizing Fe deposited in the apoplastic part of nodes in rice.

DOI： 10.1093/jxb/erw314

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Rice is a major source of calories and mineral nutrients for over half the world's human population. However, little is known in rice about the genetic basis of variation in accumulation of copper (Cu), an essential but potentially toxic nutrient. Here we identify OsHMA4 as the likely causal gene of a quantitative trait locus controlling Cu accumulation in rice grain. We provide evidence that OsHMA4 functions to sequester Cu into root vacuoles, limiting Cu accumulation in the grain. The difference in grain Cu accumulation is most likely attributed to a single amino acid substitution that leads to different OsHMA4 transport activity. The allele associated with low grain Cu was found in 67 of the 1,367 rice accessions investigated. Identification of natural allelic variation in OsHMA4 may facilitate the development of rice varieties with grain Cu concentrations tuned to both the concentration of Cu in the soil and dietary needs.

DOI： 10.1038/ncomms12138

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

One of the most important roles of plant roots is to take up essential mineral nutrients from the soil for use in plant growth and development. The uptake of mineral elements is mediated by various transporters belonging to different transporter families. Here we reviewed transporters for the uptake of macronutrients and micronutrients identified in rice, an important staple food for half of the world's population. Rice roots are characterized by having two Casparian strips on the exodermis and endodermis and by the formation of aerenchyma in the mature root zone. This distinct anatomical structure dictates that a pair of influx and efflux transporters at both the exodermis and endodermis is required for the radial transport of a mineral element from the soil solution to the stele. Some transporters showing polar localization at the distal and proximal sides of the exodermis and endodermis have been identified for silicon and manganese, forming an efficient uptake system. However, transporters for the uptake of most mineral elements remain to be identified.

DOI： 10.1093/jxb/erw060

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

The stomatal apparatus consists of a pair of guard cells and regulates gas exchange between the leaf and atmosphere. In guard cells, blue light (BL) activates H+-ATPase in the plasma membrane through the phosphorylation of its penultimate threonine, mediating stomatal opening. Although this regulation is thought to be widely adopted among kidney-shaped guard cells in dicots, the molecular basis underlying that of dumbbell-shaped guard cells in monocots remains unclear. Here, we show that H+-ATPases are involved in the regulation of dumbbell-shaped guard cells. Stomatal opening of rice was promoted by the H+-ATPase activator fusicoccin and by BL, and the latter was suppressed by the H+-ATPase inhibitor vanadate. Using H+-ATPase antibodies, we showed the presence of phosphoregulation of the penultimate threonine in Oryza sativa H+-ATPases (OSAs) and localization of OSAs in the plasma membrane of guard cells. Interestingly, we identified one H+-ATPase isoform, OSA7, that is preferentially expressed among the OSA genes in guard cells, and found that loss of function of OSA7 resulted in partial insensitivity to BL. We conclude that H+-ATPase is involved in BL-induced stomatal opening of dumbbell-shaped guard cells in monocotyledon species.

DOI： 10.1093/pcp/pcw070

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Buckwheat (Fagopyrum esculentum Moench) is able to detoxify aluminum (Al) both externally and internally, but the molecular mechanisms underlying its high Al tolerance are not understood. We functionally characterized a gene (FeIREG1) belonging to IRON REGULATED/ferroportin in buckwheat, which showed high expression in our previous genome-wide transcriptome analysis. FeIREG1 was mainly expressed in the roots, and its expression was up-regulated by Al, but not by other metals and low pH. Furthermore, in contrast to AtIREG1 and AtIREG2 in Arabidopsis, the expression of FeIREG1 was not induced by Fe deficiency. Spatial expression analysis showed that the Al-induced expression of FeIREG1 was found in the root tips and higher expression was detected in the outer layers of this part. Immunostaining also showed that FeIREG1 was localized at the outer cell layers in the root tip. A FeIREG1-green fluorescent protein (GFP) fusion protein was localized to the tonoplast when transiently expressed in onion epidermal cells. Overexpression of FeIREG1 in Arabidopsis resulted in increased Al tolerance, but did not alter the tolerance to Cd, Co and Fe. The tolerance to Ni was slightly enhanced in the overexpression lines. Mineral analysis showed that the accumulation of total root Al and other essential mineral elements was hardly altered in the overexpression lines. Taken together, our results suggest that FeIREG1 localized at the tonoplast plays an important role in internal Al detoxification by sequestering Al into the root vacuoles in buckwheat.

DOI： 10.1093/pcp/pcw065

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) is characterized by having fibrous root systems; however, the molecular mechanisms underlying the root development are not fully understood. Here, we isolated a rice mutant with short roots and found that the mutant had a decreased cell size of the roots and shoots compared with wild-type rice. Map-based cloning combined with whole-genome sequencing revealed that a single nucleotide mutation occurred in a gene, which encodes a putative cation-chloride cotransporter (OsCCC1). Introduction of OsCCC1 cDNA into the mutant rescued the mutant growth, indicating that growth defects of both the roots and shoots are caused by loss of function of OsCCC1. Physiological analysis showed that the mutant had a lower concentration of Cl- and K+ and lower osmolality in the root cell sap than the wild type at all KCl supply conditions tested; however, the mutant only showed a lower Na+ concentration at high external Na+. Expression of OsCCC1 in yeast increased accumulation of K+, Na+, and Cl-. The expression of OsCCC1 was found in both the roots and shoots, although higher expression was found in the root tips. Furthermore, the expression in the roots did not respond to different Na+, K+, and Cl- supply. OsCCC1 was expressed in all cells of the roots, leaf, and basal node. Immunoblot analysis revealed that OsCCC1 was mainly localized to the plasma membrane. These results suggest that OsCCC1 is involved in the cell elongation by regulating ion (Cl-, K+, and Na+) homeostasis to maintain cellular osmotic potential.

DOI： 10.1104/pp.16.00017

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

The multidrug and toxic compound extrusion (MATE) transporters represent a large transporter family in plants, but the role of most genes in this family has not been examined. We functionally characterized a MATE family member, OsFRDL2, in rice (Oryza sativa). OsFRDL2 showed an efflux transport activity for citrate when it was expressed in both Xenopus oocytes and cultured tobacco cells. OsFRDL2 was mainly expressed in the roots and its expression was not induced by iron (Fe) deficiency, but it was rapidly up-regulated by aluminum (Al). Furthermore, the expression of OsFRDL2 was regulated by ART1, a C2H2-type zinc-finger transcription factor for Al tolerance. OsFRDL2 protein was localized at unidentified vesicles in the cytosol, but not co-localized with either mitochondria or peroxisomes when expressed in both onion epidermal cells and cultured tobacco cells. Knockout of OsFRDL2 decreased Al-induced secretion of citrate from the roots, but did not affect the internal citrate concentration. The Al-induced inhibition of root elongation was similar between the OsFRDL2 knockout line and its wild-type rice. Knockout of OsFRDL2 did not affect the translocation of Fe from the roots to the shoots. A double mutant between osfrdl2 and osfrdl4 or osfrdl1 did not further decrease the Al-induced citrate secretion and Fe translocation compared with the single mutant. Collectively, our results indicate that although OsFRDL2 is involved in the Al-induced secretion of citrate, its contribution to high Al tolerance is relatively small in rice.

DOI： 10.1093/pcp/pcw026

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Silicon (Si) is known to alleviate manganese (Mn) toxicity in a number of plant species; however, the mechanisms responsible for this effect are poorly understood. Here, we investigated the interaction between Si and Mn in rice (Oryza sativa) by using a mutant defective in Si uptake. Silicon alleviated Mn toxicity in the wild-type (WT) rice, but not in the mutant exposed to high Mn. The Mn concentration in the shoots was decreased, but that in the roots was increased by Si in the WT. In contrast, the Mn concentration in the roots and shoots was unaffected by Si in the mutant. Furthermore, Si supply resulted in an increased Mn in the root cell sap, decreased Mn in the xylem sap in the WT, but these effects of Si were not observed in the mutant. A short-term labelling experiment with Mn-54 showed that the uptake of Mn was similar between plants with and without Si and between WT and the mutant. However, Si decreased root-to-shoot translocation of Mn in the WT, but not in the mutant. The expression of a Mn transporter gene for uptake, OsNramp5, was unaffected by a short exposure (< 1 d) to Si, but down-regulated by relatively long-term exposure to Si in WT. In contrast, the expression of OsNramp5 was unaffected by Si in the mutant. These results indicated that Si-decreased Mn accumulation results from both Si-decreased root-to-shoot translocation of Mn, probably by the formation of Mn-Si complex in root cells, and uptake by down-regulating Mn transporter gene.

DOI： 10.1093/jxb/erv545

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：BIOMED CENTRAL LTD  

Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated.
Results: Here, we report results of the functional characterization of the OsHKT1; 4 transporter in rice. OsHKT1; 4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1; 4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4+, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1; 4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, Na-22(+) tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4.
Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.

DOI： 10.1186/s12870-016-0709-4

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Manganese is an essential metal for plant growth. A number of transporters involved in the uptake of manganese from soils, and its translocation to the shoot, have been identified in Arabidopsis and rice. However, the transporter responsible for the radial transport of manganese out of root exodermis and endodermis cells and into the root stele remains unknown. Here, we show that metal tolerance protein 9 (MTP9), a member of the cation diffusion facilitator family, is a critical player in this process in rice (Oryza sativa). We find that MTP9 is mainly expressed in roots, and that the resulting protein is localized to the plasma membrane of exo- and endodermis cells, at the proximal side of these cell layers (opposite the manganese uptake transporter Nramp5, which is found at the distal side). We demonstrate that MTP9 has manganese transport activity by expression in proteoliposomes and yeast, and show that knockout of MTP9 in rice reduces manganese uptake and its translocation to shoots. We conclude that at least in rice MTP9 is required for manganese translocation to the root stele, and thereby manganese uptake.

DOI： 10.1038/NPLANTS.2015.170

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Developing tissues such as meristem with low transpiration require high Zn levels for their active growth, but the molecular mechanisms underlying the preferential distribution to these tissues are poorly understood. We found that a member of the ZIP (ZRT, IRT-like protein), OsZIP3, showed high expression in the nodes of rice (Oryza sativa). Immunostaining revealed that OsZIP3 was localized at the xylem intervening parenchyma cells and xylem transfer cells of the enlarged vascular bundle in both basal and upper nodes. Neither OsZIP3 gene expression nor encoded protein was affected by either deficiency or toxic levels of Zn. Knockdown of OsZIP3 resulted in significantly reduced Zn levels in the shoot basal region containing the shoot meristem and elongating zone, but increased Zn levels in the transpiration flow. A short-term experiment with the Zn-67 stable isotope showed that more Zn was distributed to the lower leaves, but less to the shoot elongating zone and nodes in the knockdown lines compared with the wild-type rice at both the vegetative and reproductive growth stages. Taken together, OsZIP3 located in the node is responsible for unloading Zn from the xylem of enlarged vascular bundles, which is the first step for preferential distribution of Zn to the developing tissues in rice.
Significance Statement Zinc homeostasis is achieved by regulating diverse zinc transporters. Here we show that the zinc transporter OsZIP3 mediates the first step leading to preferential distribution of zinc in developing tissues, by unloading zinc from the xylem of enlarged vascular bundles.

DOI： 10.1111/tpj.13005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Requirement of mineral elements in different plant tissues is not often consistent with their transpiration rate; therefore, plants have developed systems for preferential distribution of mineral elements to the developing tissues with low transpiration. Here we took silicon (Si) as an example and revealed an efficient system for preferential distribution of Si in the node of rice (Oryza sativa). Rice is able to accumulate more than 10% Si of the dry weight in the husk, which is required for protecting the grains from water loss and pathogen infection. However, it has been unknown for a long time how this hyperaccumulation is achieved. We found that three transporters (Lsi2, Lsi3, and Lsi6) located at the node are involved in the intervascular transfer, which is required for the preferential distribution of Si. Lsi2 was polarly localized to the bundle sheath cell layer around the enlarged vascular bundles, which is next to the xylem transfer cell layer where Lsi6 is localized. Lsi3 was located in the parenchyma tissues between enlarged vascular bundles and diffuse vascular bundles. Similar to Lsi6, knockout of Lsi2 and Lsi3 also resulted in decreased distribution of Si to the panicles but increased Si to the flag leaf. Furthermore, we constructed a mathematical model for Si distribution and revealed that in addition to cooperation of three transporters, an apoplastic barrier localized at the bundle sheath cells and development of the enlarged vascular bundles in node are also required for the hyperaccumulation of Si in rice husk.

DOI： 10.1073/pnas.1508987112

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE LONDON  

The high accumulation of silicon (Si) protects plants from biotic and abiotic stresses. Two different types of Si transporter [Low Silicon 1 (Lsi1) and 2 (Lsi2)] involved in the uptake and distribution of Si have been identified. Lsi1, a Si permeable channel, belongs to the Nod26-like major intrinsic protein (NIP) III subgroup of the aquaporin membrane protein family with a distinct selectivity, whereas Lsi2, an efflux Si transporter, belongs to an uncharacterized anion transporter family. These transporters are localized to the plasma membrane, but, in different plant species, show different expression patterns and tissue or cellular localizations that are associated with different levels of Si accumulation. A recent mathematical modeling study revealed that cooperation of Lsi1 and Lsi2, which show a polarized localization, is required for the efficient transport of Si in rice.

DOI： 10.1016/j.tplants.2015.04.007

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Silicon (Si) uptake by the roots is mediated by two different transporters, Lsi1 (passive) and Lsi2 (active), in rice (Oryza sativa). Both transporters are polarly localized in the plasma membranes of exodermal (outer) and endodermal (inner) cells with Casparian strips. However, it is unknown how rice is able to take up large amounts of Si compared with other plants, and why rice Si transporters have a characteristic cellular localization pattern. To answer these questions, we simulated Si uptake by rice roots by developing a mathematical model based on a simple diffusion equation that also accounts for active transport by Lsi2. In this model, we calibrated the model parameters using in vivo experimental data on the Si concentrations in the xylem sap and a Monte Carlo method. In our simulation experiments, we compared the Si uptake between roots with various transporter and Casparian strip locations and estimated the Si transport efficiency of roots with different localization patterns and quantities of the Lsi transporters. We found that the Si uptake by roots that lacked Casparian strips was lower than that of normal roots. This suggests that the doublelayer structure of the Casparian strips is an important factor in the high Si uptake by rice. We also found that among various possible localization patterns, the most efficient one was that of the wild-type rice; this may explain the high Si uptake capacity of rice.

DOI： 10.1093/pcp/pcv017

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Phosphate transporters (PTs) mediate phosphorus uptake and are regulated at the transcriptional and posttranslational levels. In one key mechanism of posttranslational regulation, phosphorylation of PTs affects their trafficking from the endoplasmic reticulum (ER) to the plasma membrane. However, the kinase(s) mediating PT phosphorylation and the mechanism leading to ER retention of phosphorylated PTs remain unclear. In this study, we identified a rice (Oryza sativa) kinase subunit, CK2 beta 3, which interacts with PT2 and PT8 in a yeast two-hybrid screen. Also, the CK2 alpha 3/beta 3 holoenzyme phosphorylates PT8 under phosphate-sufficient conditions. This phosphorylation inhibited the interaction of PT8 with PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1, a key cofactor regulating the exit of PTs from the ER to the plasma membrane. Additionally, phosphorus starvation promoted CK2 beta 3 degradation, relieving the negative regulation of PT phosphorus-insufficient conditions. In accordance, transgenic expression of a nonphosphorylatable version of OsPT8 resulted in elevated levels of that protein at the plasma membrane and enhanced phosphorus accumulation and plant growth under various phosphorus regimes. Taken together, these results indicate that CK2 alpha 3/beta 3 negatively regulates PTs and phosphorus status regulates CK2 alpha 3/beta 3.

DOI： 10.1105/tpc.114.135335

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Ascorbate is an antioxidant and coenzyme for various metabolic reactions in vivo. In plant chloroplasts, high ascorbate levels are required to overcome photoinhibition caused by strong light. However, ascorbate is synthesized in the mitochondria and the molecular mechanisms underlying ascorbate transport into chloroplasts are unknown. Here we show that AtPHT4;4, a member of the phosphate transporter 4 family of Arabidopsis thaliana, functions as an ascorbate transporter. In vitro analysis shows that proteoliposomes containing the purified AtPHT4; 4 protein exhibit membrane potential- and Cl- dependent ascorbate uptake. The AtPHT4; 4 protein is abundantly expressed in the chloroplast envelope membrane. Knockout of AtPHT4; 4 results in decreased levels of the reduced form of ascorbate in the leaves and the heat dissipation process of excessive energy during photosynthesis is compromised. Taken together, these observations indicate that the AtPHT4; 4 protein is an ascorbate transporter at the chloroplast envelope membrane, which may be required for tolerance to strong light stress.

DOI： 10.1038/ncomms6928

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Buckwheat (Fagopyrum esculentum Moench) is a species with high aluminum (Al) tolerance and accumulation. Although the physiological mechanisms for external and internal detoxification of Al have been well studied, the molecular mechanisms responsible are poorly understood. Here, we conducted a genome-wide transcriptome analysis of Al-responsive genes in the roots and leaves using RNA sequencing (RNA-Seq) technology. RNA-Seq generated reads ranging from 56 x 10(6) to 93 x 10(6). A total of 148,734 transcript contigs with an average length of 1,014 bp were assembled, generating 84,516 unigenes. Among them, 31,730 and 23,853 unigenes were annotated, respectively, in the NCBI plant database and TAIR database for Arabidopsis. Of the annotated genes, 4,067 genes in the roots and 2,663 genes in the leaves were up-regulated (>2-fold) by Al exposure, while 2,456 genes in the roots and 2,426 genes in the leaves were down-regulated (<2-fold) A few STOP1/ART1 (SENSITIVE TO PROTON RHIZOTOXICITY1/AL RESISTANCE TRANSCRIPTION FACTOR1)-regulated gene homologs including FeSTAR1, FeALS3 (ALUMINUM SENSITIVE3), FeALS1 (ALUMINUM SENSITIVE1), FeMATE1 and FeMATE2 (MULTIDRUG AND TOXIC COMPOUND EXTRUSION1 and 2) were also up-regulated in buckwheat, indicating some common Al tolerance mechanism across the species, although most STOP1/ART1-regulated gene homologs were not changed. Most genes involved in citric and oxalic acid biosynthesis were not significantly altered. Some transporter genes were highly expressed in the roots and leaves and responded to Al stress, implicating their role in Al tolerance and accumulation. Overall, our data provide a platform for further characterizing the functions of genes involved in Al tolerance and accumulation in buckwheat.

