Faculty Profiles - MA Jian Feng

Papers - MA Jian Feng

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Identification of a Novel Major Quantitative Trait Locus Controlling Distribution of Cd Between Roots and Shoots in Rice

Daisei Ueno, Emi Koyama, Izumi Kono, Tsuyu Ando, Masahiro Yano, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 50 ( 12 ) 2223 - 2233 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

Accumulation of Cd in rice grain is a serious concern of food safety since rice as a staple food is a major source of Cd intake in Asian countries. However, the mechanisms controlling Cd accumulation in rice are still poorly understood. Herein, we report both physiological and genetic analysis of two rice cultivars contrasting in Cd accumulation, which were screened from a core collection of rice cultivars. The cultivar Anjana Dhan (Indica) accumulated much higher levels of Cd than Nipponbare (Japonica) in the shoots and grains when grown in both soil and solution culture. A short-term uptake experiment (20 min) showed that Cd uptake by Nipponbare was higher than that by Anjana Dhan. However, the concentration of Cd in the shoot and xylem sap was much higher in Anjana Dhan than in Nipponbare. Of the Cd taken up by the roots, <4% was translocated to the shoots in Nipponbare, compared with 10-25% in Anjana Dhan, indicating a higher root-to-shoot translocation of Cd in the latter. A quantitative trait locus (QTL) analysis for Cd accumulation was performed using an F-2 population derived from Anjana Dhan and Nipponbare. A QTL with large effect for Cd accumulation was detected on the short arm of chromosome 7, explaining 85.6 of the phenotypic variance in the shoot Cd concentration of the F-2 population. High accumulation is likely to be controlled by a single recessive gene. A candidate genomic region was defined to <1.9 Mb by means of substitution mapping.

DOI： 10.1093/pcp/pcp160

Iron for plants and humans

Jian Feng Ma, Hong-Qing Ling

PLANT AND SOIL 325 ( 1-2 ) 1 - 3 2009.12

A Zinc Finger Transcription Factor ART1 Regulates Multiple Genes Implicated in Aluminum Tolerance in Rice

Naoki Yamaji, Chao Feng Huang, Sakiko Nagao, Masahiro Yano, Yutaka Sato, Yoshiaki Nagamura, Jian Feng Ma

PLANT CELL 21 ( 10 ) 3339 - 3349 2009.10

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Secretion time of phytosiderophore differs in two perennial grasses and is controlled by temperature

Daisei Ueno, Jian Feng Ma

PLANT AND SOIL 323 ( 1-2 ) 335 - 341 2009.10

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Some perennial grasses secrete phytosiderophores from the roots in response to Fe-deficiency. Here, we characterized the pattern of phytosiderophore secretion by Lolium perenne (cv. 'Tove') and Poa pratensis (cv. 'Baron'), which are used to correct iron-deficiency induced chlorosis in fruit trees grown on calcareous soils. Both species showed a distinct diurnal rhythm in phytosiderophore secretion, but the secretion time differed between species; the secretion peak time was about 2 h earlier in L. perenne than in P. pratensis under the same growth conditions. The secretion time was shifted by changing temperature during the collection of phytosiderophores in both L. perenne and P. pratensis. Increasing root-zone temperature resulted in earlier secretion, while lowering the temperature resulted in delayed secretion. Furthermore, this shift of secretion time was achieved by changing the temperature around the root-zone. Shading treatment during the secretion period did not affect the secretion time in either species. These results indicate that the secretion of phytosiderophore is triggered by the temperature around the roots, but not light, in these two perennial grasses.

DOI： 10.1007/s11104-009-9962-8

A Transporter at the Node Responsible for Intervascular Transfer of Silicon in Rice

Naoki Yamaji, Jian Feng Ma

PLANT CELL 21 ( 9 ) 2878 - 2883 2009.9

Language：English Publishing type：Research paper (scientific journal) Publisher：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

The Rice Aquaporin Lsi1 Mediates Uptake of Methylated Arsenic Species

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 2009.8

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Effects of active silicon uptake by rice on Si-29 fractionation in various plant parts

Jan Reent Koester, Roland Bol, Melanie J. Leng, Adrian G. Parker, Hilary J. Sloane, Jian F. Ma

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 23 ( 16 ) 2398 - 2402 2009.8

Language：English Publishing type：Research paper (international conference proceedings) Publisher：WILEY-BLACKWELL

