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Shoot-Silicon-Signal protein to regulate root silicon uptake in rice

Naoki Yamaji, Namiki Mitani-Ueno, Toshiki Fujii, Tomonori Shinya, Ji Feng Shao, Shota Watanuki, Yasunori Saitoh, Jian Feng Ma

Nature Communications 15 ( 1 ) 2024年12月

Comprehensive analysis of silicon impact on defense and metabolic responses in rice exposed to herbivory stress 査読

Dandy Ahamefula Osibe, Yuko Hojo, Tomonori Shinya, Namiki Mitani-Ueno, Ivan Galis

Frontiers in Plant Science 15 2024年5月

掲載種別：研究論文（学術雑誌）出版者・発行元：Frontiers Media SA

Silicon (Si) uptake is generally beneficial for plants that need protection from insect herbivores. In pursue of mechanisms involved in Si-mediated defense, we comprehensively explored the impact of Si on several defensive and metabolic traits in rice exposed to simulated and real herbivory of Mythimna loreyi Duponchel larvae. Hydroponic experiments showed that Si-deprived rice supplemented with Si 72 h prior to insect infestation were similarly resistant to larvae as plants continuously grown in Si-containing media. Both Si and herbivory altered primary metabolism in rice, including the levels of several sugars, amino acids, and organic acids. While the accumulation of sugars was generally positively correlated with Si presence, multiple amino acids showed a negative correlation trend with Si supplementation. The levels of secondary metabolites, including isopentylamine, p-coumaroylputrescine and feruloylputrescine, were typically higher in the leaves of Si-supplemented plants exposed to herbivory stress compared to Si-deprived plants. In addition, simulated herbivory treatment in Si-supplemented plants induced more volatile emissions relative to Si-deprived plants, which was consistent with the increased transcripts of key genes involved in volatile biosynthesis. In ecological interactions, Si alone did not affect the oviposition choice of M. loreyi but gravid females showed a significant preference for simulated herbivory-treated/Si-deprived compared to Si-supplemented plants. Our data suggest that apart from mechanical defense, Si may affect rice metabolism in multiple ways that might enhance/modulate defense responses of rice under herbivory stress.

DOI： 10.3389/fpls.2024.1399562

Knockout of a rice K5.2 gene increases Ca accumulation in the grain. 査読国際誌

Peitong Wang, Naoki Yamaji, Namiki Mitani-Ueno, Jun Ge, Jian Feng Ma

Journal of integrative plant biology 2024年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Rice is a staple food for half world's population, but it is a poor dietary source of calcium (Ca) due to its low concentration. Therefore, it is an important issue to boost the Ca concentration in the grain for improving Ca deficiency risk, but the mechanisms underlying the Ca accumulation are poorly understood. Here, we obtained a rice (Oryza sativa) mutant with high shoot Ca accumulation. The mutant exhibited 26-53% higher Ca in the shoots than that in wild-type rice (WT) at different Ca supplies. The Ca concentration in the xylem sap was 36% higher in the mutant than in the WT. There was no difference in agronomic traits between the WT and mutant, but the mutant showed 25% higher Ca in the polished grain compared with the WT. Map-based cloning combined with complementation test revealed that the mutant phenotype was caused by an 18-bp deletion of a gene, OsK5.2 belonging to Shaker-like K+ channel family. OsK.2 was highly expressed in the mature region of the roots and its expression in the roots was not affected by Ca levels, but up-regulated by low K. Immunostaining showed that OsK.2 was mainly expressed in pericycle of the roots. Taken together, our results revealed a novel role of OsK.2 in Ca translocation in rice, which will be a good target for Ca biofortification in rice. This article is protected by copyright. All rights reserved.

DOI： 10.1111/jipb.13587

A silicon transporter gene required for healthy growth of rice on land. 査読国際誌

Namiki Mitani-Ueno, Naoki Yamaji, Sheng Huang, Yuma Yoshioka, Takaaki Miyaji, Jian Feng Ma

Nature communications 14 ( 1 ) 6522 - 6522 2023年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Silicon (Si) is the most abundant mineral element in the earth's crust. Some plants actively accumulate Si as amorphous silica (phytoliths), which can protect plants from stresses. Here, we report a gene (SIET4) that is required for the proper accumulation and cell-specific deposition of Si in rice and show that it is essential for normal growth. SIET4 is constitutively expressed in leaves and encodes a Si transporter. SlET4 polarly localizes at the distal side of epidermal cells and cells surrounding the bulliform cells (motor cells) of the leaf blade, where Si is deposited. Knockout of SIET4 leads to the death of rice in the presence but not absence of Si. Further analysis shows that SIET4 knockout induces abnormal Si deposition in mesophyll cells and the induction of hundreds of genes related to various stress responses. These results indicate that SIET4 is required for the proper export of Si from leaf cells to the leaf surface and for the healthy growth of rice on land.

DOI： 10.1038/s41467-023-42180-y

Polar localization of a rice silicon transporter requires isoleucine at both C- and N-termini as well as positively charged residues. 査読国際誌

Noriyuki Konishi, Namiki Mitani-Ueno, Naoki Yamaji, Jian Feng Ma

The Plant cell 35 ( 6 ) 2232 - 2250 2023年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Silicon (Si) is important for stable and high yields in rice (Oryza sativa), a typical Si hyperaccumulator. The high Si accumulation is achieved by the cooperation of 2 Si transporters, LOW SILICON 1 (OsLsi1) and OsLsi2, which are polarly localized in cells of the root exodermis and endodermis. However, the mechanism underlying their polar localization is unknown. Here, we identified amino acid residues critical for the polar localization of OsLsi1. Deletion of both N- and C-terminal regions resulted in the loss of its polar localization. Furthermore, the deletion of the C-terminus inhibited its trafficking from the endoplasmic reticulum to the plasma membrane. Detailed site-directed mutagenesis analysis showed that Ile18 at the N-terminal region and Ile285 at the C-terminal region were essential for the polar localization of OsLsi1. Moreover, a cluster of positively charged residues at the C-terminal region is also required for polar localization. Phosphorylation and Lys modifications of OsLsi1 are unlikely to be involved in its polar localization. Finally, we showed that the polar localization of OsLsi1 is required for the efficient uptake of Si. Our study not only identified critical residues required for the polar localization of OsLsi1, but also provided experimental evidence for the importance of transporter polarity for efficient nutrient uptake.