DOI： 10.1093/pcp/pcu135

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Arsenic (As) is a chronic poison that causes severe skin lesions and cancer. Rice (Oryza sativa L.) is a major dietary source of As; therefore, reducing As accumulation in the rice grain and thereby diminishing the amount of As that enters the food chain is of critical importance. Here, we report that a member of the Oryza sativa C-type ATP-binding cassette (ABC) transporter (OsABCC) family, OsABCC1, is involved in the detoxification and reduction of As in rice grains. We found that OsABCC1 was expressed in many organs, including the roots, leaves, nodes, peduncle, and rachis. Expression was not affected when plants were exposed to low levels of As but was up-regulated in response to high levels of As. In both the basal nodes and upper nodes, which are connected to the panicle, OsABCC1 was localized to the phloem region of vascular bundles. Furthermore, OsABCC1 was localized to the tonoplast and conferred phytochelatin-dependent As resistance in yeast. Knockout of OsABCC1 in rice resulted in decreased tolerance to As, but did not affect cadmium toxicity. At the reproductive growth stage, the As content was higher in the nodes and in other tissues of wild-type rice than in those of OsABCC1 knockout mutants, but was significantly lower in the grain. Taken together, our results indicate that OsABCC1 limits As transport to the grains by sequestering As in the vacuoles of the phloem companion cells of the nodes in rice.

DOI： 10.1073/pnas.1414968111

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

As a member of the heavy metal ATPase (HMA) family, OsHMA3 is a tonoplast-localized transporter for Cd in the roots of rice (Oryza sativa). Overexpression of OsHMA3 selectively reduces Cd accumulation in the grain. Further characterization in the present study revealed that overexpression of OsHMA3 also enhances the tolerance to toxic Cd. The growth of both the roots and shoots was similar in the absence of Cd between an OsHMA3-overexpressed line and vector control, but the Cd-inhibited growth was significantly alleviated in the OsHMA3-overexpressed line. The over-expressed line showed higher Cd concentration in the roots, but lower Cd concentration in the shoots compared with the wild-type rice and vector control line, indicating that overexpression of OsHMA3 enhanced vacuolar sequestration of Cd in the roots. The Zn concentration in the roots of the OsHMA3-overexpressed line was constantly higher than that of vector control, but the Zn concentration in the shoots was similar between the overexpressed line and vector control. Five transporter genes belonging to the ZIP family were constitutively up-regulated in the OsHMA3-overexpressed line. These results suggest that shoot Zn level was maintained by up-regulating these genes involved in the Zn uptake/translocation. Taken together, overexpression of OsHMA3 is an efficient way to reduce Cd accumulation in the grain and to enhance Cd tolerance in rice.

DOI： 10.1093/jxb/eru340

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE LONDON  

Mineral elements, including both essential and toxic elements, are delivered to different tissues after they are taken up from the roots, but the mechanism (or mechanisms) underlying the distribution remains poorly understood. In graminaceous plants, this distribution occurs in nodes, which have a complex, well-organized vascular system. A transfer of mineral elements between different vascular bundles is required, especially for preferential distribution to developing tissues that have low transpiration but high nutrient requirements. This intervascular transfer is mediated by various transporters localized at different cells in the node. In this opinion article, we propose four modes of distribution for different mineral elements: xylem-switch, phloem-tropic, phloem-kickback, and minimum-shift, based on specific molecular transport processes identified in the nodes mainly of rice (Oryza sativa). We also discuss the prospects for future studies on mineral nutrient distribution in the nodes.

DOI： 10.1016/j.tplants.2014.05.007

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

Mid-bicellular pollen vegetative cells in tobacco escape from G1 arrest and proceed to the G1/S transition towards androgenesis within 1 day under glutamine starvation conditions in vitro.
In the Nicotiana tabacum pollen culture system, immature pollen grains at the mid-bicellular stage can mature in the presence of glutamine; however, if glutamine is absent, they deviate from their native cell fate in a few days. The glutamine-starved pollen grains cannot undergo maturation, even when supplied with glutamine later. Instead, they undergo cell division towards androgenesis slowly within 10 days in a medium containing appropriate nutrients. During the culture period, they ought to escape from G1 arrest to proceed into S phase as the primary step towards androgenesis. However, this event has not been experimentally confirmed. Here, we demonstrated that the pollen vegetative cells proceeded to the G1/S transition within approximately 15-36 h after the start of culture. These results were obtained by analyzing transgenic pollen possessing a fusion gene encoding nuclear-localizing GFP under the control of an E2F motif-containing promoter isolated from a gene encoding one of DNA replication licensing factors. Observations using a 5-ethynyl-2'-deoxyuridine DNA labeling and detection technique uncovered that the G1/S transition was soon followed by S phase. These hallmarks of vegetative cells undergoing dedifferentiation give us new insights into upstream events causing the G1/S transition and also provide a novel strategy to increase the frequency of the androgenic response in tobacco and other species, including recalcitrants.

DOI： 10.1007/s00299-014-1640-5

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Although rice (Oryza sativa) is the most Al-tolerant species among small-grain cereal crops, there is wide genotypic variation in its tolerance to Al toxicity. A number of quantitative trait loci (QTLs) for Al tolerance have been detected, but the responsible genes have not been identified. By using chromosome segment substitution lines, this work found that Nrat1, a gene encoding an Al transporter, is responsible for a QTL previously detected on chromosome 2. Substitution of the chromosome segment containing Nrat1 from Koshihikari (Al-tolerant variety) by that from Kasalath (Al-sensitive variety) decreased Nrat1 expression and Al uptake and tolerance, but increased binding of Al to the cell wall. Nrat1 in Kasalath showed tissue localization similar to Koshihikari in the roots. Although Koshihikari and Kasalath differed in four amino acids in Nrat1 protein, Nrat1 from Kasalath also showed transport activity for Al. Analysis with site-directed mutagenesis revealed that these differences did not affect the Al-transport activity much. Furthermore, there was no correlation between Al tolerance and the open-reading-frame sequence differences in other rice varieties. On the other hand, there was good correlation between Nrat1 expression and Al tolerance; however, sequence comparison of the promoter region up to 2.1 kb did not give a clear difference between the Al-tolerant and -sensitive varieties. Taken together, these results indicate that differential expression of Nrat1 is responsible for the QTL for Al tolerance on chromosome 2, although the mechanism controlling Nrat1 expression remains to be examined.

DOI： 10.1093/jxb/eru201

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Cultivated rice (Oryza sativa) accumulates high concentration of silicon (Si), which is required for its high and sustainable production. High Si accumulation in cultivated rice is achieved by a high expression of both influx (Lsi1) and efflux (Lsi2) Si transporters in roots. Herein, we physiologically investigated Si uptake, isolated and functionally characterized Si transporters in six wild rice species with different genome types. Si uptake by the roots was lower in Oryza rufipogon, Oryza barthii (AA genome), Oryza australiensis (EE genome) and Oryza punctata (BB genome), but similar in Oryza glumaepatula and Oryza meridionalis (AA genome) compared with the cultivated rice (cv. Nipponbare). However, all wild rice species and the cultivated rice showed similar concentration of Si in the shoots when grown in a field. All species with AA genome showed the same amino acid sequence of both Lsi1 and Lsi2 as O. sativa, whereas species with EE and BB genome showed several nucleotide differences in both Lsi1 and Lsi2. However, proteins encoded by these genes also showed transport activity for Si in Xenopus oocyte. The mRNA expression of Lsi1 in all wild rice species was lower than that in the cultivated rice, whereas the expression of Lsi2 was lower in O. rufipogon and O. barthii but similar in other species. Similar cellular localization of Lsi1 and Lsi2 was observed in all wild rice as the cultivated rice. These results indicate that superior Si uptake, the important trait for rice growth, is basically conserved in wild and cultivated rice species.

DOI： 10.1111/ppl.12125

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

The Zn/Cd hyperaccumulator, Noccaea caerulescens, has been studied extensively for its ability to accumulate high levels of Zn and Cd in its leaves. Previous studies have indicated that the Zn and Cd hyperaccumulation trait exhibited by this species involves different transport and tolerance mechanisms. It has also been well documented that certain ecotypes of N.caerulescens are much better Cd hyperaccumulators than others. However, there does not seem to be much ecotypic variation for Zn hyperaccumulation in N.caerulescens. In this study we employed a comparative transcriptomics approach to look at root and shoot gene expression in Ganges and Prayon plants in response to Cd stress to identify transporter genes that were more highly expressed in either the roots or shoots of the superior Cd accumulator, Ganges. Comparison of the transcriptomes from the two ecotypes of Noccaea caerulescens identified a number of genes that encoded metal transporters that were more highly expressed in the Ganges ecotype in response to Cd stress. Characterization of one of these transporters, NcNramp1, showed that it is involved in the influx of Cd across the endodermal plasma membrane and thus may play a key role in Cd flux into the stele and root-to-shoot Cd transport. NcNramp1 may be one of the main transporters involved in Cd hyperaccumulation in N.caerulescens and copy number variation appears to be the main reason for high NcNramp1 gene expression underlying the increased Cd accumulation in the Ganges ecotype.

DOI： 10.1111/tpj.12480

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Plant roots play an important role in the uptake of water and nutrients, structural support and environmental sensing, but the molecular mechanisms involved in root development are poorly understood in rice (Oryza sativa), which is characterized by a dense fibrous root system. Here we report a rice mutant (red1 for root elongation defect 1) with short roots. Morphological and physiological analyses showed that the mutant had a shorter length from the quiescent center (QC) to the starting point of the elongation zone but a similar cell size and number of lateral and crown roots compared with the wild type. Furthermore, the mutant had similar radial structure and nutrient uptake patterns to the wild type. Map-based cloning revealed that the mutant phenotype was caused by a point mutation of a gene encoding an argininosuccinate lyase (ASL), catalyzing the last step of arginine biosynthesis. The OsASL1 gene has two distinct transcripts, OsASL1.1 and OsASL1.2, which result from different transcription start sites, but only OsASL1.1 was able to complement the mutant phenotype. OsASL1.1 was expressed in both the roots and shoots. The protein encoded by OsASL1.1 showed ASL activity in yeast. OsALS1.1 was localized to the plastid. The short root of the mutant was rescued by exogenous addition of arginine, but not by other amino acids. These results indicate that arginine produced by ASL is required for normal root elongation in rice.

DOI： 10.1111/tpj.12476

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Landes Bioscience  

Plant roots play an important role in uptake of water and nutrients, support of above-ground part and environmental sensing, but the molecular mechanisms underlying the root development are poorly understood in rice. We found that a gene (OsASL1) encoding argininosuccinate lyase is involved in normal root development of rice. OsASL1 cleaves argininosuccinate to arginine and fumarate reversibly, the last step in the arginine biosynthetic pathway. Here, we further characterized OsASL1 in terms of expression pattern, subcellular localization, and arginine effect on the root growth. A detailed expression analysis revealed that 2 transcripts of OsASL1, OsASL1.1 and OsASL1.2, showed different expression patterns
OsASL1.1 was expressed in most organs throughout the whole growth period, whereas OsASL1.2 was mainly expressed in the roots. In contrast to plastid-localized OsASL1.1, OsASL1.2 was localized to the cytosol and nucleus. The short-root phenotype of the mutant was not rescued by exogenous addition of the sodium nitroprusside, a nitric oxide donor, but rescued by an appropriate concentration of Arg. Our results indicate that the subcellular localization was determined by the N terminus of OsASL1 and that appropriate concentration of Arg is required for normal root elongation in rice. © 2014 Landes Bioscience.

DOI： 10.4161/psb.28717

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Heavy metal-transporting P-type ATPase (HMA) has been implicated in the transport of heavy metals in plants. Here, we report the function and role of an uncharacterized member of HMA, OsHMA5 in rice (Oryza sativa). Knockout of OsHMA5 resulted in a decreased copper (Cu) concentration in the shoots but an increased Cu concentration in the roots at the vegetative stage. At the reproductive stage, the concentration of Cu in the brown rice was significantly lower in the mutants than in the wild-type rice; however, there was no difference in the concentrations of iron, manganese, and zinc between two independent mutants and the wild type. The Cu concentration of xylem sap was lower in the mutants than in the wild-type rice. OsHMA5 was mainly expressed in the roots at the vegetative stage but also in nodes, peduncle, rachis, and husk at the reproductive stage. The expression was up-regulated by excess Cu but not by the deficiency of Cu and other metals, including zinc, iron, and manganese, at the vegetative stage. Analysis of the transgenic rice carrying the OsHMA5 promoter fused with green fluorescent protein revealed that it was localized at the root pericycle cells and xylem region of diffuse vascular bundles in node I, vascular tissues of peduncle, rachis, and husk. Furthermore, immunostaining with an antibody against OsHMA5 revealed that it was localized to the plasma membrane. Expression of OsHMA5 in a Cu transport-defective mutant yeast (Saccharomyces cerevisiae) strain restored the growth. Taken together, OsHMA5 is involved in loading Cu to the xylem of the roots and other organs.

DOI： 10.1104/pp.113.226225

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掲載種別：研究論文（学術雑誌）  

Manganese (Mn) is an essential micronutrient for plants, but is toxic when present in excess. The rice plant (Oryza sativa L.) accumulates high concentrations of Mn in the aerial parts; however, the molecular basis for Mn tolerance is poorly understood. In the present study, genes encoding Mn tolerance were screened for by expressing cDNAs of genes from rice shoots in Saccharomyces cerevisiae. A gene encoding a cation diffusion facilitator (CDF) family member, OsMTP8.1, was isolated, and its expression was found to enhance Mn accumulation and tolerance in S. cer-evisiae. In plants, OsMTP8.1 and its transcript were mainly detected in shoots. High or low supply of Mn moderately induced an increase or decrease in the accumulation of OsMTP8.1, respectively. OsMTP8.1 was detected in all cells of leaf blades through immunohistochemistry. OsMTP8.1 fused to green fluorescent protein was localized to the tonoplast. Disruption of OsMTP8.1 resulted in decreased chlorophyll levels, growth inhibition in the presence of high concentrations of Mn, and decreased accumulation of Mn in shoots and roots. However, there was no difference in the accumulation of other metals, including Zn, Cu, Fe, Mg, Ca, and K. These results suggest that OsMTP8.1 is an Mn-specific transporter that sequesters Mn into vacuoles in rice and is required for Mn tolerance in shoots. © The Author 2013.

DOI： 10.1093/jxb/ert243

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

A transcription factor for Al tolerance, ART1, regulates the expression of at least 30 genes in rice. Here we functionally characterized one of the downstream genes, OsCDT3, which encodes a predicted peptide of only 53 amino acid residues rich in cysteine. Knockdown of this gene resulted in decreased tolerance to Al, but did not affect the tolerance to Cd. The aluminum (Al) content in the root residues including cell wall and the plasma membrane of knockdown lines decreased, but the Al concentration in the root cell sap increased compared with those of the wild-type rice. OsCDT3 was mainly expressed in the roots and its expression was specifically induced by Al exposure, not by low pH and other metals. There was a small genotypic variation in OsCDT3 expression level, but no correlation between Al tolerance and the OsCDT3 variation was found among 17 rice cultivars. Analysis of pOsCDT3::GFP transgenic rice showed that OsCDT3 was expressed at all cells in the root tips. Transient expression of OsCDT3 fused with GFP at both N- and C-termini showed that OsCDT3 was anchored to the plasma membrane. Expression of OsCDT3 in yeast conferred tolerance to Al, but not to Cd. Furthermore, OsCDT3 did not show transport activity for Al in yeast, but was able to directly bind Al in vitro. Taken together, our results indicate that OsCDT3 anchoring to the plasma membrane may play a role in stopping entry of Al into the root cells by binding Al, therefore, contributing to high Al tolerance in rice.

DOI： 10.1111/tpj.12296

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Yorkshire fog (Holcus lanatus), which belongs to the Poaceae family and is a close relative of the agronomic crop oat (Avena sativa), is a widely adaptable grass species that is able to grow on highly acidic soils with high levels of Al, but the mechanism underlying the high Al tolerance is unknown. Here, we characterized two accessions of H.lanatus collected from an acid plot (soil pH 3.6, HL-A) and a neutral plot (pH 7.1, HL-N) in terms of Al tolerance, organic acid anion secretion and related gene expression. In response to Al (pH 4.5), the HL-A roots secreted approximately twice as much malate as the HL-N roots, but there was no difference in citrate secretion. Cloning of the gene HlALMT1 responsible for malate secretion showed that the encoded amino acid sequence did not differ between two accessions, but the expression level in the outer cell layers of the HL-A roots was twice as high as in the HL-N roots. This difference was not due to the genomic copy number, but was due to the number of cis-acting elements for an Al-responsive transcription factor (HlART1) in the promoter region of HlALMT1, as demonstrated by both a yeast one-hybrid assay and a transient assay in tobacco protoplasts. Furthermore, introduction of HlALMT1 driven by the HL-A promoter into rice resulted in significantly more Al-induced malate secretion than introduction of HlALMT1 driven by the HL-N promoter. These findings indicate that the adaptation of H.lanatus to acidic soils may be achieved by increasing number of cis-acting elements for ART1 in the promoter region of the HlALMT1 gene, enhancing the expression of HlALMT1 and the secretion of malate.

DOI： 10.1111/tpj.12266

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Mineral nutrients, such as manganese, are required for the development of plants and their reproductive organs, but these can be toxic if accumulated at high concentrations. Therefore, plants must have a system for preferentially delivering an adequate amount of minerals to these organs for active growth and development, while preventing mineral overaccumulation in the face of changing environments. Here we show that a member of the Nramp transporter family, OsNramp3, functions as a switch in response to environmental Mn changes. OsNramp3 is constitutively expressed in the node, a junction of vasculatures connecting leaves, stems and panicles. At low Mn concentration, OsNramp3 preferentially transports Mn to young leaves and panicles. However, at high Mn concentration, the OsNramp3 protein is rapidly degraded within a few hours, resulting in the distribution of Mn to old tissues. Our results reveal the OsNramp3-mediated strategy of rice for adapting to a wide change of Mn in the environment.

DOI： 10.1038/ncomms3442

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Developing tissues such as meristems and reproductive organs require high zinc, but the molecular mechanisms of how zinc taken up by the roots is preferentially delivered to these tissues with low transpiration are unknown. Here, we report that rice (Oryza sativa) heavy metal ATPase2 (OsHMA2), a member of P-type ATPases, is involved in preferential delivery of zinc to the developing tissues in rice. OsHMA2 was mainly expressed in the mature zone of the roots at the vegetative stage, but higher expression was also found in the nodes at the reproductive stage. The expression was unaffected by either zinc deficiency or zinc excess. OsHMA2 was localized at the pericycle of the roots and at the phloem of enlarged and diffuse vascular bundles in the nodes. Heterologous expression of OsHMA2 in yeast (Saccharomyces cerevisiae) showed influx transport activity for zinc as well as cadmium. Two independent Tos17 insertion lines showed decreased zinc concentration in the crown root tips, decreased concentration of zinc and cadmium in the upper nodes and reproductive organs compared with wild-type rice. Furthermore, a short-term labeling experiment with Zn-67 showed that the distribution of zinc to the panicle and uppermost node I was decreased, but that, to the lower nodes, was increased in the two mutants. Taken together, OsHMA2 in the nodes plays an important role in preferential distribution of zinc as well as cadmium through the phloem to the developing tissues.