Rice (Oryza sativa L.) accumulates large amounts of silicon which improves its growth and health due to enhanced resistance to biotic and abiotic stresses. Silicon uptake and loading to xylem in rice are predominantly active processes performed by transporters encoded by the recently identified genes Lsi1 (Si influx transporter gene) and Lsi2 (Si efflux transporter gene). Silicon deposition in rice during translocation to upper plant tissues is known to discriminate against the heavier isotopes Si-29 and Si-30, resulting in isotope fractionation within the plant. We analyzed straw and husk samples of rice mutants defective in Lsi1, Lsi2 or both for silicon content and delta Si-29 using isotope ratio mass spectrometry (IRMS) and compared these results with those for the corresponding wild-type varieties (WT). The silicon content was higher in husk than in straw. All the mutant rice lines showed clearly lower silicon content than the WT lines (4-23% Si of WT). The delta Si-29 was lower in straw and husk for the uptake defective mutant (lsi1) than for WT, albeit delta Si-29 was 0.3 parts per thousand higher in husk than in straw in both lines. The effect of defective efflux (lsi2) differed for straw and husk with higher delta Si-29 in straw, but lower delta Si-29 in husk while WT showed similar delta Si-29 in both fractions. These initial results show the potential of Si isotopes to enlighten the influence of active uptake on translocation and deposition processes in the plant. Copyright (C) 2009 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.3971

Further characterization of ferric-phytosiderophore transporters ZmYS1 and HvYS1 in maize and barley

Daisei Ueno, Naoki Yamaji, Jian Feng Ma

JOURNAL OF EXPERIMENTAL BOTANY 60 ( 12 ) 3513 - 3520 2009.8

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

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

PLANT CELL 21 ( 7 ) 2133 - 2142 2009.7

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Arsenic transport in plants

Fangjie Zhao, Jian Feng Ma, Steve P. McGrath

COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY 153A ( 2 ) S187 - S187 2009.6

Mitigation of Arsenic Accumulation in Rice with Water Management and Silicon Fertilization

R. Y. Li, J. L. Stroud, J. F. Ma, S. P. McGrath, F. J. Zhao

ENVIRONMENTAL SCIENCE & TECHNOLOGY 43 ( 10 ) 3778 - 3783 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Rice represents a major route of As exposure in populations that depend on a rice diet. Practical measures are needed to mitigate the problem of excessive As accumulation in paddy rice. Two potential mitigation methods, management of the water regime and Si fertilization, were investigated under greenhouse conditions. Growing rice aerobically during the entire rice growth duration resulted in the leastAS accumulation. Maintaining aerobic conditions during either vegetative or reproductive stage of rice growth also decreased As accumulation in rice straw and grain significantly compared with rice grown under flooded conditions. The effect of water management regimes was consistent with the observed effect of flooding-induced arsenite mobilization in the soil solution. Aerobic treatments increased the percentage of inorganic As in grain, but the concentrations of inorganic As remained lower than in the flooded rice. Silicon fertilization decreased the total As concentration in straw and grain by 78 and 16%, respectively, even though Si addition increased As concentration in the soil solution. Silicon also significantly influenced As speciation in rice grain and husk by enhancing methylation. Silicon decreased the inorganic As concentration in grain by 59% while increasing the concentration of dimethylarsinic acid (DMA) by 33%. There were also significant differences between two rice genotypes in grain As speciation. This study demonstrated that water management, Si fertilization, and selection of rice cultivars are effective measures that can be used to reduce As accumulation in rice.

DOI： 10.1021/es803643v

A Rice Mutant Sensitive to Al Toxicity is Defective in the Specification of Root Outer Cell Layers

Chao-Feng Huang, Naoki Yamaji, Minoru Nishimura, Shigeyuki Tajima, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 50 ( 5 ) 976 - 985 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：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

HvLsi1 is a silicon influx transporter in barley

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

PLANT JOURNAL 57 ( 5 ) 810 - 818 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

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

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

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

PLANT CELL 21 ( 2 ) 655 - 667 2009.2

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

PLANT PHYSIOLOGY 149 ( 1 ) 297 - 305 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

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

JOURNAL OF BIOLOGICAL CHEMISTRY 284 ( 4 ) 2114 - 2120 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Defective Active Silicon Uptake Affects Some Components of Rice Resistance to Brown Spot

Leandro J. Dallagnol, Fabricio A. Rodrigues, Mateus V. B. Mielli, Jian F. Ma, Lawrence E. Datnoff

PHYTOPATHOLOGY 99 ( 1 ) 116 - 121 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYTOPATHOLOGICAL SOC

Rice is known to accumulate high amounts of silicon (Si) in plant tissue, which helps to decrease the intensity of many economically important rice diseases. Among these diseases, brown spot, caused by the fungus Bipolaris oryzae, is one of the most devastating because it negatively affects yield and grain quality. This study aimed to evaluate the importance of active root Si uptake in rice for controlling brown spot development. Some components of host resistance were evaluated in a rice mutant, low silicon 1 (lsi1), defective in active Si uptake, and its wild-type counterpart (cv. Oochikara). Plants were inoculated with B. oryzae after growing for 35 days in a hydroponic culture amended with 0 or 2 mMol Si. The components of host resistance evaluated were incubation period (IP), relative infection efficiency (RIE), area under brown spot progress curve (AUBSPC), final lesion size (FLS), rate of lesion expansion (r), and area under lesion expansion progress curve (AULEPC). Si content from both Oochikara and lsi1 in the +Si treatment increased in leaf tissue by 219 and 178%, respectively, over the nonamended controls. Plants from Oochikara had 112% more Si in leaf tissue than plants from lsi1. The IP of brown spot from Oochikara increased approximate to 6 h in the presence of Si and the RIE, AUBSPC, FLS, r, and AULEPC were significantly reduced by 65, 75, 33, 36, and 35%, respectively. In the presence of Si, the IP increased 3 h for lsi1 but the RIE, AUBSPC, FLS, r, and AULEPC were reduced by only 40, 50, 12, 21, and 12%, respectively. The correlation between Si leaf content and IP was significantly positive but Si content was negatively correlated with RIE, AUBSPC, FLS, r, and AULEPC. Single degree-of-freedom contrasts showed that Oochikara and lsi1 supplied with Si were significantly different from those not supplied with Si for all components of resistance evaluated. This result showed that a reduced Si content in tissues of plants from lsi1 dramatically affected its basal level of resistance to brown spot, suggesting that a minimum Si concentration is needed. Consequently, the results of this study emphasized the importance of an active root Si uptake system for an increase in rice resistance to brown spot.

DOI： 10.1094/PHYTO-99-1-0116

Identification of Maize Silicon Influx Transporters

Namiki Mitani, Naoki Yamaji, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 50 ( 1 ) 5 - 12 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Arsenic uptake and metabolism in plants

F. J. Zhao, J. F. Ma, A. A. Meharg, S. P. McGrath

NEW PHYTOLOGIST 181 ( 4 ) 777 - 794 2009

Language：English Publisher：WILEY-BLACKWELL PUBLISHING, INC

Arsenic (As) is an element that is nonessential for and toxic to plants. Arsenic contamination in the environment occurs in many regions, and, depending on environmental factors, its accumulation in food crops may pose a health risk to humans. Recent progress in understanding the mechanisms of As uptake and metabolism in plants is reviewed here. Arsenate is taken up by phosphate transporters. A number of the aquaporin nodulin26-like intrinsic proteins (NIPs) are able to transport arsenite, the predominant form of As in reducing environments. In rice (Oryza sativa), arsenite uptake shares the highly efficient silicon (Si) pathway of entry to root cells and efflux towards the xylem. In root cells arsenate is rapidly reduced to arsenite, which is effluxed to the external medium, complexed by thiol peptides or translocated to shoots. One type of arsenate reductase has been identified, but its in planta functions remain to be investigated. Some fern species in the Pteridaceae family are able to hyperaccumulate As in above-ground tissues. Hyperaccumulation appears to involve enhanced arsenate uptake, decreased arsenite-thiol complexation and arsenite efflux to the external medium, greatly enhanced xylem translocation of arsenite, and vacuolar sequestration of arsenite in fronds. Current knowledge gaps and future research directions are also identified.

DOI： 10.1111/j.1469-8137.2008.02716.x

A major quantitative trait locus controlling cadmium translocation in rice (Oryza sativa)

D. Ueno, I. Kono, K. Yokosho, T. Ando, M. Yano, J. F. Ma

NEW PHYTOLOGIST 182 ( 3 ) 644 - 653 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL PUBLISHING, INC

The trait of low cadmium (Cd) accumulation in brown rice (Oryza sativa) is important for food safety. An effective way to reduce Cd accumulation in the grain is to control Cd transfer from the roots to the shoots.
Here, we investigated genotypic variation in the shoot Cd concentration among 146 accessions from a rice core collection and performed a quantitative trait locus (QTL) analysis to determine the loci controlling shoot Cd accumulation. Furthermore, we physiologically characterized the two accessions used for QTL analysis.
Large genotypic variation (13-fold) in the shoot Cd concentration was found. A major QTL was detected on chromosome 11 using a F(2) population derived from Badari Dhan (a high-Cd accession) and Shwe War (a low-Cd accession). This QTL explained 16.1% of the phenotypic variation in Cd accumulation. Furthermore, this QTL was confirmed by analysis of advanced progeny. Physiological studies showed that Badari Dhan and Shwe War did not differ in uptake of Cd by the roots, but differed greatly in the translocation of Cd from the roots to the shoots.
Taken together, our findings suggest that the major QTL detected is responsible for the translocation of Cd from the roots to the shoots.
New Phytologist (2009) 182: 644-653doi: 10.1111/j.1469-8137.2009.02784.x.

DOI： 10.1111/j.1469-8137.2009.02784.x

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