DOI： 10.1093/plcell/koad073

A pericycle‐localized silicon transporter for efficient xylem loading in rice 査読

Sheng Huang, Naoki Yamaji, Gen Sakurai, Namiki Mitani‐Ueno, Noriyuki Konishi, Jian Feng Ma

New Phytologist 234 ( 1 ) 197 - 208 2022年4月

Boron uptake in rice is regulated post-translationally via a clathrin-independent pathway 査読

Sheng Huang, Noriyuki Konishi, Naoki Yamaji, Ji Feng Shao, Namiki Mitani-Ueno, Jian Feng Ma

Plant Physiology 188 ( 3 ) 1649 - 1664 2022年3月

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 (OUP)

Abstract

Uptake of boron (B) in rice (Oryza sativa) is mediated by the Low silicon rice 1 (OsLsi1) channel, belonging to the NOD26-like intrinsic protein III subgroup, and the efflux transporter B transporter 1 (OsBOR1). However, it is unknown how these transporters cooperate for B uptake and how they are regulated in response to B fluctuations. Here, we examined the response of these two transporters to environmental B changes at the transcriptional and posttranslational level. OsBOR1 showed polar localization at the proximal side of both the exodermis and endodermis of mature root region, forming an efficient uptake system with OsLsi1 polarly localized at the distal side of the same cell layers. Expression of OsBOR1 and OsLsi1 was unaffected by B deficiency and excess. However, although OsLsi1 protein did not respond to high B at the protein level, OsBOR1 was degraded in response to high B within hours, which was accompanied with a significant decrease of total B uptake. The high B-induced degradation of OsBOR1 was inhibited in the presence of MG-132, a proteasome inhibitor, without disturbance of the polar localization. In contrast, neither the high B-induced degradation of OsBOR1 nor its polarity was affected by induced expression of dominant-negative mutated dynamin-related protein 1A (OsDRP1AK47A) or knockout of the mu subunit (AP2M) of adaptor protein-2 complex, suggesting that clathrin-mediated endocytosis is not involved in OsBOR1 degradation and polar localization. These results indicate that, in contrast to Arabidopsis thaliana, rice has a distinct regulatory mechanism for B uptake through clathrin-independent degradation of OsBOR1 in response to high B.

DOI： 10.1093/plphys/kiab575

その他リンク： https://academic.oup.com/plphys/article-pdf/188/3/1649/42744142/kiab575.pdf

A crucial role for a node-localized transporter, HvSPDT, in loading phosphorus into barley grains. 査読国際誌

Mian Gu, Hengliang Huang, Hiroshi Hisano, Guangda Ding, Sheng Huang, Namiki Mitani-Ueno, Kengo Yokosho, Kazuhiro Sato, Naoki Yamaji, Jian Feng Ma

New phytologist 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Grains are the major sink of phosphorus (P) in cereal crops, accounting for 60-85% of total plant P, but the mechanisms underlying P loading into the grains are poorly understood. We functionally characterized a transporter gene required for the distribution of P to the grains in barley (Hordeum vulgare), HvSPDT (SULTR-like phosphorus distribution transporter). HvSPDT encoded a plasma membrane-localized Pi/H+ cotransporter. It was mainly expressed in the nodes at both the vegetative and reproductive stages. Furthermore, its expression was induced by inorganic phosphate (Pi) deficiency. In the nodes, HvSPDT was expressed in both the xylem and phloem region of enlarged and diffuse vascular bundles. Knockout of HvSPDT decreased the distribution of P to new leaves, but increased the distribution to old leaves at the vegetative growth stage under low P supply. However, knockout of HvSPDT did not alter the redistribution of P from old to young organs. At the reproductive stage, knockout of HvSPDT significantly decreased P allocation to the grains, resulting in a considerable reduction in grain yield, especially under P-limited conditions. Our results indicate that node-based HvSPDT plays a crucial role in loading P into barley grains through preferentially distributing P from the xylem and further to the phloem.

DOI： 10.1111/nph.18057

Structural basis for high selectivity of a rice silicon channel Lsi1 査読国際誌

Yasunori Saitoh, Namiki Mitani-Ueno, Keisuke Saito, Kengo Matsuki, Sheng Huang, Lingli Yang, Naoki Yamaji, Hiroshi Ishikita, Jian-Ren Shen, Jian Feng Ma, Michihiro Suga

Nature Communications 12 ( 1 ) 6236 - 6236 2021年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media LLC

<title>Abstract</title>Silicon (Si), the most abundant mineral element in the earth’s crust, is taken up by plant roots in the form of silicic acid through Low silicon rice 1 (Lsi1). Lsi1 belongs to the Nodulin 26-like intrinsic protein subfamily in aquaporin and shows high selectivity for silicic acid. To uncover the structural basis for this high selectivity, here we show the crystal structure of the rice Lsi1 at a resolution of 1.8 Å. The structure reveals transmembrane helical orientations different from other aquaporins, characterized by a unique, widely opened, and hydrophilic selectivity filter (SF) composed of five residues. Our structural, functional, and theoretical investigations provide a solid structural basis for the Si uptake mechanism in plants, which will contribute to secure and sustainable rice production by manipulating Lsi1 selectivity for different metalloids.

DOI： 10.1038/s41467-021-26535-x

その他リンク： https://www.nature.com/articles/s41467-021-26535-x

A Low Level of NaCl Stimulates Plant Growth by Improving Carbon and Sulfur Assimilation in Arabidopsis thaliana 査読

Li Hongqiao, Akiko Suyama, Namiki Mitani-Ueno, Ruediger Hell, Akiko Maruyama-Nakashita

Plants 10 ( 10 ) 2138 - 2138 2021年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：MDPI AG

High-salinity stress represses plant growth by inhibiting various metabolic processes. In contrast to the well-studied mechanisms mediating tolerance to high levels of salt, the effects of low levels of salts have not been well studied. In this study, we examined the growth of Arabidopsis thaliana plants under different NaCl concentrations. Interestingly, both shoot and root biomass increased in the presence of 5 mM NaCl, whereas more than 10 mM NaCl decreased plant biomass. To clarify the biological mechanism by which a low level of NaCl stimulated plant growth, we analyzed element accumulation in plants grown under different NaCl concentrations. In addition to the Na and Cl contents, C, S, Zn, and Cu contents were increased under 5 mM NaCl in shoots; this was not observed at higher NaCl concentrations. Adverse effects of high salinity, such as decreased levels of nitrate, phosphate, sulfate, and some cations, did not occur in the presence of 5 mM NaCl. An increase in C was possibly attributed to increased photosynthesis supported by Cl, Zn, and Cu, which also increased in shoots after NaCl application. Salt stress-responsive gene expression was enhanced under 20 mM NaCl but not at lower doses. Among the S metabolites analyzed, cysteine (Cys) was increased by 5 mM NaCl, suggesting that S assimilation was promoted by this dose of NaCl. These results indicate the usefulness of NaCl for plant growth stimulation.