DOI： 10.1104/pp.113.216564

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Barley (Hordeum vulgare) spikes are developmentally switched from two-rowed to six-rowed by a single recessive gene, six-rowed spike 1 (vrs1), which encodes a homeodomain-leucine zipper I class transcription factor. Vrs1 is a paralog of HvHox2 and both were generated by duplication of an ancestral gene. HvHox2 is conserved among cereals, whereas Vrs1 acquired its current function during the evolution of barley. It was unclear whether divergence of expression pattern or protein function accounted for the functionalization of Vrs1. Here, we conducted a comparative analysis of protein functions and gene expression between HvHox2 and Vrs1 to clarify the functionalization mechanism. We revealed that the transcriptional activation activity of HvHOX2 and VRS1 was conserved. In situ hybridization analysis showed that HvHox2 is localized in vascular bundles in developing spikes, whereas Vrs1 is expressed exclusively in the pistil, lemma, palea and lodicule of lateral spikelets. The transcript abundance of Vrs1 was > 10-fold greater than that of HvHox2 during the pistil developmental stage, suggesting that the essential function of Vrs1 is to inhibit gynoecial development. We demonstrated the quantitative function of Vrs1 using RNAi transgenic plants and Vrs1 expression variants. Expression analysis of six-rowed spike mutants that are nonallelic to vrs1 showed that Vrs1 expression was up-regulated by Vrs4, whereas HvHox2 expression was not. These data demonstrate that the divergence of gene expression pattern contributed to the neofunctionalization of Vrs1.

DOI： 10.1111/nph.12068

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Barley (Hordeum vulgare) spikes are developmentally switched from two-rowed to six-rowed by a single recessive gene, six-rowed spike 1 (vrs1), which encodes a homeodomain-leucine zipper I class transcription factor. Vrs1 is a paralog of HvHox2 and both were generated by duplication of an ancestral gene. HvHox2 is conserved among cereals, whereas Vrs1 acquired its current function during the evolution of barley. It was unclear whether divergence of expression pattern or protein function accounted for the functionalization of Vrs1. Here, we conducted a comparative analysis of protein functions and gene expression between HvHox2 and Vrs1 to clarify the functionalization mechanism. We revealed that the transcriptional activation activity of HvHOX2 and VRS1 was conserved. In situ hybridization analysis showed that HvHox2 is localized in vascular bundles in developing spikes, whereas Vrs1 is expressed exclusively in the pistil, lemma, palea and lodicule of lateral spikelets. The transcript abundance of Vrs1 was > 10-fold greater than that of HvHox2 during the pistil developmental stage, suggesting that the essential function of Vrs1 is to inhibit gynoecial development. We demonstrated the quantitative function of Vrs1 using RNAi transgenic plants and Vrs1 expression variants. Expression analysis of six-rowed spike mutants that are nonallelic to vrs1 showed that Vrs1 expression was up-regulated by Vrs4, whereas HvHox2 expression was not. These data demonstrate that the divergence of gene expression pattern contributed to the neofunctionalization of Vrs1.

DOI： 10.1111/nph.12068

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PUBLIC LIBRARY SCIENCE  

Due to the ease with which chromosomes can be observed, the Allium species, and onion in particular, have been familiar materials employed in cytogenetic experiments in biology. In this study, centromeric histone H3 (CENH3)-coding cDNAs were identified in four Allium species (onion, welsh onion, garlic and garlic chives) and cloned. Anti-CENH3 antibody was then raised against a deduced amino acid sequence of CENH3 of welsh onion. The antibody recognized all CENH3 orthologs of the Allium species tested. Immunostaining with the antibody enabled clear visualization of chromosome behavior during mitosis in the species. Furthermore, three-dimensional (3D) observation of mitotic cell division was achieved by subjecting root sections to immunohistochemical techniques. The 3D dynamics of the cells and position of cell-cycle marker proteins (CENH3 and alpha-tubulin) were clearly revealed by immunohistochemical staining with the antibodies. The immunohistochemical analysis made it possible to establish an overview of the location of dividing cells in the root tissues. This breakthrough in technique, in addition to the two centromeric DNA sequences isolated from welsh onion by chromatin immuno-precipitation using the antibody, should lead to a better understanding of plant cell division. A phylogenetic analysis of Allium CENH3s together with the previously reported plant CENH3s showed two separate clades for monocot species tested. One clade was made from CENH3s of the Allium species with those of Poaceae species, and the other from CENH3s of a holocentric species (Luzula nivea). These data may imply functional differences of CENH3s between holocentric and monocentric species. Centromeric localization of DNA sequences isolated from welsh onion by chromatin immunoprecipitation (ChIP) using the antibody was confirmed by fluorescence in situ hybridization and ChIP-quantitative PCR.

DOI： 10.1371/journal.pone.0051315

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PUBLIC LIBRARY SCIENCE  

Due to the ease with which chromosomes can be observed, the Allium species, and onion in particular, have been familiar materials employed in cytogenetic experiments in biology. In this study, centromeric histone H3 (CENH3)-coding cDNAs were identified in four Allium species (onion, welsh onion, garlic and garlic chives) and cloned. Anti-CENH3 antibody was then raised against a deduced amino acid sequence of CENH3 of welsh onion. The antibody recognized all CENH3 orthologs of the Allium species tested. Immunostaining with the antibody enabled clear visualization of chromosome behavior during mitosis in the species. Furthermore, three-dimensional (3D) observation of mitotic cell division was achieved by subjecting root sections to immunohistochemical techniques. The 3D dynamics of the cells and position of cell-cycle marker proteins (CENH3 and alpha-tubulin) were clearly revealed by immunohistochemical staining with the antibodies. The immunohistochemical analysis made it possible to establish an overview of the location of dividing cells in the root tissues. This breakthrough in technique, in addition to the two centromeric DNA sequences isolated from welsh onion by chromatin immuno-precipitation using the antibody, should lead to a better understanding of plant cell division. A phylogenetic analysis of Allium CENH3s together with the previously reported plant CENH3s showed two separate clades for monocot species tested. One clade was made from CENH3s of the Allium species with those of Poaceae species, and the other from CENH3s of a holocentric species (Luzula nivea). These data may imply functional differences of CENH3s between holocentric and monocentric species. Centromeric localization of DNA sequences isolated from welsh onion by chromatin immunoprecipitation (ChIP) using the antibody was confirmed by fluorescence in situ hybridization and ChIP-quantitative PCR.

DOI： 10.1371/journal.pone.0051315

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Silicon (Si) is a beneficial element for plant growth. In barley (Hordeum vulgare), Si uptake by the roots is mainly mediated by a Si channel, Low Silicon1 (HvLsi1), and an efflux transporter, HvLsi2. However, transporters involved in the distribution of Si in the shoots have not been identified. Here, we report the functional characterization of a homolog of HvLsi1, HvLsi6. HvLsi6 showed permeability for Si and localized to the plasma membrane. At the vegetative growth stage, HvLsi6 was expressed in both the roots and shoots. The expression level was unaffected by Si supply. In the roots, HvLsi6 was localized in epidermis and cortex cells of the tips, while in the leaf blades and sheaths, HvLsi6 was only localized at parenchyma cells of vascular bundles. At the reproductive growth stage, high expression of HvLsi6 was also found in the nodes. HvLsi6 in node I was polarly located at the transfer cells surrounding the enlarged vascular bundles toward the numerous xylem vessels. These results suggest that HvLsi6 is involved in Si uptake in the root tips, xylem unloading of Si in leaf blade and sheath, and intervascular transfer of Si in the nodes. Furthermore, HvLsi2 was found to be localized at the parenchyma cell layer adjacent to the transfer cells with opposite polarity of HvLsi6, suggesting that the coupling of HvLsi6 and HvLsi2 is involved in the intervascular transfer of Si at the nodes. Si translocated via the enlarged vascular bundles is unloaded to the transfer cells by HvLsi6, followed by HvLsi2 to reload Si to the diffuse vascular bundles, which are connected to the upper part of the plant, especially the panicles, the ultimate Si sink.

DOI： 10.1104/pp.112.204578

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Silicon (Si) is a beneficial element for plant growth. In barley (Hordeum vulgare), Si uptake by the roots is mainly mediated by a Si channel, Low Silicon1 (HvLsi1), and an efflux transporter, HvLsi2. However, transporters involved in the distribution of Si in the shoots have not been identified. Here, we report the functional characterization of a homolog of HvLsi1, HvLsi6. HvLsi6 showed permeability for Si and localized to the plasma membrane. At the vegetative growth stage, HvLsi6 was expressed in both the roots and shoots. The expression level was unaffected by Si supply. In the roots, HvLsi6 was localized in epidermis and cortex cells of the tips, while in the leaf blades and sheaths, HvLsi6 was only localized at parenchyma cells of vascular bundles. At the reproductive growth stage, high expression of HvLsi6 was also found in the nodes. HvLsi6 in node I was polarly located at the transfer cells surrounding the enlarged vascular bundles toward the numerous xylem vessels. These results suggest that HvLsi6 is involved in Si uptake in the root tips, xylem unloading of Si in leaf blade and sheath, and intervascular transfer of Si in the nodes. Furthermore, HvLsi2 was found to be localized at the parenchyma cell layer adjacent to the transfer cells with opposite polarity of HvLsi6, suggesting that the coupling of HvLsi6 and HvLsi2 is involved in the intervascular transfer of Si at the nodes. Si translocated via the enlarged vascular bundles is unloaded to the transfer cells by HvLsi6, followed by HvLsi2 to reload Si to the diffuse vascular bundles, which are connected to the upper part of the plant, especially the panicles, the ultimate Si sink.

DOI： 10.1104/pp.112.204578

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PUBLIC LIBRARY SCIENCE  

Rice (Oryza sativa) is the most aluminum (Al)-tolerant crop among small-grain cereals, but the mechanism underlying its high Al resistance is still not well understood. To understand the mechanisms underlying high Al-tolerance, we performed a comparative genome-wide transcriptional analysis by comparing expression profiling between the Al-tolerance cultivar (Koshihikari) and an Al-sensitive mutant star1 (SENSITIVE TO AL RHIZOTOXICITY 1) in both the root tips and the basal roots. Exposure to 20 mu M AlCl3 for 6 h resulted in up-regulation (higher than 3-fold) of 213 and 2015 genes including 185 common genes in the root tips of wild-type and the mutant, respectively. On the other hand, in the basal root, genes up-regulated by Al were 126 and 2419 including 76 common genes in the wild-type and the mutant, respectively. These results indicate that Al-response genes are not only restricted to the root tips, but also in the basal root region. Analysis with genes up-or down-regulated only in the wild-type reveals that there are other mechanisms for Al-tolerance except for a known transcription factor ART1-regulated one in rice. These mechanisms are related to nitrogen assimilation, secondary metabolite synthesis, cell-wall synthesis and ethylene synthesis. Although the exact roles of these putative tolerance genes remain to be examined, our data provide a platform for further work on Al-tolerance in rice.

DOI： 10.1371/journal.pone.0048197

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PUBLIC LIBRARY SCIENCE  

Rice (Oryza sativa) is the most aluminum (Al)-tolerant crop among small-grain cereals, but the mechanism underlying its high Al resistance is still not well understood. To understand the mechanisms underlying high Al-tolerance, we performed a comparative genome-wide transcriptional analysis by comparing expression profiling between the Al-tolerance cultivar (Koshihikari) and an Al-sensitive mutant star1 (SENSITIVE TO AL RHIZOTOXICITY 1) in both the root tips and the basal roots. Exposure to 20 mu M AlCl3 for 6 h resulted in up-regulation (higher than 3-fold) of 213 and 2015 genes including 185 common genes in the root tips of wild-type and the mutant, respectively. On the other hand, in the basal root, genes up-regulated by Al were 126 and 2419 including 76 common genes in the wild-type and the mutant, respectively. These results indicate that Al-response genes are not only restricted to the root tips, but also in the basal root region. Analysis with genes up-or down-regulated only in the wild-type reveals that there are other mechanisms for Al-tolerance except for a known transcription factor ART1-regulated one in rice. These mechanisms are related to nitrogen assimilation, secondary metabolite synthesis, cell-wall synthesis and ethylene synthesis. Although the exact roles of these putative tolerance genes remain to be examined, our data provide a platform for further work on Al-tolerance in rice.

DOI： 10.1371/journal.pone.0048197

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PUBLIC LIBRARY SCIENCE  

Rice (Oryza sativa) is the most aluminum (Al)-tolerant crop among small-grain cereals, but the mechanism underlying its high Al resistance is still not well understood. To understand the mechanisms underlying high Al-tolerance, we performed a comparative genome-wide transcriptional analysis by comparing expression profiling between the Al-tolerance cultivar (Koshihikari) and an Al-sensitive mutant star1 (SENSITIVE TO AL RHIZOTOXICITY 1) in both the root tips and the basal roots. Exposure to 20 mu M AlCl3 for 6 h resulted in up-regulation (higher than 3-fold) of 213 and 2015 genes including 185 common genes in the root tips of wild-type and the mutant, respectively. On the other hand, in the basal root, genes up-regulated by Al were 126 and 2419 including 76 common genes in the wild-type and the mutant, respectively. These results indicate that Al-response genes are not only restricted to the root tips, but also in the basal root region. Analysis with genes up-or down-regulated only in the wild-type reveals that there are other mechanisms for Al-tolerance except for a known transcription factor ART1-regulated one in rice. These mechanisms are related to nitrogen assimilation, secondary metabolite synthesis, cell-wall synthesis and ethylene synthesis. Although the exact roles of these putative tolerance genes remain to be examined, our data provide a platform for further work on Al-tolerance in rice.

DOI： 10.1371/journal.pone.0048197

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Cu is an essential element for plant growth, but the molecular mechanisms of its distribution and redistribution within the plants are unknown. Here, we report that Yellow stripe-like16 (YSL16) is involved in Cu distribution and redistribution in rice (Oryza sativa). Rice YSL16 was expressed in the roots, leaves, and unelongated nodes at the vegetative growth stage and highly expressed in the upper nodes at the reproductive stage. YSL16 was expressed at the phloem of nodes and vascular tissues of leaves. Knockout of this gene resulted in a higher Cu concentration in the older leaves but a lower concentration in the younger leaves at the vegetative stage. At the reproductive stage, a higher Cu concentration was found in the flag leaf and husk, but less Cu was present in the brown rice, resulting in a significant reduction in fertility in the knockout line. Isotope labeling experiments with Cu-65 showed that the mutant lost the ability to transport Cu-nicotianamine from older to younger leaves and from the flag leaf to the panicle. Rice YSL16 transported the Cu-nicotianamine complex in yeast. Taken together, our results indicate that Os-YSL16 is a Cu-nicotianamine transporter that is required for delivering Cu to the developing young tissues and seeds through phloem transport.

DOI： 10.1105/tpc.112.103820

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Cu is an essential element for plant growth, but the molecular mechanisms of its distribution and redistribution within the plants are unknown. Here, we report that Yellow stripe-like16 (YSL16) is involved in Cu distribution and redistribution in rice (Oryza sativa). Rice YSL16 was expressed in the roots, leaves, and unelongated nodes at the vegetative growth stage and highly expressed in the upper nodes at the reproductive stage. YSL16 was expressed at the phloem of nodes and vascular tissues of leaves. Knockout of this gene resulted in a higher Cu concentration in the older leaves but a lower concentration in the younger leaves at the vegetative stage. At the reproductive stage, a higher Cu concentration was found in the flag leaf and husk, but less Cu was present in the brown rice, resulting in a significant reduction in fertility in the knockout line. Isotope labeling experiments with Cu-65 showed that the mutant lost the ability to transport Cu-nicotianamine from older to younger leaves and from the flag leaf to the panicle. Rice YSL16 transported the Cu-nicotianamine complex in yeast. Taken together, our results indicate that Os-YSL16 is a Cu-nicotianamine transporter that is required for delivering Cu to the developing young tissues and seeds through phloem transport.

DOI： 10.1105/tpc.112.103820

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Magnesium (Mg)-mediated alleviation of aluminum (Al) toxicity has been observed in a number of plant species, but the mechanisms underlying the alleviation are still poorly understood. When a putative rice (Oryza sativa) Mg transporter gene, Oryza sativa MAGNESIUM TRANSPORTER1 (OsMGT1), was knocked out, the tolerance to Al, but not to cadmium and lanthanum, was decreased. However, this inhibition could be rescued by addition of 10 mu M Mg, but not by the same concentration of barium or strontium. OsMGT1 was expressed in both the roots and shoots in the absence of Al, but the expression only in the roots was rapidly up-regulated by Al. Furthermore, the expression did not respond to low pH and other metals including cadmium and lanthanum, and was regulated by an Al-responsive transcription factor, AL RESISTANCE TRANSCRIPTION FACTOR1. An investigation of subcellular localization showed that OsMGT1 was localized to the plasma membrane. A short-term (30 min) uptake experiment with stable isotope Mg-25 showed that knockout of OsMGT1 resulted in decreased Mg uptake, but that the uptake in the wild type was enhanced by Al. Mg concentration in the cell sap of the root tips was also increased in the wild-type rice, but not in the knockout lines in the presence of Al. A microarray analysis showed that transcripts of genes related to stress were more up- and down-regulated in the knockout lines. Taken together, our results indicate that OsMGT1 is a transporter for Mg uptake in the roots and that up-regulation of this gene is required for conferring Al tolerance in rice by increasing Mg concentration in the cell.

DOI： 10.1104/pp.112.199778

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Magnesium (Mg)-mediated alleviation of aluminum (Al) toxicity has been observed in a number of plant species, but the mechanisms underlying the alleviation are still poorly understood. When a putative rice (Oryza sativa) Mg transporter gene, Oryza sativa MAGNESIUM TRANSPORTER1 (OsMGT1), was knocked out, the tolerance to Al, but not to cadmium and lanthanum, was decreased. However, this inhibition could be rescued by addition of 10 mu M Mg, but not by the same concentration of barium or strontium. OsMGT1 was expressed in both the roots and shoots in the absence of Al, but the expression only in the roots was rapidly up-regulated by Al. Furthermore, the expression did not respond to low pH and other metals including cadmium and lanthanum, and was regulated by an Al-responsive transcription factor, AL RESISTANCE TRANSCRIPTION FACTOR1. An investigation of subcellular localization showed that OsMGT1 was localized to the plasma membrane. A short-term (30 min) uptake experiment with stable isotope Mg-25 showed that knockout of OsMGT1 resulted in decreased Mg uptake, but that the uptake in the wild type was enhanced by Al. Mg concentration in the cell sap of the root tips was also increased in the wild-type rice, but not in the knockout lines in the presence of Al. A microarray analysis showed that transcripts of genes related to stress were more up- and down-regulated in the knockout lines. Taken together, our results indicate that OsMGT1 is a transporter for Mg uptake in the roots and that up-regulation of this gene is required for conferring Al tolerance in rice by increasing Mg concentration in the cell.

DOI： 10.1104/pp.112.199778

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

In this paper, we conducted a detailed analysis of the ZIP family transporter, NcZNT1, in the zinc (Zn)/cadmium (Cd) hyperaccumulating plant species, Noccaea caerulescens, formerly known as Thlaspi caerulescens. NcZNT1 was previously suggested to be the primary root Zn/Cd uptake transporter. Both a characterization of NcZNT1 transport function in planta and in heterologous systems, and an analysis of NcZNT1 gene expression and NcZNT1 protein localization were carried out. We show that NcZNT1 is not only expressed in the root epidermis, but also is highly expressed in the root and shoot vasculature, suggesting a role in long-distance metal transport. Also, NcZNT1 was found to be a plasma membrane transporter that mediates Zn but not Cd, iron (Fe), manganese (Mn) or copper (Cu) uptake into plant cells. Two novel regions of the NcZNT1 promoter were identified which may be involved in both the hyperexpression of NcZNT1 and its ability to be regulated by plant Zn status. In conclusion, we demonstrate here that NcZNT1 plays a role in Zn and not Cd uptake from the soil, and based on its strong expression in the root and shoot vasculature, could be involved in long-distance transport of Zn from the root to the shoot via the xylem.