DOI： 10.3390/plants10102138

Linking transport system of silicon with its accumulation in different plant species 招待査読

Namiki Mitani-Ueno, Jian Feng Ma

Soil Science and Plant Nutrition 67 ( 1 ) 10 - 17 2021年1月

掲載種別：研究論文（学術雑誌）出版者・発行元：Informa UK Limited

Silicon (Si) is a beneficial element for plants, which helps to mitigate various biotic and abiotic stresses. Since the last review on Si published in this journal in 2004, great progress has been made in understanding transport system of Si in different plant species. The discovery of two different transporters for Si (Lsi1 and Lsi2) in rice led to intensive investigation of Si transporters in other plant species. Lsi1 belongs to the Nodulin 26-like intrinsic proteins (NIPs) subfamily in the aquaporin (AQP) family and functions as an influx transporter for Si. By contrast, Lsi2 belongs to the anion transporter superfamily and functions as an efflux transporter of Si. They are polarly localized at the distal and proximal sides, respectively, of both exodermis and endodermis of rice roots and are required for efficient uptake of Si. So far, homologs of Lsi1 and Lsi2 are identified not only in monocots, but also in dicots, which greatly differ in Si accumulation in the aboveground parts. However, the expression pattern, cell-type-specific expression, and polar localization of these transporters differ with plant species. In this review, we focus on recent progress in Si transporters identified in different plant species. We link these transporters with an accumulation of Si in different plant species in terms of expression pattern, cell-type-specific expression, polar localization of these transporters and propose three uptake systems of Si in different plant species. We also provide the perspectives toward a better understanding of Si transport system in different plant species and discuss its essentiality for plant growth.

DOI： 10.1080/00380768.2020.1845972

The grapevine NIP2;1 aquaporin is a silicon channel 査読

Henrique Noronha, Angelica Silva, Namiki Mitani-Ueno, Carlos Conde, Farzana Sabir, Catarina Prista, Graca Soveral, Paul Isenring, Jian Feng Ma, Richard R. Belanger, Hernani Geros

JOURNAL OF EXPERIMENTAL BOTANY 71 ( 21 ) 6789 - 6798 2020年12月

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) supplementation has been shown to improve plant tolerance to different stresses, and its accumulation in the aerial organs is mediated by NIP2;1 aquaporins (Lsi channels) and Lsi2-type exporters in roots. In the present study, we tested the hypothesis that grapevine expresses a functional NIP2;1 that accounts for root Si uptake and, eventually, Si accumulation in leaves. Own-rooted grapevine cuttings of the cultivar Vinhao accumulated >0.2% Si (DW) in leaves when irrigated with 1.5 mM Si for 1 month, while Si was undetected in control leaves. Real-time PCR showed that VvNIP2;1 was highly expressed in roots and in green berries. The transient transformation of tobacco leaf epidermal cells mediated by Agrobacterium tumefaciens confirmed VvNIP2;1 localization at the plasma membrane. Transport experiments in oocytes showed that VvNIP2;1 mediates Si and arsenite uptake, whereas permeability studies revealed that VvNIP2;1 expressed in yeast is unable to transport water and glycerol. Si supplementation to pigmented grape cultured cells (cv. Gamay Freaux) had no impact on the total phenolic and anthocyanin content, or on the growth rate and VvNIP2;1 expression. Long-term experiments should help determine the extent of Si uptake over time and whether grapevine can benefit from Si fertilization.

DOI： 10.1093/jxb/eraa294

Node-Localized Transporters of Phosphorus Essential for Seed Development in Rice. 査読

Jing Che, Naoki Yamaji, Takaaki Miyaji, Namiki Mitani-Ueno, Yuri Kato, Ren Fang Shen, Jian Feng Ma

Plant & cell physiology 61 ( 8 ) 1387 - 1398 2020年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

About 60-85% of total phosphorus (P) in cereal crops is finally allocated to seeds, where it is required for seed development, germination and early growth. However, little is known about the molecular mechanisms underlying P allocation to seeds. Here, we found that two members (OsPHO1;1 and OsPHO1;2) of the PHO1 gene family are involved in the distribution of P to seeds in rice. Both OsPHO1;1 and OsPHO1;2 were localized to the plasma membrane and showed influx transport activities for inorganic phosphate. At the reproductive stage, both OsPHO1;1 and OsPHO1;2 showed higher expression in node I, the uppermost node connecting to the panicle. OsPHO1;1 was mainly localized at the phloem region of diffuse vascular bundles (DVBs) of node I, while OsPHO1;2 was expressed in the xylem parenchyma cells of the enlarged vascular bundles (EVBs). In addition, they were also expressed in the ovular vascular trace, the outer layer of the inner integument (OsPHO1;1) and in the nucellar epidermis (OsPHO1;2) of caryopses. Knockout of OsPHO1;2, as well as OsPHO1;1 to a lesser extent, decreased the distribution of P to the seed, resulting in decreased seed size and delayed germination. Taken together, OsPHO1;2 expressed in node I is responsible for the unloading of P from the xylem of EVBs, while OsPHO1;1 is involved in reloading P into the phloem of DVBs for subsequent allocation of P to seeds. Furthermore, OsPHO1;1 and OsPHO1;2 expression in the caryopsis is important for delivering P from the maternal tissues to the filial tissues for seed development.

DOI： 10.1093/pcp/pcaa074

The ZIP Transporter Family Member OsZIP9 Contributes To Root Zinc Uptake in Rice under Zinc-Limited Conditions(1)([OPEN]) 査読

Sheng Huang, Akimasa Sasaki, Naoki Yamaji, Haruka Okada, Namiki Mitani-Ueno, Jian Feng Ma

PLANT PHYSIOLOGY 183 ( 3 ) 1224 - 1234 2020年7月

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 INC

Zinc (Zn) is an important essential micronutrient for plants and humans; however, the exact transporter responsible for root zinc uptake from soil has not been identified. Here, we found that OsZIP9, a member of the ZRT-IRT-related protein, is involved in Zn uptake in rice (Oryza sativa) under Zn-limited conditions. OsZIP9 was mainly localized to the plasma membrane and showed transport activity for Zn in yeast (Saccharomyces cerevisiae). Expression pattern analysis showed thatOsZIP9was mainly expressed in the roots throughout all growth stages and its expression was upregulated by Zn-deficiency. Furthermore,OsZIP9was expressed in the exodermis and endodermis of root mature regions. For plants grown in a hydroponic solution with low Zn concentration, knockout ofOsZIP9significantly reduced plant growth, which was accompanied by decreased Zn concentrations in both the root and shoot. However, plant growth and Zn accumulation did not differ between knockout lines and wild-type rice under Zn-sufficient conditions. When grown in soil, Zn concentrations in the shoots and grains of knockout lines were decreased to half of wild-type rice, whereas the concentrations of other mineral nutrients were not altered. A short-term kinetic experiment with stable isotope(67)Zn showed that(67)Zn uptake in knockout lines was much lower than that in wild-type rice. Combined, these results indicate that OsZIP9 localized at the root exodermis and endodermis functions as an influx transporter of Zn and contributes to Zn uptake under Zn-limited conditions in rice.The zinc transporter OsZIP9, expressed at the exodermis and endodermis of root mature region, contributes to Zn uptake from soil in rice.

DOI： 10.1104/pp.20.00125

Tomato roots have a functional silicon influx transporter but not a functional silicon efflux transporter 査読

Hao Sun, Yaoke Duan, Namiki Mitani-Ueno, Jing Che, Jianhua Jia, Jiaqi Liu, Jia Guo, Jian Feng Ma, Haijun Gong

PLANT CELL AND ENVIRONMENT 43 ( 3 ) 732 - 744 2020年3月

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

Silicon (Si) accumulation in shoots differs greatly with plant species, but the molecular mechanisms for this interspecific difference are unknown. Here, we isolated homologous genes of rice Si influx (SlLsi1) and efflux (SlLsi2) transporter genes in tomato (Solanum lycopersicum L.) and functionally characterized these genes. SlLsi1 showed transport activity for Si when expressed in both rice lsi1 mutant and Xenopus laevis oocytes. SlLsi1 was constitutively expressed in the roots. Immunostaining showed that SlLsi1 was localized at the plasma membrane of both root tip and basal region without polarity. Furthermore, overexpression of SlLsi1 in tomato increased Si concentration in the roots and root cell sap but did not alter the Si concentration in the shoots. By contrast, two Lsi2-like proteins did not show efflux transport activity for Si in Xenopus oocytes. However, when functional CsLsi2 from cucumber was expressed in tomato, the Si uptake was significantly increased, resulting in higher Si accumulation in the leaves and enhanced tolerance of the leaves to water deficit and high temperature. Our results suggest that the low Si accumulation in tomato is attributed to the lack of functional Si efflux transporter Lsi2 required for active Si uptake although SlLsi1 is functional.

DOI： 10.1111/pce.13679

Functional evolution of nodulin 26-like intrinsic proteins: from bacterial arsenic detoxification to plant nutrient transport 査読

Benjamin Pommerrenig, Till A. Diehn, Nadine Bernhardt, Manuela D. Bienert, Namiki Mitani-Ueno, Jacqueline Fuge, Annett Bieber, Christoph Spitzer, Andrea Braeutigam, Jian Feng Ma, Francois Chaumont, Gerd P. Bienert

NEW PHYTOLOGIST 225 ( 3 ) 1383 - 1396 2020年2月

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

Nodulin 26-like intrinsic proteins (NIPs) play essential roles in transporting the nutrients silicon and boron in seed plants, but the evolutionary origin of this transport function and the co-permeability to toxic arsenic remains enigmatic. Horizontal gene transfer of a yet uncharacterised bacterial AqpN-aquaporin group was the starting-point for plant NIP evolution. We combined intense sequence, phylogenetic and genetic context analyses and a mutational approach with various transport assays in oocytes and plants to resolve the transorganismal and functional evolution of bacterial and algal and terrestrial plant NIPs and to reveal their molecular transport specificity features. We discovered that aqpN genes are prevalently located in arsenic resistance operons of various prokaryotic phyla. We provided genetic and functional evidence that these proteins contribute to the arsenic detoxification machinery. We identified NIPs with the ancestral bacterial AqpN selectivity filter composition in algae, liverworts, moss, hornworts and ferns and demonstrated that these archetype plant NIPs and their prokaryotic progenitors are almost impermeable to water and silicon but transport arsenic and boron. With a mutational approach, we demonstrated that during evolution, ancestral NIP selectivity shifted to allow subfunctionalisations. Together, our data provided evidence that evolution converted bacterial arsenic efflux channels into essential seed plant nutrient transporters.

DOI： 10.1111/nph.16217

Vascular Cambium-Localized AtSPDT Mediates Xylem-to-Phloem Transfer of Phosphorus for Its Preferential Distribution in Arabidopsis 査読

Guangda Ding, Gui Jie Lei, Naoki Yamaji, Kengo Yokosho, Namiki Mitani-Ueno, Sheng Huang, Jian Feng Ma

MOLECULAR PLANT 13 ( 1 ) 99 - 111 2020年1月

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

During plant growth and development mineral elements are preferentially delivered to different organs and tissues to meet the differential demand. It has been shown that the preferential distribution of mineral nutrients in gramineous plants is mediated by node-based transporters, but the mechanisms of preferential distribution in dicots are poorly understood. Here, we report a distinct mechanism for the preferential distribution of phosphorus (P) in Arabidopsis plants, revealed by detailed functional analysis of AtSPDT/AtSULTR3;4 (SULTR-like P Distribution Transporter), a homolog of rice OsSPDT. Like OsSPDT, AtSPDT is localized at the plasma membrane and showed proton-dependent transport activity for P. Interestingly, we found that AtSPDT is mainly expressed in the rosette basal region and leaf petiole, and its expression is up-regulated by P deficiency. Tissue-specific analysis showed that AtSPDT is mainly located in the vascular cambium of different organs, as well as in the parenchyma tissues of both xylem and phloem regions. Knockout of AtSPDT inhibited the growth of new leaves under low P due to decreased P distribution to those organs. The seed yields of the wild-type and atspdt mutant plants are similar, but the seeds of mutant plants contain - less P. These results indicate that AtSPDT localized in the vascular cambium is involved in preferential distribution of P to the developing tissues, through xylem-to-phloem transfer mainly at the rosette basal region and leaf petiole.