DOI： 10.1111/j.1469-8137.2012.04144.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

In this paper, we conducted a detailed analysis of the ZIP family transporter, NcZNT1, in the zinc (Zn)/cadmium (Cd) hyperaccumulating plant species, Noccaea caerulescens, formerly known as Thlaspi caerulescens. NcZNT1 was previously suggested to be the primary root Zn/Cd uptake transporter. Both a characterization of NcZNT1 transport function in planta and in heterologous systems, and an analysis of NcZNT1 gene expression and NcZNT1 protein localization were carried out. We show that NcZNT1 is not only expressed in the root epidermis, but also is highly expressed in the root and shoot vasculature, suggesting a role in long-distance metal transport. Also, NcZNT1 was found to be a plasma membrane transporter that mediates Zn but not Cd, iron (Fe), manganese (Mn) or copper (Cu) uptake into plant cells. Two novel regions of the NcZNT1 promoter were identified which may be involved in both the hyperexpression of NcZNT1 and its ability to be regulated by plant Zn status. In conclusion, we demonstrate here that NcZNT1 plays a role in Zn and not Cd uptake from the soil, and based on its strong expression in the root and shoot vasculature, could be involved in long-distance transport of Zn from the root to the shoot via the xylem.

DOI： 10.1111/j.1469-8137.2012.04144.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Paddy rice (Oryza sativa) is able to accumulate high concentrations of Mn without showing toxicity; however, the molecular mechanisms underlying Mn uptake are unknown. Here, we report that a member of the Nramp (for the Natural Resistance-Associated Macrophage Protein) family, Nramp5, is involved in Mn uptake and subsequently the accumulation of high concentrations of Mn in rice. Nramp5 was constitutively expressed in the roots and encodes a plasma membrane-localized protein. Nramp5 was polarly localized at the distal side of both exodermis and endodermis cells. Knockout of Nramp5 resulted in a significant reduction in growth and grain yield, especially when grown at low Mn concentrations. This growth reduction could be partially rescued by supplying high concentrations of Mn but not by the addition of Fe. Mineral analysis showed that the concentration of Mn and Cd in both the roots and shoots was lower in the knockout line than in wild-type rice. A short-term uptake experiment revealed that the knockout line lost the ability to take up Mn and Cd. Taken together, Nramp5 is a major transporter of Mn and Cd and is responsible for the transport of Mn and Cd from the external solution to root cells.

DOI： 10.1105/tpc.112.096925

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

Silicon (Si) is known to be beneficial to plants, namely in alleviating biotic and abiotic stresses. The magnitude of such positive effects is associated with a plant's natural ability to absorb Si. Many grasses can accumulate as much as 10% on a dry weight basis while most dicots, including Arabidopsis, will accumulate less than 0.1%. In this report, we describe the cloning and functional characterization of TaLsi1, a wheat Si transporter gene. In addition, we developed a heterologous system for the study of Si uptake in plants by introducing TaLsi1 and OsLsi1, its ortholog in rice, into Arabidopsis, a species with a very low innate Si uptake capacity. When expressed constitutively under the control of the CaMV 35S promoter, both TaLsi1 and OsLsi1 were expressed in cells of roots and shoots. Such constitutive expression of TaLsi1 or OsLsi1 resulted in a fourfold to fivefold increase in Si accumulation in transformed plants compared to WT. However, this Si absorption caused deleterious symptoms. When the wheat transporter was expressed under the control of a root-specific promoter (a boron transporter gene (AtNIP5;1) promoter), a similar increase in Si absorption was noted but the plants did not exhibit symptoms and grew normally. These results demonstrate that TaLsi1 is indeed a functional Si transporter as its expression in Arabidopsis leads to increased Si uptake, but that this expression must be confined to root cells for healthy plant development. The availability of this heterologous expression system will facilitate further studies into the mechanisms and benefits of Si uptake.

DOI： 10.1007/s11103-012-9892-3

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Paddy rice (Oryza sativa) is able to accumulate high concentrations of Mn without showing toxicity; however, the molecular mechanisms underlying Mn uptake are unknown. Here, we report that a member of the Nramp (for the Natural Resistance-Associated Macrophage Protein) family, Nramp5, is involved in Mn uptake and subsequently the accumulation of high concentrations of Mn in rice. Nramp5 was constitutively expressed in the roots and encodes a plasma membrane-localized protein. Nramp5 was polarly localized at the distal side of both exodermis and endodermis cells. Knockout of Nramp5 resulted in a significant reduction in growth and grain yield, especially when grown at low Mn concentrations. This growth reduction could be partially rescued by supplying high concentrations of Mn but not by the addition of Fe. Mineral analysis showed that the concentration of Mn and Cd in both the roots and shoots was lower in the knockout line than in wild-type rice. A short-term uptake experiment revealed that the knockout line lost the ability to take up Mn and Cd. Taken together, Nramp5 is a major transporter of Mn and Cd and is responsible for the transport of Mn and Cd from the external solution to root cells.

DOI： 10.1105/tpc.112.096925

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

Silicon (Si) is known to be beneficial to plants, namely in alleviating biotic and abiotic stresses. The magnitude of such positive effects is associated with a plant's natural ability to absorb Si. Many grasses can accumulate as much as 10% on a dry weight basis while most dicots, including Arabidopsis, will accumulate less than 0.1%. In this report, we describe the cloning and functional characterization of TaLsi1, a wheat Si transporter gene. In addition, we developed a heterologous system for the study of Si uptake in plants by introducing TaLsi1 and OsLsi1, its ortholog in rice, into Arabidopsis, a species with a very low innate Si uptake capacity. When expressed constitutively under the control of the CaMV 35S promoter, both TaLsi1 and OsLsi1 were expressed in cells of roots and shoots. Such constitutive expression of TaLsi1 or OsLsi1 resulted in a fourfold to fivefold increase in Si accumulation in transformed plants compared to WT. However, this Si absorption caused deleterious symptoms. When the wheat transporter was expressed under the control of a root-specific promoter (a boron transporter gene (AtNIP5;1) promoter), a similar increase in Si absorption was noted but the plants did not exhibit symptoms and grew normally. These results demonstrate that TaLsi1 is indeed a functional Si transporter as its expression in Arabidopsis leads to increased Si uptake, but that this expression must be confined to root cells for healthy plant development. The availability of this heterologous expression system will facilitate further studies into the mechanisms and benefits of Si uptake.

DOI： 10.1007/s11103-012-9892-3

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記述言語：英語  

Originating from the Fertile Crescent in the Middle East, barley has now been cultivated widely on different soil types including acid soils, where aluminium toxicity is a major limiting factor. Here we show that the adaptation of barley to acid soils is achieved by the modification of a single gene (HvAACT1) encoding a citrate transporter. We find that the primary function of this protein is to release citrate from the root pericycle cells to the xylem to facilitate the translocation of iron from roots to shoots. However, a 1-kb insertion in the upstream of the HvAACT1 coding region occurring only in the Al-tolerant accessions, enhances its expression and alters the location of expression to the root tips. The altered HvAACT1 has an important role in detoxifying aluminium by secreting citrate to the rhizosphere. Thus, the insertion of a 1-kb sequence in the HvAACT1 upstream enables barley to adapt to acidic soils.

DOI： 10.1038/ncomms1726

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記述言語：英語  

Originating from the Fertile Crescent in the Middle East, barley has now been cultivated widely on different soil types including acid soils, where aluminium toxicity is a major limiting factor. Here we show that the adaptation of barley to acid soils is achieved by the modification of a single gene (HvAACT1) encoding a citrate transporter. We find that the primary function of this protein is to release citrate from the root pericycle cells to the xylem to facilitate the translocation of iron from roots to shoots. However, a 1-kb insertion in the upstream of the HvAACT1 coding region occurring only in the Al-tolerant accessions, enhances its expression and alters the location of expression to the root tips. The altered HvAACT1 has an important role in detoxifying aluminium by secreting citrate to the rhizosphere. Thus, the insertion of a 1-kb sequence in the HvAACT1 upstream enables barley to adapt to acidic soils.

DOI： 10.1038/ncomms1726

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Toxic aluminum enters the root cells rapidly, therefore internal detoxification is required. However, the molecular mechanisms underlying this process are poorly understood. Here we functionally characterized a rice gene, Os03g0755100 (OsALS1), that is regulated by ART1, a C2H2-type zinc finger transcription factor. OsALS1 encodes a half-size ABC transporter that is a member of the TAP (transporter associated with antigen processing) sub-group. Expression of OsALS1 was rapidly and specifically induced by Al in the roots, but not by other metals or low pH. OsALS1 was localized at all cells of the roots. Furthermore, OsALS1 is localized to the tonoplast. These expression patterns and cell specificity of localization are different from those of the homologous gene AtALS1 in Arabidopsis. Knockout of OsALS1 in three independent lines resulted in significant increased sensitivity to Al, but did not affect the sensitivity to other metals and low pH. Comparison of Al accumulation patterns between wild-type and osals1 mutants showed that there was no difference in Al levels in the cell sap of root tips between wild-type and the mutants, but the mutants accumulated more Al in the cytosol and nucleus than the wild-type. Expression of OsALS1 in yeast resulted in increased Al sensitivity due to mis-localization. These results indicate that OsALS1 localized at the tonoplast is responsible for sequestration of Al into the vacuoles, which is required for internal detoxification of Al in rice.

DOI： 10.1111/j.1365-313X.2011.04837.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Toxic aluminum enters the root cells rapidly, therefore internal detoxification is required. However, the molecular mechanisms underlying this process are poorly understood. Here we functionally characterized a rice gene, Os03g0755100 (OsALS1), that is regulated by ART1, a C2H2-type zinc finger transcription factor. OsALS1 encodes a half-size ABC transporter that is a member of the TAP (transporter associated with antigen processing) sub-group. Expression of OsALS1 was rapidly and specifically induced by Al in the roots, but not by other metals or low pH. OsALS1 was localized at all cells of the roots. Furthermore, OsALS1 is localized to the tonoplast. These expression patterns and cell specificity of localization are different from those of the homologous gene AtALS1 in Arabidopsis. Knockout of OsALS1 in three independent lines resulted in significant increased sensitivity to Al, but did not affect the sensitivity to other metals and low pH. Comparison of Al accumulation patterns between wild-type and osals1 mutants showed that there was no difference in Al levels in the cell sap of root tips between wild-type and the mutants, but the mutants accumulated more Al in the cytosol and nucleus than the wild-type. Expression of OsALS1 in yeast resulted in increased Al sensitivity due to mis-localization. These results indicate that OsALS1 localized at the tonoplast is responsible for sequestration of Al into the vacuoles, which is required for internal detoxification of Al in rice.

DOI： 10.1111/j.1365-313X.2011.04837.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Root outer cell layers of Oryza sativa (rice), which comprise the epidermis, exodermis and sclerenchyma, play an important role in protecting the roots from various stresses in soil, but the molecular mechanisms for the specification of these cell layers are poorly understood. In this work, we report on defective in outer cell layer specification 1 (Docs1), which is involved in the specification of outer cell layers in rice roots. Docs1 was isolated by map-based cloning using a mutant (c68) defective in the outer cell layers of primary roots. It encodes a leucine-rich repeat receptor-like kinase (LRR RLK). Docs1 mRNA was expressed in all tissues including roots, leaf blades and sheaths, and flowers. Immunostaining with an anti-Docs1 antibody showed that Docs1 was localized at the epidermis and exodermis, depending on the root region. Furthermore, Docs1 showed polar localization at the distal side. Subcellular examination showed that Docs1 was localized to the plasma membrane. Comparison of genome-wide transcriptional profiles between the wild-type and the knock-out mutant roots using microarray analysis showed that 61 and 41 genes were up- and downregulated in the mutant, including genes encoding putative transcription factors and genes potentially involved in cell wall metabolism. These results suggest that Docs1 might directly or indirectly regulate multiple genes involved in the proper development of root outer cell layers in rice.

DOI： 10.1111/j.1365-313X.2011.04824.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

Root outer cell layers of Oryza sativa (rice), which comprise the epidermis, exodermis and sclerenchyma, play an important role in protecting the roots from various stresses in soil, but the molecular mechanisms for the specification of these cell layers are poorly understood. In this work, we report on defective in outer cell layer specification 1 (Docs1), which is involved in the specification of outer cell layers in rice roots. Docs1 was isolated by map-based cloning using a mutant (c68) defective in the outer cell layers of primary roots. It encodes a leucine-rich repeat receptor-like kinase (LRR RLK). Docs1 mRNA was expressed in all tissues including roots, leaf blades and sheaths, and flowers. Immunostaining with an anti-Docs1 antibody showed that Docs1 was localized at the epidermis and exodermis, depending on the root region. Furthermore, Docs1 showed polar localization at the distal side. Subcellular examination showed that Docs1 was localized to the plasma membrane. Comparison of genome-wide transcriptional profiles between the wild-type and the knock-out mutant roots using microarray analysis showed that 61 and 41 genes were up- and downregulated in the mutant, including genes encoding putative transcription factors and genes potentially involved in cell wall metabolism. These results suggest that Docs1 might directly or indirectly regulate multiple genes involved in the proper development of root outer cell layers in rice.

DOI： 10.1111/j.1365-313X.2011.04824.x

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Chao-Feng Huang, Naoki Yamaji, Zhichang Chen, Jian Feng Ma, 2012, 'ABC transporter for Al tolerance', <i>The Plant Journal</i>, vol. 69, no. 5, pp. 857-867

DOI： 10.1111/j.1365-313x.2011.04837.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Yellow Stripe-Like (YSL) proteins belong to the oligopeptide transporter family and have been implicated in metal transport and homeostasis in different plant species. Here, we functionally characterized a rice (Oryza sativa) YSL member, OsYSL6. Knockout of OsYSL6 resulted in decreased growth of both roots and shoots only in the high-manganese (Mn) condition. There was no difference in the concentration of total Mn and other essential metals between the wild-type rice and the knockout line, but the knockout line showed a higher Mn concentration in the leaf apoplastic solution and a lower Mn concentration in the symplastic solution than wild-type rice. OsYSL6 was constitutively expressed in both the shoots and roots, and the expression level was not affected by either deficiency or toxicity of various metals. Furthermore, the expression level increased with leaf age. Analysis with OsYSL6 promoter-green fluorescent protein transgenic rice revealed that OsYSL6 was expressed in all cells of both the roots and shoots. Heterogolous expression of OsYSL6 in yeast showed transport activity for the Mn-nicotianamine complex but not for the Mn-mugineic acid complex. Taken together, our results suggest that OsYSL6 is a Mn-nicotianamine transporter that is required for the detoxification of excess Mn in rice.

DOI： 10.1104/pp.111.186031

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

A number of plant species, including rice, secretes citrate from roots in response to Al stress. Here we characterized the functions of a gene, OsFRDL4 (Os01g0919100) that belongs to the multidrug and toxic compound extrusion (MATE) family in rice (Oryza sativa). Heterologous expression in Xenopus oocyte showed that the OsFRDL4 protein was able to transport citrate and was activated by Al. The expression level of the OsFRDL4 gene in roots was very low in the absence of Al, but was greatly enhanced by Al after short exposure. Furthermore, the OsFRDL4 expression was regulated by ART1, a C2H2-type zinc finger transcription factor for Al tolerance. Transient expression of OsFRDL4 in onion epidermal cells showed that it localized to the plasma membrane. Immunostaining showed that OsFRDL4 was localized in all cells in the root tip. These expression patterns and cell specificity of localization of OsFRDL4 are different from other MATE members identified previously. Knockout of OsFRDL4 resulted in decreased Al tolerance and decreased citrate secretion compared with the wild-type rice, but did not affect citrate concentration in the xylem sap. Furthermore, there is a positive correlation between OsFRDL4 expression level and the amount of citrate secretion in rice cultivars that are differing in Al tolerance. Taken together, our results show that OsFRDL4 is an Al-induced citrate transporter localized at the plasma membrane of rice root cells and is one of the components of high Al tolerance in rice.

DOI： 10.1111/j.1365-313X.2011.04757.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Yellow Stripe-Like (YSL) proteins belong to the oligopeptide transporter family and have been implicated in metal transport and homeostasis in different plant species. Here, we functionally characterized a rice (Oryza sativa) YSL member, OsYSL6. Knockout of OsYSL6 resulted in decreased growth of both roots and shoots only in the high-manganese (Mn) condition. There was no difference in the concentration of total Mn and other essential metals between the wild-type rice and the knockout line, but the knockout line showed a higher Mn concentration in the leaf apoplastic solution and a lower Mn concentration in the symplastic solution than wild-type rice. OsYSL6 was constitutively expressed in both the shoots and roots, and the expression level was not affected by either deficiency or toxicity of various metals. Furthermore, the expression level increased with leaf age. Analysis with OsYSL6 promoter-green fluorescent protein transgenic rice revealed that OsYSL6 was expressed in all cells of both the roots and shoots. Heterogolous expression of OsYSL6 in yeast showed transport activity for the Mn-nicotianamine complex but not for the Mn-mugineic acid complex. Taken together, our results suggest that OsYSL6 is a Mn-nicotianamine transporter that is required for the detoxification of excess Mn in rice.

DOI： 10.1104/pp.111.186031

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

A number of plant species, including rice, secretes citrate from roots in response to Al stress. Here we characterized the functions of a gene, OsFRDL4 (Os01g0919100) that belongs to the multidrug and toxic compound extrusion (MATE) family in rice (Oryza sativa). Heterologous expression in Xenopus oocyte showed that the OsFRDL4 protein was able to transport citrate and was activated by Al. The expression level of the OsFRDL4 gene in roots was very low in the absence of Al, but was greatly enhanced by Al after short exposure. Furthermore, the OsFRDL4 expression was regulated by ART1, a C2H2-type zinc finger transcription factor for Al tolerance. Transient expression of OsFRDL4 in onion epidermal cells showed that it localized to the plasma membrane. Immunostaining showed that OsFRDL4 was localized in all cells in the root tip. These expression patterns and cell specificity of localization of OsFRDL4 are different from other MATE members identified previously. Knockout of OsFRDL4 resulted in decreased Al tolerance and decreased citrate secretion compared with the wild-type rice, but did not affect citrate concentration in the xylem sap. Furthermore, there is a positive correlation between OsFRDL4 expression level and the amount of citrate secretion in rice cultivars that are differing in Al tolerance. Taken together, our results show that OsFRDL4 is an Al-induced citrate transporter localized at the plasma membrane of rice root cells and is one of the components of high Al tolerance in rice.