DOI： 10.1016/j.molp.2019.10.002

Transport system of mineral elements in rice 査読

Namiki Mitani-Ueno, Naoki Yamaji, Jian Feng Ma

Rice Genomics, Genetics and Breeding 223 - 240 2018年3月

記述言語：英語掲載種別：論文集(書籍)内論文出版者・発行元：Springer Singapore

Plant requires 14 mineral elements for their growth and development. These elements in the soil are taken up by the roots, translocated from the roots to the shoots, and distributed to different organs depending on their demands (Marschner P, Mineral nutrition of higher plants, 3rd edn. Academic, London, 2012). In addition to these essential elements, toxic elements such as Cd and As are also transported from the soils to aboveground parts. All these processes require various transporters (membrane proteins). During the last decades, a number of transporters for uptake, translocation, and distribution of mineral elements have been identified, especially in model plants such as Arabidopsis and rice
however, most transporters remain to be identified. In this chapter, transporters identified so far in rice are described, and the regulation mechanisms of transporters in response to environmental changes are also discussed.

DOI： 10.1007/978-981-10-7461-5_13

The tonoplast-localized transporter MTP8.2 contributes to manganese detoxification in the shoots and roots of oryza sativa L. 査読

Yuma Takemoto, Yuta Tsunemitsu, Miho Fujii-Kashino, Namiki Mitani-Ueno, Naoki Yamaji, Jian Feng Ma, Shin Ichiro Kato, Kozo Iwasaki, Daisei Ueno

Plant and Cell Physiology 58 ( 9 ) 1573 - 1582 2017年9月

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

A model of silicon dynamics in rice: An analysis of the investment efficiency of Si transporters 査読

Gen Sakurai, Naoki Yamaji, Namiki Mitani-Ueno, Masayuki Yokozawa, Keisuke Ono, Jian Feng Ma

Frontiers in Plant Science 8 E31-E34 2017年7月

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 S.A.

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/fpls.2017.01187

A Model of Silicon Dynamics in Rice: An Analysis of the Investment Efficiency of Si Transporters 査読

Gen Sakurai, Naoki Yamaji, Namiki Mitani-Ueno, Masayuki Yokozawa, Keisuke Ono, Jian Feng Ma

FRONTIERS IN PLANT SCIENCE 8 2017年7月

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

Identification of a mammalian silicon transporter 査読

Sarah Ratcliffe, Ravin Jugdaohsingh, Julien Vivancos, Alan Marron, Rupesh Deshmukh, Jian Feng Ma, Namiki Mitani-Ueno, Jack Robertson, John Wills, Mark V. Boekschoten, Michael Mueller, Robert C. Mawhinney, Stephen D. Kinrade, Paul Isenring, Richard R. Belanger, Jonathan J. Powell

AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY 312 ( 5 ) C550 - C561 2017年5月

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 PHYSIOLOGICAL SOC

Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter OsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular HPO42- or Na+ concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon.

DOI： 10.1152/ajpcell.00219.2015

Polar Localization of the NIP5;1 Boric Acid Channel Is Maintained by Endocytosis and Facilitates Boron Transport in Arabidopsis Roots 査読

Sheliang Wang, Akira Yoshinari, Tomoo Shimada, Ikuko Hara-Nishimura, Namiki Mitani-Ueno, Jian Feng Ma, Satoshi Naito, Junpei Takano

PLANT CELL 29 ( 4 ) 824 - 842 2017年4月

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

Boron uptake in Arabidopsis thaliana is mediated by nodulin 26-like intrinsic protein 5;1 (NIP5;1), a boric acid channel that is located preferentially on the soil side of the plasma membrane in root cells. However, the mechanism underlying this polar localization is poorly understood. Here, we show that the polar localization of NIP5;1 in epidermal and endodermal root cells is mediated by the phosphorylation of Thr residues in the conserved TPG (ThrProGly) repeat in the N-terminal region of NIP5;1. Although substitutions of Ala for three Thr residues in the TPG repeat did not affect lateral diffusion in the plasma membrane, these substitutions inhibited endocytosis and strongly compromised the polar localization of GFP-NIP5;1. Consistent with this, the polar localization was compromised in m subunit mutants of the clathrin adaptor AP2. The Thr-to-Ala substitutions did not affect the boron transport activity of GFP-NIP5;1 in Xenopus laevis oocytes but did inhibit the ability to complement boron translocation to shoots and rescue growth defects in nip5;1-1 mutant plants under boron-limited conditions. These results demonstrate that the polar localization of NIP5;1 is maintained by clathrin-mediated endocytosis, is dependent on phosphorylation in the TPG repeat, and is necessary for the efficient transport of boron in roots.