DOI： 10.1111/j.1365-313X.2011.04757.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The plant cuticle, a cutin matrix embedded with and covered by wax, seals the aerial organ's surface to protect the plant against uncontrolled water loss. The cutin matrix is essential for the cuticle to function as a barrier to water loss. Recently, we identified from wild barley a drought supersensitive mutant, eibi1, which is caused by a defective cutin matrix as the result of the loss of function of HvABCG31, an ABCG full transporter. Here, we report that eibi1 epidermal cells contain lipid-like droplets, which are supposed to consist of cutin monomers that have not been transported out of the cells. The eibi1 cuticle is fragile due to a defective cutin matrix. The rice ortholog of the EIBI1 gene has a similar pattern of expression, young shoot but not flag leaf blade, as the barley gene. The model of the function of Eibi1 is discussed. The HvABCG31 full transporter functions in the export of cutin components and contributed to land plant colonization, hence also to terrestrial life evolution. © 2011 Landes Bioscience.

DOI： 10.4161/psb.6.9.17507

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Nodulin-26-like intrinsic proteins (NIPs) of the aquaporin family are involved in the transport of diverse solutes, but the mechanisms controlling the selectivity of transport substrates are poorly understood. The purpose of this study was to investigate how the aromatic/arginine (ar/R) selectivity filter influences the substrate selectivity of two NIP aquaporins; the silicic acid (Si) transporter OsLsi1 (OsNIP2;1) from rice and the boric acid (B) transporter AtNIP5;1 from Arabidopsis; both proteins are also permeable to arsenite. Native and site-directed mutagenized variants of the two genes were expressed in Xenopus oocytes and the transport activities for Si, B, arsenite, and water were assayed. Substitution of the amino acid at the ar/R second helix (H2) position of OsLsi1 did not affect the transport activities for Si, B, and arsenite, but that at the H5 position resulted in a total loss of Si and B transport activities and a partial loss of arsenite transport activity. Conversely, changes of the AtNIP5;1 ar/R selectivity filter and the NPA motifs to the OsLsi1 type did not result in a gain of Si transport activity. B transport activity was partially lost in the H5 mutant but unaffected in the H2 mutant of AtNIP5;1. In contrast, both the single and double mutations at the H2 and/or H5 positions of AtNIP5;1 did not affect arsenite transport activity. The results reveal that the residue at the H5 position of the ar/R filter of both OsLsi1 and AtNIP5;1 plays a key role in the permeability to Si and B, but there is a relatively low selectivity for arsenite.

DOI： 10.1093/jxb/err158

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Nodulin-26-like intrinsic proteins (NIPs) of the aquaporin family are involved in the transport of diverse solutes, but the mechanisms controlling the selectivity of transport substrates are poorly understood. The purpose of this study was to investigate how the aromatic/arginine (ar/R) selectivity filter influences the substrate selectivity of two NIP aquaporins; the silicic acid (Si) transporter OsLsi1 (OsNIP2;1) from rice and the boric acid (B) transporter AtNIP5;1 from Arabidopsis; both proteins are also permeable to arsenite. Native and site-directed mutagenized variants of the two genes were expressed in Xenopus oocytes and the transport activities for Si, B, arsenite, and water were assayed. Substitution of the amino acid at the ar/R second helix (H2) position of OsLsi1 did not affect the transport activities for Si, B, and arsenite, but that at the H5 position resulted in a total loss of Si and B transport activities and a partial loss of arsenite transport activity. Conversely, changes of the AtNIP5;1 ar/R selectivity filter and the NPA motifs to the OsLsi1 type did not result in a gain of Si transport activity. B transport activity was partially lost in the H5 mutant but unaffected in the H2 mutant of AtNIP5;1. In contrast, both the single and double mutations at the H2 and/or H5 positions of AtNIP5;1 did not affect arsenite transport activity. The results reveal that the residue at the H5 position of the ar/R filter of both OsLsi1 and AtNIP5;1 plays a key role in the permeability to Si and B, but there is a relatively low selectivity for arsenite.

DOI： 10.1093/jxb/err158

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記述言語：英語   出版者・発行元：JAPAN ACAD  

Silicon (Si) is the most abundant minerals in soil and exerts beneficial effects on plant growth by alleviating various stresses. The transport of Si from soil to the panicles is mediated by different transporters. Lsi1, belonging to a NIP group of the aquaporin family, is responsible for the uptake of Si from soil into the root cells in both dicots and monocots although its expression patterns and cellular localization differ with plant species. The subsequent transport of Si out of the root cells towards the stele is medicated by an active efflux transporter, Lsi2. Lsi1. and Lsi2 are polarly localized at the distal and proximal sides, respectively, of both exodermis and endodermis in rice root. Silicon in the xylem sap is presented in the form of monosilicic acid and is unloaded by Lsi6, a homolog of Lsi1 in rice. Lsi6 is also involved in the inter-vascular transfer of Si at the node, which is necessary for preferential Si distribution to the panicles.

DOI： 10.2183/pjab.87.377

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Land plants have developed a cuticle preventing uncontrolled water loss. Here we report that an ATP-binding cassette (ABC) subfamily G (ABCG) full transporter is required for leaf water conservation in both wild barley and rice. A spontaneous mutation, eibi1.b, in wild barley has a low capacity to retain leaf water, a phenotype associated with reduced cutin deposition and a thin cuticle. Map-based cloning revealed that Eibi1 encodes an HvABCG31 full transporter. The gene was highly expressed in the elongation zone of a growing leaf (the site of cutin synthesis), and its gene product also was localized in developing, but not in mature tissue. A de novo wild barley mutant named "eibi1.c," along with two transposon insertion lines of rice mutated in the ortholog of HvABCG31 also were unable to restrict water loss from detached leaves. HvABCG31 is hypothesized to function as a transporter involved in cutin formation. Homologs of HvABCG31 were found in green algae, moss, and lycopods, indicating that this full transporter is highly conserved in the evolution of land plants.

DOI： 10.1073/pnas.1108444108

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Land plants have developed a cuticle preventing uncontrolled water loss. Here we report that an ATP-binding cassette (ABC) subfamily G (ABCG) full transporter is required for leaf water conservation in both wild barley and rice. A spontaneous mutation, eibi1.b, in wild barley has a low capacity to retain leaf water, a phenotype associated with reduced cutin deposition and a thin cuticle. Map-based cloning revealed that Eibi1 encodes an HvABCG31 full transporter. The gene was highly expressed in the elongation zone of a growing leaf (the site of cutin synthesis), and its gene product also was localized in developing, but not in mature tissue. A de novo wild barley mutant named "eibi1.c," along with two transposon insertion lines of rice mutated in the ortholog of HvABCG31 also were unable to restrict water loss from detached leaves. HvABCG31 is hypothesized to function as a transporter involved in cutin formation. Homologs of HvABCG31 were found in green algae, moss, and lycopods, indicating that this full transporter is highly conserved in the evolution of land plants.

DOI： 10.1073/pnas.1108444108

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記述言語：英語   出版者・発行元：JAPAN ACAD  

Silicon (Si) is the most abundant minerals in soil and exerts beneficial effects on plant growth by alleviating various stresses. The transport of Si from soil to the panicles is mediated by different transporters. Lsi1, belonging to a NIP group of the aquaporin family, is responsible for the uptake of Si from soil into the root cells in both dicots and monocots although its expression patterns and cellular localization differ with plant species. The subsequent transport of Si out of the root cells towards the stele is medicated by an active efflux transporter, Lsi2. Lsi1. and Lsi2 are polarly localized at the distal and proximal sides, respectively, of both exodermis and endodermis in rice root. Silicon in the xylem sap is presented in the form of monosilicic acid and is unloaded by Lsi6, a homolog of Lsi1 in rice. Lsi6 is also involved in the inter-vascular transfer of Si at the node, which is necessary for preferential Si distribution to the panicles.

DOI： 10.2183/pjab.87.377

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記述言語：英語   出版者・発行元：JAPAN ACAD  

Silicon (Si) is the most abundant minerals in soil and exerts beneficial effects on plant growth by alleviating various stresses. The transport of Si from soil to the panicles is mediated by different transporters. Lsi1, belonging to a NIP group of the aquaporin family, is responsible for the uptake of Si from soil into the root cells in both dicots and monocots although its expression patterns and cellular localization differ with plant species. The subsequent transport of Si out of the root cells towards the stele is medicated by an active efflux transporter, Lsi2. Lsi1. and Lsi2 are polarly localized at the distal and proximal sides, respectively, of both exodermis and endodermis in rice root. Silicon in the xylem sap is presented in the form of monosilicic acid and is unloaded by Lsi6, a homolog of Lsi1 in rice. Lsi6 is also involved in the inter-vascular transfer of Si at the node, which is necessary for preferential Si distribution to the panicles.

DOI： 10.2183/pjab.87.377

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) is one of the most aluminum (Al)-tolerant species among small-grain cereals. Recent identification of a transcription factor AL RESISTANCE TRANSCRIPTION FACTOR1 (ART1) revealed that this high Al tolerance in rice is achieved by multiple genes involved in detoxification of Al at different cellular levels. ART1 is a C2H2-type zinc-finger transcription factor and regulates the expression of 31 genes in the downstream. In this study, we attempted to identify a cis-acting element of ART1. We used the promoter region of SENSITIVE TO AL RHIZOTOXICITY1, an Al tolerance gene in the downstream of ART1. With the help of gel-shift assay, we were able to identify the cis-acting element as GGN(T/g/a/C)V(C/A/g)S(C/G). This element was found in the promoter region of 29 genes among 31 ART1-regulated genes. To confirm this cis-acting element in vivo, we transiently introduced this element one or five times tandemly repeated sequence with 35S minimal promoter and green fluorescent protein reporter together with or without ART1 gene in the tobacco (Nicotiana tabacum) mesophyll protoplasts. The results showed that the expression of green fluorescent protein reporter responded to ART1 expression. Furthermore, the expression increased with repetition of the cis-acting element. Our results indicate that the five nucleotides identified are the target DNA-binding sequence of ART1.

DOI： 10.1104/pp.111.175802

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

P>Cadmium (Cd) is a highly toxic heavy metal for plants, but several unique Cd-hyperaccumulating plant species are able to accumulate this metal to extraordinary concentrations in the aboveground tissues without showing any toxic symptoms. However, the molecular mechanisms underlying this hypertolerance to Cd are poorly understood. Here we have isolated and functionally characterized an allelic gene, TcHMA3 (heavy metal ATPase 3) from two ecotypes (Ganges and Prayon) of Thlaspi caerulescens contrasting in Cd accumulation and tolerance. The TcHMA3 alleles from the higher (Ganges) and lower Cd-accumulating ecotype (Prayon) share 97.8% identity, and encode a P(1B)-type ATPase. There were no differences in the expression pattern, cell-specificity of protein localization and transport substrate-specificity of TcHMA3 between the two ecotypes. Both alleles were characterized by constitutive expression in the shoot and root, a tonoplast localization of the protein in all leaf cells and specific transport activity for Cd. The only difference between the two ecotypes was the expression level of TcHMA3: Ganges showed a sevenfold higher expression than Prayon, partly caused by a higher copy number. Furthermore, the expression level and localization of TcHMA3 were different from AtHMA3 expression in Arabidopsis. Overexpression of TcHMA3 in Arabidopsis significantly enhanced tolerance to Cd and slightly increased tolerance to Zn, but did not change Co or Pb tolerance. These results indicate that TcHMA3 is a tonoplast-localized transporter highly specific for Cd, which is responsible for sequestration of Cd into the leaf vacuoles, and that a higher expression of this gene is required for Cd hypertolerance in the Cd-hyperaccumulating ecotype of T. caerulescens.

DOI： 10.1111/j.1365-313X.2011.04548.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

P>Cadmium (Cd) is a highly toxic heavy metal for plants, but several unique Cd-hyperaccumulating plant species are able to accumulate this metal to extraordinary concentrations in the aboveground tissues without showing any toxic symptoms. However, the molecular mechanisms underlying this hypertolerance to Cd are poorly understood. Here we have isolated and functionally characterized an allelic gene, TcHMA3 (heavy metal ATPase 3) from two ecotypes (Ganges and Prayon) of Thlaspi caerulescens contrasting in Cd accumulation and tolerance. The TcHMA3 alleles from the higher (Ganges) and lower Cd-accumulating ecotype (Prayon) share 97.8% identity, and encode a P(1B)-type ATPase. There were no differences in the expression pattern, cell-specificity of protein localization and transport substrate-specificity of TcHMA3 between the two ecotypes. Both alleles were characterized by constitutive expression in the shoot and root, a tonoplast localization of the protein in all leaf cells and specific transport activity for Cd. The only difference between the two ecotypes was the expression level of TcHMA3: Ganges showed a sevenfold higher expression than Prayon, partly caused by a higher copy number. Furthermore, the expression level and localization of TcHMA3 were different from AtHMA3 expression in Arabidopsis. Overexpression of TcHMA3 in Arabidopsis significantly enhanced tolerance to Cd and slightly increased tolerance to Zn, but did not change Co or Pb tolerance. These results indicate that TcHMA3 is a tonoplast-localized transporter highly specific for Cd, which is responsible for sequestration of Cd into the leaf vacuoles, and that a higher expression of this gene is required for Cd hypertolerance in the Cd-hyperaccumulating ecotype of T. caerulescens.

DOI： 10.1111/j.1365-313X.2011.04548.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) is one of the most aluminum (Al)-tolerant species among small-grain cereals. Recent identification of a transcription factor AL RESISTANCE TRANSCRIPTION FACTOR1 (ART1) revealed that this high Al tolerance in rice is achieved by multiple genes involved in detoxification of Al at different cellular levels. ART1 is a C2H2-type zinc-finger transcription factor and regulates the expression of 31 genes in the downstream. In this study, we attempted to identify a cis-acting element of ART1. We used the promoter region of SENSITIVE TO AL RHIZOTOXICITY1, an Al tolerance gene in the downstream of ART1. With the help of gel-shift assay, we were able to identify the cis-acting element as GGN(T/g/a/C)V(C/A/g)S(C/G). This element was found in the promoter region of 29 genes among 31 ART1-regulated genes. To confirm this cis-acting element in vivo, we transiently introduced this element one or five times tandemly repeated sequence with 35S minimal promoter and green fluorescent protein reporter together with or without ART1 gene in the tobacco (Nicotiana tabacum) mesophyll protoplasts. The results showed that the expression of green fluorescent protein reporter responded to ART1 expression. Furthermore, the expression increased with repetition of the cis-acting element. Our results indicate that the five nucleotides identified are the target DNA-binding sequence of ART1.

DOI： 10.1104/pp.111.175802

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記述言語：英語  

Yellow stripe-like (YSL) family transporters, belonging to a novel subfamily of oligopeptide transporter (OPT), has been proposed to be involved in metal uptake and long-distance transport, but only a few of them have been functionally characterized so far. In the present study, we isolated an uncharacterized member of the YSL family, HvYSL5, in barley based on expressed sequence tag (EST) information. HvYSL5 shared 50% identity with HvYS1, a transporter for the ferric-mugineic acid complex, at the amino acid level. Promoter analysis showed that the HvYSL5 upstream sequence contains both iron deficiency response element 1 and 2 (IDE1 and 2). HvYSL5 was expressed in the roots and the expression was greatly induced by Fe deficiency, but not by deficiency of other metals including Zn, Cu and Mn. Spatial investigation showed that much higher expression of HvYSL5 was found in the mature zones of the roots, but not in the root tips. Furthermore, the expression showed a diurnal rhythm, being the highest in the morning, but with no expression in the afternoon. HvYSL5 was localized in all root cells, and subcellular localization analysis showed that HvYSL5 is likely to be localized in the vesicles. Knockdown of HvYSL5 did not result in any detectable phenotype changes. Although the exact role of HvYSL5 remains to be examined, our results suggest that it is involved in the transient storage of Fe or phytosiderophores.

DOI： 10.1093/pcp/pcr009

PubMed

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記述言語：英語  

Yellow stripe-like (YSL) family transporters, belonging to a novel subfamily of oligopeptide transporter (OPT), has been proposed to be involved in metal uptake and long-distance transport, but only a few of them have been functionally characterized so far. In the present study, we isolated an uncharacterized member of the YSL family, HvYSL5, in barley based on expressed sequence tag (EST) information. HvYSL5 shared 50% identity with HvYS1, a transporter for the ferric-mugineic acid complex, at the amino acid level. Promoter analysis showed that the HvYSL5 upstream sequence contains both iron deficiency response element 1 and 2 (IDE1 and 2). HvYSL5 was expressed in the roots and the expression was greatly induced by Fe deficiency, but not by deficiency of other metals including Zn, Cu and Mn. Spatial investigation showed that much higher expression of HvYSL5 was found in the mature zones of the roots, but not in the root tips. Furthermore, the expression showed a diurnal rhythm, being the highest in the morning, but with no expression in the afternoon. HvYSL5 was localized in all root cells, and subcellular localization analysis showed that HvYSL5 is likely to be localized in the vesicles. Knockdown of HvYSL5 did not result in any detectable phenotype changes. Although the exact role of HvYSL5 remains to be examined, our results suggest that it is involved in the transient storage of Fe or phytosiderophores.

DOI： 10.1093/pcp/pcr009

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

High silicon (Si) accumulation is required for high and sustainable production of rice. The uptake of Si by rice roots is mediated by both influx transporter Lsi1 and efflux transporter Lsi2. Here we further characterized Lsi2 in terms of localization and expression patterns. Analysis with promoter-GFP transgenic rice revealed that Lsi2 was expressed in the main and lateral roots, but not in the root hairs. In lateral roots, Lsi2 was localized at the proximal side of both exodermis and endodermis like main roots. The expression of Lsi2 gene was down-regulated by Si in the wild-type rice, but unaffected in the lsi2 mutant, suggesting that the expression of Lsi2 is regulated by Si accumulated in the shoots. Treatment with drought and abscisic acid rapidly resulted in decreased Lsi2 expression. Monitoring of Lsi2 expression at different growth stage showed a transient increase around the heading stage in rice grown in a paddy field. These expression patterns are similar to those of Lsi1, indicating that Lsi2 is co-regulated with Lsi1 and the expression of these two genes responds to both environmental condition and plant Si requirement.

DOI： 10.1080/00380768.2011.565480

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

P>A high accumulation of silicon (Si) is required for overcoming abiotic and biotic stresses, but the molecular mechanisms of Si uptake, especially in dicotyledonous species, is poorly understood. Herein, we report the identification of an influx transporter of Si in two Cucurbita moschata (pumpkin) cultivars greatly differing in Si accumulation, which are used for the rootstocks of bloom and bloomless Cucumis sativus (cucumber), respectively. Heterogeneous expression in both Xenopus oocytes and rice mutant defective in Si uptake showed that the influx transporter from the bloom pumpkin rootstock can transport Si, whereas that from the bloomless rootstock cannot. Analysis with site-directed mutagenesis showed that, among the two amino acid residues differing between the two types of rootstocks, only changing a proline to a leucine at position 242 results in the loss of Si transport activity. Furthermore, all pumpkin cultivars for bloomless rootstocks tested have this mutation. The transporter is localized in all cells of the roots, and investigation of the subcellular localization with different approaches consistently showed that the influx Si transporter from the bloom pumpkin rootstock was localized at the plasma membrane, whereas the one from the bloomless rootstock was localized at the endoplasmic reticulum. Taken together, our results indicate that the difference in Si uptake between two pumpkin cultivars is probably the result of allelic variation in one amino acid residue of the Si influx transporter, which affects the subcellular localization and subsequent transport of Si from the external solution to the root cells.