DOI： 10.1105/tpc.16.00825

Reducing phosphorus accumulation in rice grains with an impaired transporter in the node (vol 541, pg 92, 2017) 査読

Naoki Yamaji, Yuma Takemoto, Takaaki Miyaji, Namiki Mitani-Ueno, Kaoru T. Yoshida, Jian Feng Ma

NATURE 541 ( 7635 ) 136 - 136 2017年1月

High Silicon Accumulation in the Shoot is Required for Down-Regulating the Expression of Si Transporter Genes in Rice 査読

Namiki Mitani-Ueno, Naoki Yamaji, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 57 ( 12 ) 2510 - 2518 2016年12月

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

An Aluminum-Inducible IREG Gene is Required for Internal Detoxification of Aluminum in Buckwheat 査読

Kengo Yokosho, Naoki Yamaji, Namiki Mitani-Ueno, Ren Fang Shen, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 57 ( 6 ) 1169 - 1178 2016年6月

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

A node-localized transporter OsZIP3 is responsible for the preferential distribution of Zn to developing tissues in rice 査読

Akimasa Sasaki, Naoki Yamaji, Namiki Mitani-Ueno, Miho Kashino, Jian Feng Ma

PLANT JOURNAL 84 ( 2 ) 374 - 384 2015年10月

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

Orchestration of three transporters and distinct vascular structures in node for intervascular transfer of silicon in rice 査読

Naoki Yamaji, Gen Sakurai, Namiki Mitani-Ueno, Jian Feng Ma

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 112 ( 36 ) 11401 - 11406 2015年9月

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

In Silico Simulation Modeling Reveals the Importance of the Casparian Strip for Efficient Silicon Uptake in Rice Roots 査読

Gen Sakurai, Akiko Satake, Naoki Yamaji, Namiki Mitani-Ueno, Masayuki Yokozawa, Francois Gabriel Feugier, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 56 ( 4 ) 631 - 639 2015年4月

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

A small RNA mediated regulation of a stress-activated retrotransposon and the tissue specific transposition during the reproductive period in Arabidopsis 査読

Wataru Matsunaga, Naohiko Ohama, Noriaki Tanabe, Yukari Masuta, Seiji Masuda, Namiki Mitani, Kazuko Yamaguchi-Shinozaki, Jian F. Ma, Atsushi Kato, Hidetaka Ito

FRONTIERS IN PLANT SCIENCE 6 48 2015年2月

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 RESEARCH FOUNDATION

Transposable elements (TEs) are key elements that facilitate genome evolution of the host organism. A number of studies have assessed the functions of TEs, which change gene expression in the host genome. Activation of TEs is controlled by epigenetic modifications such as DNA methylation and histone modifications. Several recent studies have reported that TEs can also be activated by biotic or abiotic stress in some plants. We focused on a Ty1/copia retrotransposon, ONSEN, that is activated by heat stress (HS) in Arabidopsis. We found that transcriptional activation of ONSEN was regulated by a small interfering RNA (siRNA)-related pathway, and the activation could also be induced by oxidative stress. Mutants deficient in siRNA biogenesis that were exposed to HS at the initial stages of vegetative growth showed transgenerational transposition. The transposition was also detected in the progeny, which originated from tissue that had differentiated after exposure to the HS. The results indicated that in some undifferentiated cells, transpositional activity could be maintained quite long after exposure to the HS.

DOI： 10.3389/fpls.2015.00048

Transcriptional activity and silencing of heat activated retrotransposon in Arabidopsis 査読

Wataru Matsunaga, Yukari Masuta, Namiki Mitani, Ma Jian Feng, Atsushi Kato, Hidetaka Ito

GENES & GENETIC SYSTEMS 89 ( 6 ) 316 - 316 2014年12月

Physiological and molecular characterization of Si uptake in wild rice species 査読

Namiki Mitani-Ueno, Hisao Ogai, Naoki Yamaji, Jian Feng Ma

PHYSIOLOGIA PLANTARUM 151 ( 3 ) 200 - 207 2014年7月

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

Root and shoot transcriptome analysis of two ecotypes of Noccaea caerulescens uncovers the role of NcNramp1 in Cd hyperaccumulation 査読

Matthew J. Milner, Namiki Mitani-Ueno, Naoki Yamaji, Kengo Yokosho, Eric Craft, Zhangjun Fei, Stephen Ebbs, M. Clemencia Zambrano, Jian Feng Ma, Leon V. Kochian

PLANT JOURNAL 78 ( 3 ) 398 - 410 2014年5月

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

Preferential Delivery of Zinc to Developing Tissues in Rice Is Mediated by P-Type Heavy Metal ATPase OsHMA2 査読

Naoki Yamaji, Jixing Xia, Namiki Mitani-Ueno, Kengo Yokosho, Jian Feng Ma

PLANT PHYSIOLOGY 162 ( 2 ) 927 - 939 2013年6月

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

Functional Characterization of a Silicon Transporter Gene Implicated in Silicon Distribution in Barley 査読

Naoki Yamaji, Yukako Chiba, Namiki Mitani-Ueno, Jian Feng Ma

PLANT PHYSIOLOGY 160 ( 3 ) 1491 - 1497 2012年11月

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

Cloning, functional characterization and heterologous expression of TaLsi1, a wheat silicon transporter gene 査読

Jonatan Montpetit, Julien Vivancos, Namiki Mitani-Ueno, Naoki Yamaji, Wilfried Remus-Borel, Francois Belzile, Jian Feng Ma, Richard R. Belanger

PLANT MOLECULAR BIOLOGY 79 ( 1-2 ) 35 - 46 2012年5月

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

The aromatic/arginine selectivity filter of NIP aquaporins plays a critical role in substrate selectivity for silicon, boron, and arsenic 査読

Namiki Mitani-Ueno, Naoki Yamaji, Fang-Jie Zhao, Jian Feng Ma

JOURNAL OF EXPERIMENTAL BOTANY 62 ( 12 ) 4391 - 4398 2011年8月

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

The aromatic/arginine selectivity filter of NIP aquaporins plays a critical role in substrate selectivity for silicon, boron, and arsenic 査読

Namiki Mitani-Ueno, Naoki Yamaji, Fang-Jie Zhao, Jian Feng Ma

JOURNAL OF EXPERIMENTAL BOTANY 62 ( 12 ) 4391 - 4398 2011年8月

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

Isolation and functional characterization of an influx silicon transporter in two pumpkin cultivars contrasting in silicon accumulation. 査読

Mitani N, Yamaji N, Ago Y, Iwasaki K, Ma JF

The Plant journal : for cell and molecular biology 66 ( 2 ) 231 - 240 2011年4月

Isolation and functional characterization of an influx silicon transporter in two pumpkin cultivars contrasting in silicon accumulation 査読

Namiki Mitani, Naoki Yamaji, Yukiko Ago, Kozo Iwasaki, Jian Feng Ma

PLANT JOURNAL 66 ( 2 ) 231 - 240 2011年4月

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

Silicon efflux transporters isolated from two pumpkin cultivars contrasting in Si uptake 査読