DOI： 10.1111/j.1365-313X.2011.04483.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

P>A high accumulation of silicon (Si) is required for overcoming abiotic and biotic stresses, but the molecular mechanisms of Si uptake, especially in dicotyledonous species, is poorly understood. Herein, we report the identification of an influx transporter of Si in two Cucurbita moschata (pumpkin) cultivars greatly differing in Si accumulation, which are used for the rootstocks of bloom and bloomless Cucumis sativus (cucumber), respectively. Heterogeneous expression in both Xenopus oocytes and rice mutant defective in Si uptake showed that the influx transporter from the bloom pumpkin rootstock can transport Si, whereas that from the bloomless rootstock cannot. Analysis with site-directed mutagenesis showed that, among the two amino acid residues differing between the two types of rootstocks, only changing a proline to a leucine at position 242 results in the loss of Si transport activity. Furthermore, all pumpkin cultivars for bloomless rootstocks tested have this mutation. The transporter is localized in all cells of the roots, and investigation of the subcellular localization with different approaches consistently showed that the influx Si transporter from the bloom pumpkin rootstock was localized at the plasma membrane, whereas the one from the bloomless rootstock was localized at the endoplasmic reticulum. Taken together, our results indicate that the difference in Si uptake between two pumpkin cultivars is probably the result of allelic variation in one amino acid residue of the Si influx transporter, which affects the subcellular localization and subsequent transport of Si from the external solution to the root cells.

DOI： 10.1111/j.1365-313X.2011.04483.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Cadmium (Cd) in rice is a major source of Cd intake for people on a staple rice diet. The mechanisms underlying Cd accumulation in rice plant are still poorly understood. Here, we characterized the physiology and genetics of Cd transport in a high-Cd-accumulating cultivar (Jarjan) of rice (Oryza sativa). Jarjan showed 5- to 34-fold higher Cd accumulation in the shoots and grains than the cultivar Nipponbare, when it was grown in either a non-Cd-contaminated or a Cd-contaminated soil. A short-term uptake experiment showed no significant difference in Cd uptake by the roots between the two cultivars. However, Jarjan translocated 49% of the total Cd taken up to the shoots, whereas Nipponbare retained most of the Cd in the roots. In both concentration- and time-dependent experiments, Jarjan showed a superior capacity for root-to-shoot translocation of Cd. These results indicate that the high-Cd-accumulation phenotype in Jarjan results from efficient translocation of Cd from roots to shoots. Genetic analysis using an F(2) population derived from Jarjan and Nipponbare revealed that plants showing high- and low-Cd-accumulation phenotypes segregated in a 1:3 ratio, indicating that high accumulation in Jarjan is controlled by a single recessive gene. Furthermore, we isolated OsHMA3, a gene encoding a tonoplast-localized Cd transporter from Jarjan. The OsHMA3 protein was localized in all roots cells, but the sequence has a mutation leading to loss of function. Therefore, failure to sequester Cd into the root vacuoles by OsHMA3 is probably responsible for high Cd accumulation in Jarjan.

DOI： 10.1093/jxb/erq383

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Cadmium (Cd) in rice is a major source of Cd intake for people on a staple rice diet. The mechanisms underlying Cd accumulation in rice plant are still poorly understood. Here, we characterized the physiology and genetics of Cd transport in a high-Cd-accumulating cultivar (Jarjan) of rice (Oryza sativa). Jarjan showed 5- to 34-fold higher Cd accumulation in the shoots and grains than the cultivar Nipponbare, when it was grown in either a non-Cd-contaminated or a Cd-contaminated soil. A short-term uptake experiment showed no significant difference in Cd uptake by the roots between the two cultivars. However, Jarjan translocated 49% of the total Cd taken up to the shoots, whereas Nipponbare retained most of the Cd in the roots. In both concentration- and time-dependent experiments, Jarjan showed a superior capacity for root-to-shoot translocation of Cd. These results indicate that the high-Cd-accumulation phenotype in Jarjan results from efficient translocation of Cd from roots to shoots. Genetic analysis using an F(2) population derived from Jarjan and Nipponbare revealed that plants showing high- and low-Cd-accumulation phenotypes segregated in a 1:3 ratio, indicating that high accumulation in Jarjan is controlled by a single recessive gene. Furthermore, we isolated OsHMA3, a gene encoding a tonoplast-localized Cd transporter from Jarjan. The OsHMA3 protein was localized in all roots cells, but the sequence has a mutation leading to loss of function. Therefore, failure to sequester Cd into the root vacuoles by OsHMA3 is probably responsible for high Cd accumulation in Jarjan.

DOI： 10.1093/jxb/erq383

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

High silicon (Si) accumulation is required for high and sustainable production of rice. The uptake of Si by rice roots is mediated by both influx transporter Lsi1 and efflux transporter Lsi2. Here we further characterized Lsi2 in terms of localization and expression patterns. Analysis with promoter-GFP transgenic rice revealed that Lsi2 was expressed in the main and lateral roots, but not in the root hairs. In lateral roots, Lsi2 was localized at the proximal side of both exodermis and endodermis like main roots. The expression of Lsi2 gene was down-regulated by Si in the wild-type rice, but unaffected in the lsi2 mutant, suggesting that the expression of Lsi2 is regulated by Si accumulated in the shoots. Treatment with drought and abscisic acid rapidly resulted in decreased Lsi2 expression. Monitoring of Lsi2 expression at different growth stage showed a transient increase around the heading stage in rice grown in a paddy field. These expression patterns are similar to those of Lsi1, indicating that Lsi2 is co-regulated with Lsi1 and the expression of these two genes responds to both environmental condition and plant Si requirement.

DOI： 10.1080/00380768.2011.565480

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

High silicon (Si) accumulation is required for high and sustainable production of rice. The uptake of Si by rice roots is mediated by both influx transporter Lsi1 and efflux transporter Lsi2. Here we further characterized Lsi2 in terms of localization and expression patterns. Analysis with promoter-GFP transgenic rice revealed that Lsi2 was expressed in the main and lateral roots, but not in the root hairs. In lateral roots, Lsi2 was localized at the proximal side of both exodermis and endodermis like main roots. The expression of Lsi2 gene was down-regulated by Si in the wild-type rice, but unaffected in the lsi2 mutant, suggesting that the expression of Lsi2 is regulated by Si accumulated in the shoots. Treatment with drought and abscisic acid rapidly resulted in decreased Lsi2 expression. Monitoring of Lsi2 expression at different growth stage showed a transient increase around the heading stage in rice grown in a paddy field. These expression patterns are similar to those of Lsi1, indicating that Lsi2 is co-regulated with Lsi1 and the expression of these two genes responds to both environmental condition and plant Si requirement. © 2011 Japanese Society of Soil Science and Plant Nutrition.

DOI： 10.1080/00380768.2011.565480

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Jixing Xia, Naoki Yamaji, Jian Feng Ma, 2011, 'Further characterization of an aluminum influx transporter in rice', <i>Plant Signaling & Behavior</i>, vol. 6, no. 1, pp. 160-163

DOI： 10.4161/psb.6.1.14319

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Aluminum (Al) is the most abundant metal in the Earth's crust, but its trivalent ionic form is highly toxic to all organisms at low concentrations. How Al enters cells has not been elucidated in any organisms. Herein, we report a transporter, Nrat1 (Nramp aluminum transporter 1), specific for trivalent Al ion in rice. Nrat1 belongs to the Nramp (natural resistance-associated macrophage protein) family, but shares a low similarity with other Nramp members. When expressed in yeast, Nrat1 transports trivalent Al ion, but not other divalent ions, such as manganese, iron, and cadmium, or the Al-citrate complex. Nrat1 is localized at the plasma membranes of all cells of root tips except epidermal cells. Knockout of Nrat1 resulted in decreased Al uptake, increased Al binding to cell wall, and enhanced Al sensitivity, but did not affect the tolerance to other metals. Expression of Nrat1 is up-regulated by Al in the roots and regulated by a C2H2 zinc finger transcription factor (ART1). We therefore concluded that Nrat1 is a plasma membrane-localized transporter for trivalent Al, which is required for a prior step of final Al detoxification through sequestration of Al into vacuoles.

DOI： 10.1073/pnas.1004949107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Aluminum (Al) is the most abundant metal in the Earth's crust, but its trivalent ionic form is highly toxic to all organisms at low concentrations. How Al enters cells has not been elucidated in any organisms. Herein, we report a transporter, Nrat1 (Nramp aluminum transporter 1), specific for trivalent Al ion in rice. Nrat1 belongs to the Nramp (natural resistance-associated macrophage protein) family, but shares a low similarity with other Nramp members. When expressed in yeast, Nrat1 transports trivalent Al ion, but not other divalent ions, such as manganese, iron, and cadmium, or the Al-citrate complex. Nrat1 is localized at the plasma membranes of all cells of root tips except epidermal cells. Knockout of Nrat1 resulted in decreased Al uptake, increased Al binding to cell wall, and enhanced Al sensitivity, but did not affect the tolerance to other metals. Expression of Nrat1 is up-regulated by Al in the roots and regulated by a C2H2 zinc finger transcription factor (ART1). We therefore concluded that Nrat1 is a plasma membrane-localized transporter for trivalent Al, which is required for a prior step of final Al detoxification through sequestration of Al into vacuoles.

DOI： 10.1073/pnas.1004949107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Intake of toxic cadmium (Cd) from rice caused Itai-itai disease in the past and it is still a threat for human health. Therefore, control of the accumulation of Cd from soil is an important food-safety issue, but the molecular mechanism for the control is unknown. Herein, we report a gene (OsHMA3) responsible for low Cd accumulation in rice that was isolated from a mapping population derived from a cross between a high and low Cd-accumulating cultivar. The gene encodes a transporter belonging to the P(1B)-type ATPase family, but shares low similarity with other members. Heterologous expression in yeast showed that the transporter from the low-Cd cultivar is functional, but the transporter from the high-Cd cultivar had lost its function, probably because of the single amino acid mutation. The transporter is mainly expressed in the tonoplast of root cells at a similar level in both the low and high Cd-accumulating cultivars. Overexpression of the functional gene from the low Cd-accumulating cultivar selectively decreased accumulation of Cd, but not other micronutrients in the grain. Our results indicated that OsHMA3 from the low Cd-accumulating cultivar limits translocation of Cd from the roots to the above-ground tissues by selectively sequestrating Cd into the root vacuoles.

DOI： 10.1073/pnas.1005396107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Intake of toxic cadmium (Cd) from rice caused Itai-itai disease in the past and it is still a threat for human health. Therefore, control of the accumulation of Cd from soil is an important food-safety issue, but the molecular mechanism for the control is unknown. Herein, we report a gene (OsHMA3) responsible for low Cd accumulation in rice that was isolated from a mapping population derived from a cross between a high and low Cd-accumulating cultivar. The gene encodes a transporter belonging to the P(1B)-type ATPase family, but shares low similarity with other members. Heterologous expression in yeast showed that the transporter from the low-Cd cultivar is functional, but the transporter from the high-Cd cultivar had lost its function, probably because of the single amino acid mutation. The transporter is mainly expressed in the tonoplast of root cells at a similar level in both the low and high Cd-accumulating cultivars. Overexpression of the functional gene from the low Cd-accumulating cultivar selectively decreased accumulation of Cd, but not other micronutrients in the grain. Our results indicated that OsHMA3 from the low Cd-accumulating cultivar limits translocation of Cd from the roots to the above-ground tissues by selectively sequestrating Cd into the root vacuoles.

DOI： 10.1073/pnas.1005396107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

ATP-binding cassette (ABC) transporters represent a large family in plants, but the functions of most of these transporters are unknown. Here we report a gene, AtSTAR1, only encoding an ATP-binding domain of a bacterial-type ABC transporter in Arabidopsis (Arabidopsis thaliana). AtSTAR1 is an ortholog of rice (Oryza sativa) OsSTAR1, which has been implicated in aluminum (Al) tolerance. Knockout of AtSTAR1 resulted in increased sensitivity to Al and earlier flowering. Unlike OsSTAR1, AtSTAR1 was expressed in both the roots and shoots and its expression was not induced by Al or other stresses. Investigation of tissue-specific localization of AtSTAR1 through beta-glucuronidase fusion revealed that AtSTAR1 was predominantly expressed at outer cell layers of root tips and developing leaves, whose localization is also different from those of OsSTAR1. However, introduction of OsSTAR1 into atstar1 mutant rescued the sensitivity of atstar1 to Al, indicating that AtSTAR1 has a similar function as OsSTAR1. Furthermore, we found that AtSTAR1 may interact with ALS3, a transmembrane-binding domain in Arabidopsis to form a complex because introduction of OsSTAR1, a functional substitute of AtSTAR1, into als3 mutant resulted in the loss of OsSTAR1 protein. All these findings indicate that AtSTAR1 is involved in the basic detoxification of Al in Arabidopsis.

DOI： 10.1104/pp.110.155028

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) as a staple food, provides a major source of dietary selenium (Se) for humans, which essentially requires Se, however, the molecular mechanism for Se uptake is still poorly understood. Herein, we show evidence that the uptake of selenite, a main bioavailable form of Se in paddy soils, is mediated by a silicon (Si) influx transporter Lsi1 (OsNIP2;1) in rice. Defect of OsNIP2;1 resulted in a significant decrease in the Se concentration of the shoots and xylem sap when selenite was given. However, there was no difference in the Se concentration between the wild-type rice and mutant of OsNIP2;1 when selenate was supplied. A short-term uptake experiment showed that selenite uptake greatly increased with decreasing pH in the external solution. Si as silicic acid did not inhibit the Se uptake from selenite in both rice and yeast (Saccharomyces cerevisiae) at low pHs. Expression of OsNIP2;1 in yeast enhanced the selenite uptake at pH 3.5 and 5.5 but not at pH 7.5. On the other hand, defect of Si efflux transporter Lsi2 did not affect the uptake of Se either from selenite or selenate. Taken together, our results indicate that Si influx transporter OsNIP2;1 is permeable to selenite.

DOI： 10.1104/pp.110.157867

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) as a staple food, provides a major source of dietary selenium (Se) for humans, which essentially requires Se, however, the molecular mechanism for Se uptake is still poorly understood. Herein, we show evidence that the uptake of selenite, a main bioavailable form of Se in paddy soils, is mediated by a silicon (Si) influx transporter Lsi1 (OsNIP2;1) in rice. Defect of OsNIP2;1 resulted in a significant decrease in the Se concentration of the shoots and xylem sap when selenite was given. However, there was no difference in the Se concentration between the wild-type rice and mutant of OsNIP2;1 when selenate was supplied. A short-term uptake experiment showed that selenite uptake greatly increased with decreasing pH in the external solution. Si as silicic acid did not inhibit the Se uptake from selenite in both rice and yeast (Saccharomyces cerevisiae) at low pHs. Expression of OsNIP2;1 in yeast enhanced the selenite uptake at pH 3.5 and 5.5 but not at pH 7.5. On the other hand, defect of Si efflux transporter Lsi2 did not affect the uptake of Se either from selenite or selenate. Taken together, our results indicate that Si influx transporter OsNIP2;1 is permeable to selenite.

DOI： 10.1104/pp.110.157867

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

ATP-binding cassette (ABC) transporters represent a large family in plants, but the functions of most of these transporters are unknown. Here we report a gene, AtSTAR1, only encoding an ATP-binding domain of a bacterial-type ABC transporter in Arabidopsis (Arabidopsis thaliana). AtSTAR1 is an ortholog of rice (Oryza sativa) OsSTAR1, which has been implicated in aluminum (Al) tolerance. Knockout of AtSTAR1 resulted in increased sensitivity to Al and earlier flowering. Unlike OsSTAR1, AtSTAR1 was expressed in both the roots and shoots and its expression was not induced by Al or other stresses. Investigation of tissue-specific localization of AtSTAR1 through beta-glucuronidase fusion revealed that AtSTAR1 was predominantly expressed at outer cell layers of root tips and developing leaves, whose localization is also different from those of OsSTAR1. However, introduction of OsSTAR1 into atstar1 mutant rescued the sensitivity of atstar1 to Al, indicating that AtSTAR1 has a similar function as OsSTAR1. Furthermore, we found that AtSTAR1 may interact with ALS3, a transmembrane-binding domain in Arabidopsis to form a complex because introduction of OsSTAR1, a functional substitute of AtSTAR1, into als3 mutant resulted in the loss of OsSTAR1 protein. All these findings indicate that AtSTAR1 is involved in the basic detoxification of Al in Arabidopsis.

DOI： 10.1104/pp.110.155028

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記述言語：英語   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

DOI： 10.1111/j.1365-313X.2009.04036.x

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記述言語：英語   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

DOI： 10.1111/j.1365-313X.2009.04036.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice (Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated.
Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally.
Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 mu M arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60-90% of the arsenate uptake. A rice mutant defective in Lsi1 (lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium.
We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15-20% of the total efflux, suggesting the existence of other efflux transporters.

DOI： 10.1111/j.1469-8137.2010.03192.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice (Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated.
Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally.
Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 mu M arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60-90% of the arsenate uptake. A rice mutant defective in Lsi1 (lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium.
We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15-20% of the total efflux, suggesting the existence of other efflux transporters.

DOI： 10.1111/j.1469-8137.2010.03192.x

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Kengo Yokosho, Naoki Yamaji, Jian Feng Ma, 2010, 'Isolation and characterisation of two MATE genes in rye', <i>Functional Plant Biology</i>, vol. 37, no. 4, p. 296

DOI： 10.1071/FP09265

DOI： 10.1071/fp09265

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice (Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated.
Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally.
Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 mu M arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60-90% of the arsenate uptake. A rice mutant defective in Lsi1 (lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium.
We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15-20% of the total efflux, suggesting the existence of other efflux transporters.

DOI： 10.1111/j.1469-8137.2010.03192.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CSIRO PUBLISHING  

Multidrug and toxic compound extrusion (MATE) proteins are widely present in bacteria, fungi, plants and mammals. Recent studies have showed that a group of plant MATE genes encodes citrate transporter, which are involved in the detoxification of aluminium or translocation of iron from the roots to the shoots. In this study, we isolated two homologous genes (ScFRDL1 and ScFRDL2) from this family in rye (Secale cereale L.). ScFRDL1 shared 94.2% identity with HvAACT1, an Al-activated citrate transporter in barley (Hordeum vulgare L.) and ScFRDL2 shared 80.6% identity with OsFRDL2, a putative Al-responsive protein in rice (Oryza sativa L.). Both genes were mainly expressed in the roots, however, they showed different expression patterns. Expression of ScFRDL1 was unaffected by Al treatment, but up-regulated by Fe-deficiency treatment. In contrast, expression of ScFRDL2 was greatly induced by Al but not by Fe deficiency. The Al-induced up-regulation of ScFRDL2 was found in both the root tips and basal roots. Furthermore, the expression pattern of ScFRDL2 was consistent with citrate secretion pattern. Immunostaining showed that ScFRDL1 was localised at all cells in the root tips and central cylinder and endodermis in the basal root. Taken together, our results suggest that ScFRDL1 was involved in efflux of citrate into the xylem for Fe translocation from the roots to the shoots, while ScFRDL2 was involved in Al-activated citrate secretion in rye.