Namiki Mitani-Ueno, Naoki Yamaji, Jian Feng Ma

Plant Signaling and Behavior 6 ( 7 ) 73 - 76 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）

The accumulation of silicon (Si) differs greatly with plant species and cultivars due to different ability of the roots to take up Si. In Si accumulating plants such as rice, barley and maize, Si uptake is mediated by the influx (Lsi1) and efflux (Lsi2) transporters. Here we report isolation and functional analysis of two Si efflux transporters (CmLsi2-1 and CmLsi2-2) from two pumpkin (Cucurbita moschata Duch.) cultivars contrasting in Si uptake. These cultivars are used for rootstocks of bloom and bloomless cucumber, respectively. Different from mutations in the Si influx transporter CmLsi1, there was no difference in the sequence of either CmLsi2 between two cultivars. Both CmLsi2-1 and CmLsi2-2 showed an efflux transport activity for Si and they were expressed in both the roots and shoots. These results confirm our previous finding that mutation in CmLsi1, but not in CmLsi2-1 and CmLsi2-2 are responsible for bloomless phenotype resulting from low Si uptake. © 2011 Landes Bioscience.

DOI： 10.4161/psb.6.7.15462

Transport of silicon from roots to panicles in plants 査読

Jian Feng Ma, Naoki Yamaji, Namiki Mitani-Ueno

Proceedings of the Japan Academy Series B: Physical and Biological Sciences 87 ( 7 ) 377 - 385 2011年

記述言語：英語

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. © 2011 The Japan Academy.

DOI： 10.2183/pjab.87.377

Involvement of Silicon Influx Transporter OsNIP2;1 in Selenite Uptake in Rice 査読

Xue Qiang Zhao, Namiki Mitani, Naoki Yamaji, Ren Fang Shen, Jian Feng Ma

PLANT PHYSIOLOGY 153 ( 4 ) 1871 - 1877 2010年8月

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

The role of the rice aquaporin Lsi1 in arsenite efflux from roots 査読

Fang-Jie Zhao, Yukiko Ago, Namiki Mitani, Ren-Ying Li, Yu-Hong Su, Naoki Yamaji, Steve P. McGrath, Jian Feng Ma

NEW PHYTOLOGIST 186 ( 2 ) 392 - 399 2010年

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

The Rice Aquaporin Lsi1 Mediates Uptake of Methylated Arsenic Species 査読

Ren-Ying Li, Yukiko Ago, Wen-Ju Liu, Namiki Mitani, Joerg Feldmann, Steve P. McGrath, Jian Feng Ma, Fang-Jie Zhao

PLANT PHYSIOLOGY 150 ( 4 ) 2071 - 2080 2009年8月

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

Pentavalent methylated arsenic (As) species such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] are used as herbicides or pesticides, and can also be synthesized by soil microorganisms or algae through As methylation. The mechanism of MMA(V) and DMA(V) uptake remains unknown. Recent studies have shown that arsenite is taken up by rice (Oryza sativa) roots through two silicon transporters, Lsi1 (the aquaporin NIP2;1) and Lsi2 (an efflux carrier). Here we investigated whether these two transporters also mediate the uptake of MMA(V) and DMA(V). MMA(V) was partly reduced to trivalent MMA(III) in rice roots, but only MMA(V) was translocated to shoots. DMA(V) was stable in plants. The rice lsi1 mutant lost about 80% and 50% of the uptake capacity for MMA(V) and DMA(V), respectively, compared with the wild-type rice, whereas Lsi2 mutation had little effect. The short-term uptake kinetics of MMA(V) can be described by a Michaelis-Menten plus linear model, with the wild type having 3.5-fold higher V(max) than the lsi1 mutant. The uptake kinetics of DMA(V) were linear with the slope being 2.8-fold higher in the wild type than the lsi1 mutant. Heterologous expression of Lsi1 in Xenopus laevis oocytes significantly increased the uptake of MMA(V) but not DMA(V), possibly because of a very limited uptake of the latter. Uptake of MMA(V) and DMA(V) by wild-type rice was increased as the pH of the medium decreased, consistent with an increasing proportion of the undissociated species. The results demonstrate that Lsi1 mediates the uptake of undissociated methylated As in rice roots.

DOI： 10.1104/pp.109.140350

Identification and Characterization of Maize and Barley Lsi2-Like Silicon Efflux Transporters Reveals a Distinct Silicon Uptake System from That in Rice 査読

Namiki Mitani, Yukako Chiba, Naoki Yamaji, Jian Feng Ma

PLANT CELL 21 ( 7 ) 2133 - 2142 2009年7月

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

HvLsi1 is a silicon influx transporter in barley. 査読

Chiba Y, Mitani N, Yamaji N, Ma JF

The Plant journal : for cell and molecular biology 57 ( 5 ) 810 - 818 2009年3月

A Bacterial-Type ABC Transporter Is Involved in Aluminum Tolerance in Rice 査読

Chao Feng Huang, Naoki Yamaji, Namiki Mitani, Masahiro Yano, Yoshiaki Nagamura, Jian Feng Ma

PLANT CELL 21 ( 2 ) 655 - 667 2009年2月

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

OsFRDL1 Is a Citrate Transporter Required for Efficient Translocation of Iron in Rice 査読

Kengo Yokosho, Naoki Yamaji, Daisei Ueno, Namiki Mitani, Jian Feng Ma

PLANT PHYSIOLOGY 149 ( 1 ) 297 - 305 2009年1月

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

Identification of Maize Silicon Influx Transporters 査読

Namiki Mitani, Naoki Yamaji, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 50 ( 1 ) 5 - 12 2009年1月

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

NIP1;1, an Aquaporin Homolog, Determines the Arsenite Sensitivity of Arabidopsis thaliana 査読

Takehiro Kamiya, Mayuki Tanaka, Namiki Mitani, Jian Feng Ma, Masayoshi Maeshima, Toru Fujiwara

JOURNAL OF BIOLOGICAL CHEMISTRY 284 ( 4 ) 2114 - 2120 2009年1月

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 BIOCHEMISTRY MOLECULAR BIOLOGY INC