DOI： 10.1071/FP09265

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CSIRO PUBLISHING  

Multidrug and toxic compound extrusion (MATE) proteins are widely present in bacteria, fungi, plants and mammals. Recent studies have showed that a group of plant MATE genes encodes citrate transporter, which are involved in the detoxification of aluminium or translocation of iron from the roots to the shoots. In this study, we isolated two homologous genes (ScFRDL1 and ScFRDL2) from this family in rye (Secale cereale L.). ScFRDL1 shared 94.2% identity with HvAACT1, an Al-activated citrate transporter in barley (Hordeum vulgare L.) and ScFRDL2 shared 80.6% identity with OsFRDL2, a putative Al-responsive protein in rice (Oryza sativa L.). Both genes were mainly expressed in the roots, however, they showed different expression patterns. Expression of ScFRDL1 was unaffected by Al treatment, but up-regulated by Fe-deficiency treatment. In contrast, expression of ScFRDL2 was greatly induced by Al but not by Fe deficiency. The Al-induced up-regulation of ScFRDL2 was found in both the root tips and basal roots. Furthermore, the expression pattern of ScFRDL2 was consistent with citrate secretion pattern. Immunostaining showed that ScFRDL1 was localised at all cells in the root tips and central cylinder and endodermis in the basal root. Taken together, our results suggest that ScFRDL1 was involved in efflux of citrate into the xylem for Fe translocation from the roots to the shoots, while ScFRDL2 was involved in Al-activated citrate secretion in rye.

DOI： 10.1071/FP09265

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Aluminum (Al) toxicity is the major limiting factor of crop production on acid soils, but some plant species have evolved ways of detoxifying Al. Here, we report a C2H2-type zinc finger transcription factor ART1 (for Al resistance transcription factor 1), which specifically regulates the expression of genes related to Al tolerance in rice (Oryza sativa). ART1 is constitutively expressed in the root, and the expression level is not affected by Al treatment. ART1 is localized in the nucleus of all root cells. A yeast one-hybrid assay showed that ART1 has a transcriptional activation potential and interacts with the promoter region of STAR1, an important factor in rice Al tolerance. Microarray analysis revealed 31 downstream transcripts regulated by ART1, including STAR1 and 2 and a couple of homologs of Al tolerance genes in other plants. Some of these genes were implicated in both internal and external detoxification of Al at different cellular levels. Our findings shed light on comprehensively understanding how plants detoxify aluminum to survive in an acidic environment.

DOI： 10.1105/tpc.109.070771

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

The concentration of essential mineral nutrients in the edible portion of plants such as grains may affect the nutritional value of these foods, while concentrations of toxic minerals in the plant are matter of food safety. Minerals taken up by the roots from soils are normally redirected at plant nodes before they are finally transported into developing seeds. However, the molecular mechanisms involved in this process have not been identified so far. Herein, we report on a transporter (Lsi6) responsible for the redirection of a plant nutrient at the node. Lsi6 is a silicon transporter in rice (Oryza sativa), and its expression in node I below the panicles is greatly enhanced when the panicle is completely emerged. Lsi6 is mainly localized at the xylem transfer cells located at the outer boundary region of the enlarged large vascular bundles in node I. Knockout of Lsi6 decreased Si accumulation in the panicles but increased Si accumulation in the flag leaf. These results suggest that Lsi6 is a transporter involved in intervascular transfer (i.e., transfer of silicon from the large vascular bundles coming from the roots to the diffuse vascular bundles connected to the panicles). These findings will be useful for selectively enhancing the accumulation of essential nutrients and reducing toxic minerals in the edible portion of cereals.

DOI： 10.1105/tpc.109.069831

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Roots of some gramineous plants secrete phytosiderophores in response to iron deficiency and take up Fe as a ferric-phytosiderophore complex through the transporter YS1 (Yellow Stripe 1). Here, this transporter in maize (ZmYS1) and barley (HvYS1) was further characterized and compared in terms of expression pattern, diurnal change, and tissue-type specificity of localization. The expression of HvYS1 was specifically induced by Fe deficiency only in barley roots, and increased with the progress of Fe deficiency, whereas ZmYS1 was expressed in maize in the leaf blades and sheaths, crown, and seminal roots, but not in the hypocotyl. HvYS1 expression was not induced by any other metal deficiency. Furthermore, in maize leaf blades, the expression was higher in the young leaf blades showing severe chlorosis than in the old leaf blades showing no chlorosis. The expression of HvYS1 showed a distinct diurnal rhythm, reaching a maximum before the onset of phytosiderophore secretion. In contrast, ZmYS1 did not show such a rhythm in expression. Immunostaining showed that ZmYS1 was localized in the epidermal cells of both crown and lateral roots, with a polar localization at the distal side of the epidermal cells. In maize leaves, ZmYS1 was localized in mesophyll cells, but not epidermal cells. These differences in gene expression pattern and tissue-type specificity of localization suggest that HvYS1 is only involved in primary Fe acquisition by barley roots, whereas ZmYS1 is involved in both primary Fe acquisition and intracellular transport of iron and other metals in maize.

DOI： 10.1093/jxb/erp191

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Silicon (Si) uptake has been extensively examined in rice (Oryza sativa), but it is poorly understood in other gramineous crops. We identified Low Silicon Rice 2 (Lsi2)-like Si efflux transporters from two important gramineous crops: maize (Zea mays) and barley (Hordeum vulgare). Both maize and barley Lsi2 expressed in Xenopus laevis oocytes showed Si efflux transport activity. Furthermore, barley Lsi2 was able to recover Si uptake in a rice mutant defective in Si efflux. Maize and barley Lsi2 were only expressed in the roots. Expression of maize and barley Lsi2 was downregulated in response to exogenously applied Si. Moreover, there was a significant positive correlation between the ability of roots to absorb Si and the expression levels of Lsi2 in eight barley cultivars, suggesting that Lsi2 is a key Si transporter in barley. Immunostaining showed that maize and barley Lsi2 localized only at the endodermis, with no polarity. Protein gel blot analysis indicated that maize and barley Lsi2 localized on the plasma membrane. The unique features of maize and barley Si influx and efflux transporters, including their cell-type specificity and the lack of polarity of their localization in Lsi2, indicate that these crops have a different Si uptake system from that in rice.

DOI： 10.1105/tpc.109.067884

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Outer cell layers of rice roots, which comprise epidermis, exodermis and sclerenchyma, have been proposed to protect the roots from various stresses in soil. Here, we report a mutant which is defective in the specification of outer cell layers, and examined the role of these layers in Al and other metal resistance. Morphological and histochemical observations revealed that the mutant isolated based on Al sensitivity frequently showed a disordered pattern of periclinal cell division in the epidermal layers at a region close to the root apical meristem. The lateral root caps in the mutant became difficult to peel off from the epidermis, and epidermal cells became smaller and irregular with far fewer root hairs. Furthermore, some exodermal cells were transformed into additional sclerenchyma cells. However, there was no difference in the inner cell layers between the wild-type rice and the mutant. The mutant showed similar root growth to the wild-type rice in the absence of Al, but greater inhibition of root elongation by Al was found in the mutant. Morin staining showed that Al penetrated into the inner cortical cells in the mutant. Furthermore, the mutant was also sensitive to other metals including Cd and La. Taken together, our results indicate that root outer cell layers protect the roots against the toxicity of Al and other metals by preventing metal penetration into the inner cells. Genetic analysis showed that the mutant phenotypes were controlled by a single recessive gene, which was located on the short arm of rice chromosome 2.

DOI： 10.1093/pcp/pcp050

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

Most plants accumulate silicon in their bodies, and this is thought to be important for resistance against biotic and abiotic stresses; however, the molecular mechanisms for Si uptake and accumulation are poorly understood. Here, we describe an Si influx transporter, HvLsi1, in barley. This protein is homologous to rice influx transporter OsLsi1 with 81% identity, and belongs to a Nod26-like major intrinsic protein sub-family of aquaporins. Heterologous expression in both Xenopus laevis oocytes and a rice mutant defective in Si uptake showed that HvLsi1 has transport activity for silicic acid. Expression of HvLsi1 was detected specifically in the basal root, and the expression level was not affected by Si supply. There was a weak correlation between Si uptake and the expression level of HvLsi1 in eight cultivars tested. In the seminal roots, HvLsi1 is localized on the plasma membrane on the distal side of epidermal and cortical cells. HvLsi1 is also located in lateral roots on the plasma membrane of hypodermal cells. These cell-type specificity of localization and expression patterns of HvLsi1 are different from those of OsLsi1. These observations indicate that HvLsi1 is a silicon influx transporter that is involved in radial transport of Si through the epidermal and cortical layers of the basal roots of barley.

DOI： 10.1111/j.1365-313X.2008.03728.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL PUBLISHING, INC  

Most plants accumulate silicon in their bodies, and this is thought to be important for resistance against biotic and abiotic stresses; however, the molecular mechanisms for Si uptake and accumulation are poorly understood. Here, we describe an Si influx transporter, HvLsi1, in barley. This protein is homologous to rice influx transporter OsLsi1 with 81% identity, and belongs to a Nod26-like major intrinsic protein sub-family of aquaporins. Heterologous expression in both Xenopus laevis oocytes and a rice mutant defective in Si uptake showed that HvLsi1 has transport activity for silicic acid. Expression of HvLsi1 was detected specifically in the basal root, and the expression level was not affected by Si supply. There was a weak correlation between Si uptake and the expression level of HvLsi1 in eight cultivars tested. In the seminal roots, HvLsi1 is localized on the plasma membrane on the distal side of epidermal and cortical cells. HvLsi1 is also located in lateral roots on the plasma membrane of hypodermal cells. These cell-type specificity of localization and expression patterns of HvLsi1 are different from those of OsLsi1. These observations indicate that HvLsi1 is a silicon influx transporter that is involved in radial transport of Si through the epidermal and cortical layers of the basal roots of barley.

DOI： 10.1111/j.1365-313X.2008.03728.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Aluminum (Al) toxicity is a major factor limiting crop production in acidic soil, but the molecular mechanisms of Al tolerance are poorly understood. Here, we report that two genes, STAR1 (for sensitive to Al rhizotoxicity1) and STAR2, are responsible for Al tolerance in rice. STAR1 encodes a nucleotide binding domain, while STAR2 encodes a transmembrane domain, of a bacterial-type ATP binding cassette (ABC) transporter. Disruption of either gene resulted in hypersensitivity to aluminum toxicity. Both STAR1 and STAR2 are expressed mainly in the roots and are specifically induced by Al exposure. Expression in onion epidermal cells, rice protoplasts, and yeast showed that STAR1 interacts with STAR2 to form a complex that localizes to the vesicle membranes of all root cells, except for those in the epidermal layer of the mature zone. When expressed together in Xenopus laevis oocytes, STAR1/2 shows efflux transport activity specific for UDP-glucose. Furthermore, addition of exogenous UDP-glucose rescued root growth in the star1 mutant exposed to Al. These results indicate that STAR1 and STAR2 form a complex that functions as an ABC transporter, which is required for detoxification of Al in rice. The ABC transporter transports UDP-glucose, which may be used to modify the cell wall.

DOI： 10.1105/tpc.108.064543

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Multidrug and toxic compound extrusion (MATE) transporters represent a large family in plants, but their functions are poorly understood. Here, we report the function of a rice (Oryza sativa) MATE gene (Os03g0216700, OsFRDL1), the closest homolog of barley (Hordeum vulgare) HvAACT1 (aluminum [Al]-activated citrate transporter 1), in terms of metal stress (iron [Fe] deficiency and Al toxicity). This gene was mainly expressed in the roots and the expression level was not affected by either Fe deficiency or Al toxicity. Knockout of this gene resulted in leaf chlorosis, lower leaf Fe concentration, higher accumulation of zinc and manganese concentration in the leaves, and precipitation of Fe in the root's stele. The concentration of citrate and ferric iron in the xylem sap was lower in the knockout line compared to the wild-type rice. Heterologous expression of OsFRDL1 in Xenopus oocytes showed transport activity for citrate. Immunostaining showed that OsFRDL1 was localized at the pericycle cells of the roots. On the other hand, there was no difference in the Al-induced secretion of citrate from the roots between the knockout line and the wild-type rice. Taken together, our results indicate that OsFRDL1 is a citrate transporter localized at the pericycle cells, which is necessary for efficient translocation of Fe to the shoot as a Fe-citrate complex.

DOI： 10.1104/pp.108.128132

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Maize (Zea mays L.) shows a high accumulation of silicon (Si), but transporters involved in the uptake and distribution have not been identified. In the present study, we isolated two genes (ZmLsi1 and ZmLsi6), which are homologous to rice influx Si transporter OsLsi1. Heterologous expression in Xenopus laevis oocytes showed that both ZmLsi1 and ZmLsi6 are permeable to silicic acid. ZmLsi1 was mainly expressed in the roots. By contrast, ZmLsi6 was expressed more in the leaf sheaths and blades. Different from OsLsi1, the expression level of both ZmLsi1 and ZmLsi6 was unaffected by Si supply. Immunostaining showed that ZmLsi1 was localized on the plasma membrane of the distal side of root epidermal and hypodermal cells in the seminal and crown roots, and also in cortex cells in lateral roots. In the shoots, ZmLsi6 was found in the xylem parenchyma cells that are adjacent to the vessels in both leaf sheaths and leaf blades. ZmLsi6 in the leaf sheaths and blades also exhibited polar localization on the side facing towards the vessel. Taken together, it can be concluded that ZmLsi1 is an influx transporter of Si, which is responsible for the transport of Si from the external solution to the root cells and that ZmLsi6 mainly functions as a Si transporter for xylem unloading.

DOI： 10.1093/pcp/pcn110

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：INT UNION PURE APPLIED CHEMISTRY  

Iron (Fe) is an essential element for plant growth. Gramineous plants have generally developed a distinct strategy to efficiently acquire insoluble Fe, which is characterized by the synthesis and secretion of an Fe-chelating substance, phytosiderophore (PS) such as mugineic acid (MA), and by a specific uptake system for Fe(III)-PS complexes. In a previous study, we identified a gene specifically encoding an Fe(III)-PS transporter (HvYS1) in barley. This gene as well as the encoded protein is specifically expressed in the epidermal cells of the roots, and gene expression is greatly enhanced under Fe-deficient conditions. The localization and substrate specificity of HvYS1 indicate that it is a Fe(III)-PS specific transporter in barley roots. In contrast, ZmYS1, which has been reported as ail Fe-PS transporter from maize, possesses broad substrate specificity despite a high homology with HvYS1. By assessing the transport activity of a series of HvYS1-ZmYS1 chimeras, we revealed that the outer membrane loop between the 6(th) and 7(th) transmembrane regions is essential for the substrate specificity. We also achieved an efficient short-step synthesis of MA and 2'-deoxymugineic acid (DMA). Our new synthetic method enabled us to use them in a large quantity for biological studies.

DOI： 10.1351/pac200880122689

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記述言語：英語   出版者・発行元：BIRKHAUSER VERLAG AG  

Silicon exerts beneficial effects on plant growth and production by alleviating both biotic and abiotic stresses including diseases, pests, lodging, drought, and nutrient imbalance. Recently, two genes (Lsi1 and Lsi2) encoding Si transporters have been identified from rice. Lsi1 (low silicon 1) belongs to a Nod26-like major intrinsic protein subfamily in aquaporin, while Lsi2 encodes a putative anion transporter. Lsi1 is localized on the distal side of both exodermis and endodermis in rice roots, while Lsi2 is localized on the proximal side of the same cells. Lsi1 shows influx transport activity for Si, while Lsi2 shows efflux transport activity. Therefore, Lsi1 is responsible for transport of Si from the external solution to the root cells, whereas Lsi2 is an efflux transporter responsible for the transport of Si from the root cells to the apoplast. Coupling of Lsi1 with Lsi2 is required for efficient uptake of Si in rice.

DOI： 10.1007/s00018-008-7580-x

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記述言語：英語   出版者・発行元：SPRINGER  

Lsi1 (OsNIP2;1) is the first silicon (silicic acid) transporter identified in plant, which belongs to the nodulin 26-like intrinsic membrane protein (NIP) subfamily. In this study, we characterized the function of this transporter by using the Xenopus laevis oocyte expression system. The transport activity of Lsi1 for silicic acid was significantly inhibited by HgCl(2) but not by low temperature. Lsi1 also showed an efflux transport activity for silicic acid. The substrate specificity study showed that Lsi1 was able to transport urea and boric acid; however, the transport activity for silicic acid was not affected by the presence of equimolar urea and was decreased only slightly by boric acid. Furthermore, among the NIPs subgroup, OsNIP2;2 showed transport activity for silicic acid, whereas OsNIP1;1 and OsNIP3;1 did not. We propose that Lsi1 and its close homologues form a unique subgroup of NIP with a distinct ar/R selectivity filter, which is located in the narrowest region on the extra-membrane mouth and govern the substrate specificity of the pore.

DOI： 10.1007/s00424-007-0408-y

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Arsenic poisoning affects millions of people worldwide. Human arsenic intake from rice consumption can be substantial because rice is particularly efficient in assimilating arsenic from paddy soils, although the mechanism has not been elucidated. Here we report that two different types of transporters mediate transport of arsenite, the predominant form of arsenic in paddy soil, from the external medium to the xylem. Transporters belonging to the NIP subfamily of aquaporins in rice are permeable to arsenite but not to arsenate. Mutation in OsNIP2;1 (Lsi1, a silicon influx transporter) significantly decreases arsenite uptake. Furthermore, in the rice mutants defective in the silicon efflux transporter Lsi2, arsenite transport to the xylem and accumulation in shoots and grain decreased greatly. Mutation in Lsi2 had a much greater impact on arsenic accumulation in shoots and grain in field-grown rice than Lsi1. Arsenite transport in rice roots therefore shares the same highly efficient pathway as silicon, which explains why rice is efficient in arsenic accumulation. Our results provide insight into the uptake mechanism of arsenite in rice and strategies for reducing arsenic accumulation in grain for enhanced food safety.

DOI： 10.1073/pnas.0802361105

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記述言語：英語   出版者・発行元：SPRINGER  

Lsi1 (OsNIP2;1) is the first silicon (silicic acid) transporter identified in plant, which belongs to the nodulin 26-like intrinsic membrane protein (NIP) subfamily. In this study, we characterized the function of this transporter by using the Xenopus laevis oocyte expression system. The transport activity of Lsi1 for silicic acid was significantly inhibited by HgCl(2) but not by low temperature. Lsi1 also showed an efflux transport activity for silicic acid. The substrate specificity study showed that Lsi1 was able to transport urea and boric acid; however, the transport activity for silicic acid was not affected by the presence of equimolar urea and was decreased only slightly by boric acid. Furthermore, among the NIPs subgroup, OsNIP2;2 showed transport activity for silicic acid, whereas OsNIP1;1 and OsNIP3;1 did not. We propose that Lsi1 and its close homologues form a unique subgroup of NIP with a distinct ar/R selectivity filter, which is located in the narrowest region on the extra-membrane mouth and govern the substrate specificity of the pore.

DOI： 10.1007/s00424-007-0408-y

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) accumulates very high concentrations of silicon (Si) in the shoots, and the deposition of Si as amorphous silica helps plants to overcome biotic and abiotic stresses. Here, we describe a transporter, Lsi6, which is involved in the distribution of Si in the shoots. Lsi6 belongs to the nodulin-26 intrinsic protein III subgroup of aquaporins and is permeable to silicic acid. Lsi6 is expressed in the leaf sheath and leaf blades as well as in the root tips. Cellular localization studies revealed that Lsi6 is found in the xylem parenchyma cells of the leaf sheath and leaf blades. Moreover, Lsi6 showed polar localization at the side facing toward the vessel. Knockdown of Lsi6 did not affect the uptake of Si by the roots but resulted in disordered deposition of silica in the shoots and increased excretion of Si in the guttation fluid. These results indicate that Lsi6 is a transporter responsible for the transport of Si out of the xylem and subsequently affects the distribution of Si in the leaf.

DOI： 10.1105/tpc.108.059311

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) is a highly silicon (Si)-accumulating species that shows genotypic differences in Si accumulation. We investigated the physiological and molecular mechanisms involved in the genotypic difference in Si uptake between the japonica var. Nipponbare and the indica var. Kasalath. Both the Si concentration in the shoot and the Si uptake per root dry weight were higher in Nipponbare than in Kasalath grown in either soil or nutrient solution. The Si uptake by a single root was also higher in Nipponbare than in Kasalath. A kinetics study showed that Nipponbare and Kasalath had a similar K-m value, whereas the V-max was higher in Nipponbare. The expression of two Si transporter genes (Low silicon rice 1 [Lsi1] and Lsi2) investigated using real-time reverse transcription polymerase chain reaction revealed higher expression of both genes in Nipponbare than in Kasalath. Immunostaining with Lsi1 and Lsi2 antibodies revealed a similar pattern of subcellular localization of these two Si transporters in both varieties; Lsi1 and Lsi2 were localized at the distal and proximal sides, respectively, of both exodermis and endodermis of the roots. These results revealed that the genotypic difference in the Si accumulation results from the difference in abundance of Si transporters in rice roots.

DOI： 10.1104/pp.107.107599

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We examined the effect of ectopic expression of WUS on the morphology of tobacco seedlings and the segments in vitro. WUS was amplified from Arabidopsis cDNA and introduced into the tobacco genome under the transcriptional control of the beta-estradiol-inducible expression system. When 1-week-old transgenic seedlings were cultured in the presence of beta-estradiol, only the root tip region developed bulbous tissues followed by shoot formation and plant regeneration, suggesting its applicability for improving the strategy of micropropagation in recalcitrant species. Evident abnormality was not observed in the cotyledons, hypocotyl nor root except for the tip. However, ectopic WUS seemed to be functional in those parts through the observation of gene expression and the behavior of cultured segments. Small root segments with a root tip treated with beta-estradiol also showed bulbing but no shoots unless exogenous cytokinin was supplied. These findings suggest the existence of unknown factors regulating ectopic WUS function in the seedling.

DOI： 10.1007/s00299-007-0342-7

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Silicon is an important nutrient for the optimal growth and sustainable production of rice(1-4). Rice accumulates up to 10% silicon in the shoot, and this high accumulation is required to protect the plant from multiple abiotic and biotic stresses(1-5). A gene, Lsi1, that encodes a silicon influx transporter has been identified in rice(6). Here we describe a previously uncharacterized gene, low silicon rice 2 (Lsi2), which has no similarity to Lsi1. This gene is constitutively expressed in the roots. The protein encoded by this gene is localized, like Lsi1, on the plasma membrane of cells in both the exodermis and the endodermis, but in contrast to Lsi1, which is localized on the distal side, Lsi2 is localized on the proximal side of the same cells. Expression of Lsi2 in Xenopus oocytes did not result in influx transport activity for silicon, but preloading of the oocytes with silicon resulted in a release of silicon, indicating that Lsi2 is a silicon efflux transporter. The identification of this silicon transporter revealed a unique mechanism of nutrient transport in plants: having an influx transporter on one side and an efflux transporter on the other side of the cell to permit the effective transcellular transport of the nutrients.

DOI： 10.1038/nature05964

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Background and Aims Ethylene diamine tetraacetic acid (EDTA)-assisted phytoremediation has been developed to clean up lead (Pb)-contaminated soil; however, the mechanism responsible for the uptake of EDTA-Pb complex is not well understood. In this study, the accumulation process of Pb from EDTA-Pb is characterized in comparison to ionic Pb [Pb(NO3)(2)] in sorghum (Sorghum bicolor).
Methods Sorghum seedlings were exposed to a 0.5 mm CaCl2 (pH 5.0) solution containing 0, 1 mm Pb(NO3)(2) or EDTA-Pb complexes at a molar ratio of 1:0.5, 1:1, 1:2 and 1:4 (Pb:EDTA). The root elongation of sorghum at different ratios of Pb:EDTA was measured. Xylem sap was collected after the stem was severed at different times. The concentration of Pb in the shoots and roots were determined by an atomic absorption spectrometer. In addition, the roots were stained with Fluostain I for observation of the root structure.
Key Results Lead accumulation in the shoots of the plants exposed to EDTA-Pb at 1:1 ratio was only one-fifth of that exposed to ionic Pb at the same concentration. Lead accumulation decreased when transpiration was suppressed. The concentration of Pb in the xylem sap from the EDTA-Pb-treated plants was about 1/25 000 of that in the external solution. Root elongation was severely inhibited by ionic Pb, but not by EDTA-Pb at a 1:1 ratio. Root staining showed that a physiological barrier was damaged in the roots exposed to ionic Pb, but not in the roots exposed to EDTA-Pb.
Conclusions All these results suggest that sorghum roots are inefficient in uptake of EDTA-chelated Pb and that enhanced Pb accumulation from ionic Pb was attributed to the damaged structure of the roots.

DOI： 10.1093/aob/mcm038

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC PLANT BIOLOGISTS  

Rice (Oryza sativa) is a typical silicon (Si) accumulator and requires a large amount of Si for high-yield production. Recently, a gene (Low silicon rice1 [Lsi1]) encoding a Si transporter was identified in rice roots. Here, we characterized Lsi1 in terms of spatial distribution and temporal variation using both physiological and molecular approaches. Results from a multicompartment transport box experiment showed that the major site for Si uptake was located at the basal zone (> 10 mm from the root tip) of the roots rather than at the root tips (< 10 mm from the root tip). Consistent with the Si uptake pattern, Lsi1 expression and distribution of the Lsi1 protein were found only in the basal zone of roots. In the basal zones of the seminal, crown, and lateral roots, the Lsi1 protein showed a polar localization at the distal side of both the exodermis and endodermis, where the Casparian bands are formed. This indicates that Lsi1 is required for the transport of Si through the cells of the exodermis and endodermis. Expression of Lsi1 displayed a distinct diurnal pattern. Furthermore, expression was transiently enhanced around the heading stage, which coincides with a high Si requirement during this growth stage. Expression was down-regulated by dehydration stress and abscisic acid, suggesting that expression of Lsi1 may be regulated by abscisic acid.

DOI： 10.1104/pp.106.093005

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DOI： 10.14841/jspp.2007.0.113.0

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DOI： 10.14841/jspp.2007.0.054.0

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

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DOI： 10.1093/pcp/pcm091

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE LONDON  

Silicon (Si) accumulation differs greatly between plant species because of differences in Si uptake by the roots. Recently, a gene encoding a Si uptake transporter in rice, a typical Si-accumulating plant, was isolated. The beneficial effects of Si are mainly associated with its high deposition in plant tissues, enhancing their strength and rigidity. However, Si might play an active role in enhancing host resistance to plant diseases by stimulating defense reaction mechanisms. Because many plants are not able to accumulate Si at high enough levels to be beneficial, genetically manipulating the Si uptake capacity of the root might help plants to accumulate more Si and, hence, improve their ability to overcome biotic and abiotic stresses.

DOI： 10.1016/j.tplants.2006.06.007

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE LONDON  

Silicon (Si) accumulation differs greatly between plant species because of differences in Si uptake by the roots. Recently, a gene encoding a Si uptake transporter in rice, a typical Si-accumulating plant, was isolated. The beneficial effects of Si are mainly associated with its high deposition in plant tissues, enhancing their strength and rigidity. However, Si might play an active role in enhancing host resistance to plant diseases by stimulating defense reaction mechanisms. Because many plants are not able to accumulate Si at high enough levels to be beneficial, genetically manipulating the Si uptake capacity of the root might help plants to accumulate more Si and, hence, improve their ability to overcome biotic and abiotic stresses.

DOI： 10.1016/j.tplants.2006.06.007

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

In order to visualize the specific state of tobacco pollen undergoing dedifferentiation from immature pollen to embryogenic cells, we established tobacco marker lines transgenic for a vital reporter gene regulated under the transcriptional control of an 840 bp fragment, named A22pro. This fragment was obtained from the 5'-flanking region of a gene corresponding to a cDNA named A22 that was previously isolated through differential screening from a cDNA library prepared from tobacco pollen undergoing dedifferentiation. The reporter gene, named H3sGFP, consisting of synthetic green fluorescent protein gene (sGFP) and tobacco H3 histone gene for nuclear localization, was designed to distinguish the gene expression in the generative cell from that in the vegetative cell in a pollen grain. The marker line produced pollen showing a green fluorescent signal in the generative nuclei (GN) but the expression level of the transgene was low. Pollen after culture for dedifferentiation showed an intense signal transiently in the vegetative nuclei (VN), at a specific developmental stage of pollen, with a rapid increase of expression level of the transgene. Serial observations revealed that all androgenic embryos originated from the pollen grains that had shown the signal in their VN. Thus, A22pro is originally functional in gametogenesis but is activated in VN of pollen undergoing embryogenic dedifferentiation. Additionally, we observed a gene expression pattern identical to that described above, using another 5'-flanking region of a gene for a cDNA, named B27pro, homologous to A22 as a promoter of the reporter gene.

DOI： 10.1007/s00299-005-0076-3

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：BLACKWELL PUBLISHING  

Iron acquisition of graminaceous plants is characterized by the synthesis and secretion of the iron-chelating phytosiderophore, mugineic acid (MA), and by a specific uptake system for iron(III)-phytosiderophore complexes. We identified a gene specifically encoding an iron-phytosiderophore transporter (HvYS1) in barley, which is the most tolerant species to iron deficiency among graminaceous plants. HvYS1 was predicted to encode a polypeptide of 678 amino acids and to have 72.7% identity with ZmYS1, a first protein identified as an iron(III)-phytosiderophore transporter in maize. Real-time RT-PCR analysis showed that the HvYS1 gene was mainly expressed in the roots, and its expression was enhanced under iron deficiency. In situ hybridization analysis of iron-deficient barley roots revealed that the mRNA of HvYS1 was localized in epidermal root cells. Furthermore, immunohistological staining with anti-HvYS1 polyclonal antibody showed the same localization as the mRNA. HvYS1 functionally complemented yeast strains defective in iron uptake on media containing iron(III)-MA, but not iron-nicotianamine (NA). Expression of HvYS1 in Xenopus oocytes showed strict specificity for both metals and ligands: HvYS1 transports only iron(III) chelated with phytosiderophore. The localization and substrate specificity of HvYS1 is different from those of ZmYS1, indicating that HvYS1 is a specific transporter for iron(III)-phytosiderophore involved in primary iron acquisition from soil in barley roots.

DOI： 10.1111/j.1365-313X.2006.02714.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：BLACKWELL PUBLISHING  

Iron acquisition of graminaceous plants is characterized by the synthesis and secretion of the iron-chelating phytosiderophore, mugineic acid (MA), and by a specific uptake system for iron(III)-phytosiderophore complexes. We identified a gene specifically encoding an iron-phytosiderophore transporter (HvYS1) in barley, which is the most tolerant species to iron deficiency among graminaceous plants. HvYS1 was predicted to encode a polypeptide of 678 amino acids and to have 72.7% identity with ZmYS1, a first protein identified as an iron(III)-phytosiderophore transporter in maize. Real-time RT-PCR analysis showed that the HvYS1 gene was mainly expressed in the roots, and its expression was enhanced under iron deficiency. In situ hybridization analysis of iron-deficient barley roots revealed that the mRNA of HvYS1 was localized in epidermal root cells. Furthermore, immunohistological staining with anti-HvYS1 polyclonal antibody showed the same localization as the mRNA. HvYS1 functionally complemented yeast strains defective in iron uptake on media containing iron(III)-MA, but not iron-nicotianamine (NA). Expression of HvYS1 in Xenopus oocytes showed strict specificity for both metals and ligands: HvYS1 transports only iron(III) chelated with phytosiderophore. The localization and substrate specificity of HvYS1 is different from those of ZmYS1, indicating that HvYS1 is a specific transporter for iron(III)-phytosiderophore involved in primary iron acquisition from soil in barley roots.

DOI： 10.1111/j.1365-313X.2006.02714.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging ( falling over) and increasing resistance to pests and diseases, as well as other stresses(1-3). Silicon is essential for high and sustainable production of rice(4), but the molecular mechanism responsible for the uptake of silicon is unknown. Here we describe the Low silicon rice 1 (Lsi1) gene, which controls silicon accumulation in rice, a typical silicon-accumulating plant. This gene belongs to the aquaporin family(5) and is constitutively expressed in the roots. Lsi1 is localized on the plasma membrane of the distal side of both exodermis and endodermis cells, where casparian strips are located. Suppression of Lsi1 expression resulted in reduced silicon uptake. Furthermore, expression of Lsi1 in Xenopus oocytes showed transport activity for silicon only. The identification of a silicon transporter provides both an insight into the silicon uptake system in plants, and a new strategy for producing crops with high resistance to multiple stresses by genetic modification of the root's silicon uptake capacity.

DOI： 10.1038/nature04590

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DOI： 10.14841/jspp.2006.0.149.0

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI IRELAND LTD  

We conducted differential screening to obtain cDNAs showing that gene expression is highly associated with the transformation from immature pollen to embryogenic cell, so-called embryogenic dedifferentiation of pollen, in a Nicotiana tabacum pollen culture system and analyzed their expression and sequences. Seventy-seven cDNA clones were independently isolated and distinguished into 16 groups based on their sequences. The groups were further categorized into two classes, Class I and II, based on the gene expression pattern of the representative clone of each group under various pollen culture conditions arranged for examining the coincidence with the dedifferentiation. The 13 groups in Class I showed prominent expression under the conditions allowing or facilitating pollen dedifferentiation and the expression level increased earlier than A-type cyclin genes, but they were not markedly expressed in the cell populations rich in S-phase cells, i.e. young anthers with pollen mother cells, BY-2 cells at the growth phase and early phase embryos derived from immature pollen. The other three groups in Class II encoded homologs to H1 histone, H2A histone and minichromosome maintenance (MCM) protein, respectively. The level of their transcripts increased during dedifferentiation. but it was also high in anthers containing pollen mother cells and in the proliferating BY-2 cells indicating that their expression is coincident with the S phase but not with dedifferentiation. These findings suggest that pollen dedifferentiation is a complex process accompanied with the reentrance of cell cycle and unknown events probably caused by specific expression of many genes, at least, listed in Class I. These genes should be used as reliable markers and important clues for further studies on the molecular mechanism of dedifferentiation. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.

DOI： 10.1016/S0168-9452(03)00111-0

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI IRELAND LTD  

Several phosphoproteins, Nicotiana tabacum L. embryogenic pollen-abundant phosphoproteins (NtEPs), characteristically appear in the dedifferentiation process from immature pollen grains to embryogenic cells in a pollen culture system. Among NtEPs we focused our attention on three proteins (NtEPb1-b3) which showed the highest correlation with the dedifferentiation and possessed different pI values and similar molecular weights (ca. 22 kDa). Using probes designed from the N-terminal amino acid sequence common to the three, we isolated 14 clones of cDNA belonging to three similar sequences which probably correspond to NtEPb1-b3. The predicted amino acid sequences showed moderate homology to NtEPc, several type-1 copper-binding glycoproteins and a kind of early nodulin. The level of the transcripts for NtEPbs is highly associated with the pollen dedifferentiation but not with pollen maturation nor with cell division accompanied by meiosis or proliferation of BY-2 cells. Such an expression manner was distinguished from that of a gene coding for A-type cyclin (Ntcyc 25), indicating that NtEPb genes are not under cell cycle control. These results suggest that there exist genes related to an unknown event other than the reentrance of cell cycle in the dedifferentiation process of immature pollen that may be important for acquisition of embryogenic competence. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

DOI： 10.1016/S0168-9452(02)00280-7

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記述言語：日本語  

DOI： 10.20710/dojo.83.3_319

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記述言語：日本語   出版者・発行元：一般社団法人日本土壌肥料学会  

DOI： 10.20710/dojo.81.5_518

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記述言語：日本語   出版者・発行元：一般社団法人日本土壌肥料学会  

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記述言語：日本語   出版者・発行元：植物化学調節学会  

Plants are characterized by mineral nutrition, which require 17 essential elements for their growth. Among them, 14 are minerals. These minerals are taken up by the roots, translocated from the roots to the shoots and finally distributed to different cells for functions. A large number of transporters is required for these transport processes. On the other hand, plants are exposed to toxic minerals, therefore detoxification of these minerals by plants at different cellular levels is also required for survival. Herein, we reviewed recent progresses in identification of transporters involved in uptake, translocation, and distribution of essential minerals and of transporters involved in the detoxification of toxic minerals, focusing on iron (Fe), silicon (Si) and aluminum (Al), which represent essential, beneficial and toxic minerals, respectively.

DOI： 10.18978/jscrp.45.1_49

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記述言語：日本語   出版者・発行元：一般社団法人日本土壌肥料学会  

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記述言語：日本語   出版者・発行元：Japan Society for Bioscience, Biotechnology, and Agrochemistry  

DOI： 10.1271/kagakutoseibutsu1962.44.453

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記述言語：英語   出版者・発行元：The Japan Society of Mechanical Engineers  

In this work, a feasibility study has been conducted to determine if GHTA (Gas Hollow Tungsten Arc) method can be used for the welding in space. As previously described, the test for GHTA welding of stainless steel without filler wire has been successfully performed in a simulated space environment, produced by the parabolic flight of aircraft. In this paper, melt-run welding tests and butt welding tests on stainless steels for GHTA welding with filler wire have been conducted in a vacuum chamber using a developed compact wire feeder. The results are summarized as follows. (1) The developed compact wire feeder makes it possible to add the filler metal to GHTA weld pool smoothly in a vacuum. (2) A metal vapor plume is formed on the molten pool in GHTA welding and it grows brightly with increase of arc current. (3) The penetration depth in GHTA welding becomes shallow with increase of filler metal, as well as that in GTA welding under the atmospheric pressure. (4) The butt joint welded by the GHTA method of filler wire addition has no defect and it has enough strength.

DOI： 10.1299/kikaic.67.2044

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