Arsenite [As(III)] is highly toxic to organisms, including plants. Very recently, transporters in rice responsible for As(III) transport have been described (Ma, J. F., Yamaji, N., Mitani, N., Xu, X. Y., Su, Y. H., McGrath, S. P., and Zhao, F. J. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 9931-9935), but little is known about As(III) tolerance. In this study, three independent As(III)-tolerant mutants were isolated from ethyl methanesulfonate-mutagenized M2 seeds of Arabidopsis thaliana. All three mutants carried independent mutations in Nodulin 26-like intrinsic protein 1;1 (NIP1;1), a homolog of an aquaporin. Two independent transgenic lines carrying T-DNA in NIP1; 1 were highly tolerant to As(III), establishing that NIP1;1 is the causal gene of As(III) tolerance. Because an aquaglyceroporin is able to transport As(III), we measured As(III) transport activity. When expressed in Xenopus oocytes, NIP1; 1 was capable of transporting As(III). As content in the mutant plants was 30% lower than in wild-type plants. Promoter beta-glucuronidase and real-time PCR analysis showed that NIP1; 1 is highly expressed in roots, and GFP-NIP1;1 is localized to the plasma membrane. These data show that NIP1; 1 is involved in As(III) uptake into roots and that disruption of NIP1; 1 function confers As(III) tolerance to plants. NIP1;2 and NIP5;1, closely related homologs of NIP1;1, were also permeable to As(III). Although the disruption of these genes reduced the As content in plants, As(III) tolerance was not observed in nip1;2 and nip5;1 mutants. This indicates that As(III) tolerance cannot be simply explained by decreased As contents in plants.

DOI： 10.1074/jbc.M806881200

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain 査読

Jian Feng Ma, Naoki Yamaji, Namiki Mitani, Xiao-Yan Xu, Yu-Hong Su, Steve P. McGrath, Fang-Jie Zhao

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 ( 29 ) 9931 - 9935 2008年7月

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

Characterization of substrate specificity of a rice silicon transporter, Lsi1 査読

Namiki Mitani, Naoki Yamaji, Jian Feng Ma

Pflugers Archiv European Journal of Physiology 456 ( 4 ) 679 - 686 2008年7月

記述言語：英語

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 HgCl2 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. © 2007 Springer-Verlag.

DOI： 10.1007/s00424-007-0408-y

Transcriptome analysis of the silicon-Magnaporthe grisea interaction

A. M. Brunings, L. E. Datnoff, J. F. Ma, N. Mitani, Y. Nagamura, B. Rathinasabapathi

PHYTOPATHOLOGY 98 ( 6 ) S28 - S28 2008年6月

Genotypic difference in silicon uptake and expression of silicon transporter genes in rice 査読

Jian Feng Ma, Naoki Yamaji, Kazunori Tamai, Namiki Mitani

PLANT PHYSIOLOGY 145 ( 3 ) 919 - 924 2007年11月

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

An aluminum-activated citrate transporter in barley. 査読

Jun Furukawa, Naoki Yamaji, Hua Wang, Namiki Mitani, Yoshiko Murata, Kazuhiro Sato, Maki Katsuhara, Kazuyoshi Takeda, Jian Feng Ma

Plant & cell physiology 48 ( 8 ) 1081 - 91 2007年8月

記述言語：英語

Soluble ionic aluminum (Al) inhibits root growth and reduces crop production on acid soils. Al-resistant cultivars of barley (Hordeum vulgare L.) detoxify Al by secreting citrate from the roots, but the responsible gene has not been identified yet. Here, we identified a gene (HvAACT1) responsible for the Al-activated citrate secretion by fine mapping combined with microarray analysis, using an Al-resistant cultivar, Murasakimochi, and an Al-sensitive cultivar, Morex. This gene belongs to the multidrug and toxic compound extrusion (MATE) family and was constitutively expressed mainly in the roots of the Al-resistant barley cultivar. Heterologous expression of HvAACT1 in Xenopus oocytes showed efflux activity for (14)C-labeled citrate, but not for malate. Two-electrode voltage clamp analysis also showed transport activity of citrate in the HvAACT1-expressing oocytes in the presence of Al. Overexpression of this gene in tobacco enhanced citrate secretion and Al resistance compared with the wild-type plants. Transiently expressed green fluorescent protein-tagged HvAACT1 was localized at the plasma membrane of the onion epidermal cells, and immunostaining showed that HvAACT1 was localized in the epidermal cells of the barley root tips. A good correlation was found between the expression of HvAACT1 and citrate secretion in 10 barley cultivars differing in Al resistance. Taken together, our results demonstrate that HvAACT1 is an Al-activated citrate transporter responsible for Al resistance in barley.

DOI： 10.1093/pcp/pcm091

An efflux transporter of silicon in rice 査読

Jian Feng Ma, Naoki Yamaji, Namiki Mitani, Kazunori Tamai, Saeko Konishi, Toru Fujiwara, Maki Katsuhara, Masahiro Yano

NATURE 448 ( 7150 ) 209 - U12 2007年7月

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

Characterization of silicon permeability of NIP in gramineous plants 査読

Namiki Mitani, Naoki Yamaji, Maki Katsuhara, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 48 S30 - S30 2007年

Functional analysis of a rice Si transporter homolog Lsi6. 査読

Naoki Yamaji, Namiki Mitani, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 48 S30 - S30 2007年

A silicon transporter in rice. 査読

Ma JF, Tamai K, Yamaji N, Mitani N, Konishi S, Katsuhara M, Ishiguro M, Murata Y, Yano M

Nature 440 ( 7084 ) 688 - 691 2006年3月

Identification of the silicon form in xylem sap of rice (Oryza sativa L.)

N Mitani, JF Ma, T Iwashita

PLANT AND CELL PHYSIOLOGY 46 ( 2 ) 279 - 283 2005年2月

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 (Oryza sativa L.) is a typical silicon (Si)-accumulating plant, but the mechanism responsible for the translocation from the root to the shoot is poorly understood. In this study, the form of Si in xylem sap was identified by 2 Si-29-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv. Oochikara) cultured in a monosilicic acid solution containing 0.5 mM Si, the Si concentration in the xylem reached 6 mM,l within 30 min. In the Si-29-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. A H-1-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the components of the xylem sap were not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.

DOI： 10.1093/pcp/pci018

Isolation and characterization of Lsi1 査読

Mitani N, Tamai K, Konishi S, Yano M, Yamaji N, Kyo M, Ma JF

Plant and Cell Physiology 46 S82 2005年

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