Proceedings of the National Academy of Sciences Acta Medica Okayama 0027-8424 123 17 2026 A magnesium efflux transporter required for seed development and eating quality in rice e2536813123 EN Sheng Huang Institute of Plant Science and Resources, Okayama University Kiyosumi Hori National Institute of Crop Science, National Agriculture Research Organization Naoki Yamaji Institute of Plant Science and Resources, Okayama University Yuma Yoshioka Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Min Ning Institute of Plant Science and Resources, Okayama University Yu Nagaya Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Takaaki Miyaji Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Namiki Mitani-Ueno Institute of Plant Science and Resources, Okayama University Shin-ichiro Inoue Department of Regulatory Biology, Saitama University June-Sik Kim Institute of Plant Science and Resources, Okayama University Miho Kashino Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University As a staple food for half the world�fs population, rice is an important dietary source of magnesium (Mg), an essential mineral for human health. Enhanced Mg accumulation in rice grains has also been linked to eating quality. However, the mechanisms underlying Mg transport to the grains remains poorly understood. Here, we report that OsMGR2, a member belonging to Magnesium Release (MGR) family, is required for Mg accumulation in rice grains. OsMGR2 encodes a plasma membrane-localized transporter that mediates Mg efflux. OsMGR2 is constitutively and highly expressed in the stele tissues of roots, the phloem region of both enlarged and diffused vascular bundles in nodes, and the ovular vascular trace of caryopses. Knockout of this gene results in decreased root-to-shoot translocation and altered distribution of Mg to different organs; less Mg is allocated to the second newest leaf with high Mg requirement for active photosynthesis. The osmgr2 mutants exhibit decreased Mg accumulation in the grain, which are smaller, lighter, and shriveled, but show increased accumulation in the husk. The eating quality of the mutant grains is significantly decreased compared with the wild-type rice. These results indicate that OsMGR2 plays multiple roles within the rice; facilitating the root-to-shoot Mg translocation, mediating phloem-to-xylem Mg transfer at nodes for preferential distribution to the most active leaf, and exporting Mg from maternal vascular tissues of the caryopsis to the grains, processes essential for grain development and eating quality in rice. No potential conflict of interest relevant to this article was reported.

Oxford University Press (OUP) Acta Medica Okayama 0032-0889 198 1 2025 Role of polar localization of the silicon transporter OsLsi1 in metalloid uptake by rice roots kiaf196 EN Noriyuki Konishi Institute of Plant Science and Resources, Okayama University Namiki Mitani-Ueno Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Low silicon (Si) rice 1 (OsLsi1) is a key transporter mediating Si uptake in rice (Oryza sativa). It is polarly localized at the distal side of the root exodermis and endodermis. Although OsLsi1 is also permeable to other metalloids, such as boron (B), germanium (Ge), arsenic (As), antimony (Sb), and selenium (Se), the role of its polar localization in the uptake of these metalloids remains unclear. In this study, we investigated the role of OsLsi1 polar localization in metalloid uptake by examining transgenic rice plants expressing polarly or nonpolarly localized OsLsi1 variants. Loss of OsLsi1 polar localization resulted in decreased accumulation of Ge, B, and As in shoots but increased Sb accumulation, while Se accumulation remained unaffected under normal conditions. Experiments with varying B concentrations revealed that B uptake is significantly lower at low B concentrations (0.3 to 3 ��m) but higher at high B concentrations (300 ��m) in plants expressing nonpolarly localized OsLsi1, despite the similar B permeability of both OsLsi1 variants in Xenopus oocytes and their comparable protein abundance in roots. Additionally, the loss of OsLsi1 polarity did not affect the abundance, localization, or high B-induced degradation of the borate transporter 1 (OsBOR1), an efflux transporter that cooperates with OsLsi1 for B uptake. Taken together, our findings demonstrate that the polar localization of OsLsi1 plays a critical role in regulating metalloid uptake, depending on the presence or absence of efflux transporters cooperating with OsLsi1. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 0960-7412 120 1 2024 OsHAK4 functions in retrieving sodium from the phloem at the reproductive stage of rice 76 90 EN Jing Che Institute of Plant Science and Resources, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Shao Fei Wang Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Yue Xia Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Shun Ying Yang Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Yan Hua Su Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Ren Fang Shen Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Jian Feng Ma Institute of Plant Science and Resources, Okayama University Soil salinity significantly limits rice productivity, but it is poorly understood how excess sodium (Na+) is delivered to the grains at the reproductive stage. Here, we functionally characterized OsHAK4, a member of the clade IV HAK/KUP/KT transporter subfamily in rice. OsHAK4 was localized to the plasma membrane and exhibited influx transport activity for Na+, but not for K+. Analysis of organ- and growth stage-dependent expression patterns showed that very low expression levels of OsHAK4 were detected at the vegetative growth stage, but its high expression in uppermost node I, peduncle, and rachis was found at the reproductive stage. Immunostaining indicated OsHAK4 localization in the phloem region of node I, peduncle, and rachis. Knockout of OsHAK4 did not affect the growth and Na+ accumulation at the vegetative stage. However, at the reproductive stage, the hak4 mutants accumulated higher Na+ in the peduncle, rachis, husk, and brown rice compared to the wild-type rice. Element imaging revealed higher Na+ accumulation at the phloem region of the peduncle in the mutants. These results indicate that OsHAK4 plays a crucial role in retrieving Na+ from the phloem in the upper nodes, peduncle, and rachis, thereby preventing Na+ distribution to the grains at the reproductive stage of rice. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 2041-1723 16 1 2025 A node-localized efflux transporter for loading iron to developing tissues in rice 9916 EN Jing Che Institute of Plant Science and Resources, Okayama University Sheng Huang Institute of Plant Science and Resources, Okayama University Yuting Qu State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Yuma Yoshioka Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Chiyuri Tomita Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Takaaki Miyaji Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Zhenyang Liu State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Renfang Shen State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences Naoki Yamaji Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Iron (Fe) is an essential micronutrient for plant growth and development. It plays crucial roles in various organs and tissues of plants, but the molecular mechanisms governing its distribution to the above-ground parts after root uptake remain unclear. In this study, we identify OsIET1 (Oryza sativa Iron Efflux Transporter 1), a rice gene highly expressed in the nodes. OsIET1 encodes a plasma membrane-localized protein, which shows efflux transport activity for ferrous iron. It is predominantly expressed in the xylem regions of diffuse vascular bundles, and its expression is upregulated under high Fe conditions. Disruption of OsIET1 impairs Fe allocation, reducing Fe transport to developing tissues (young leaves and grains), while increasing accumulation in nodes and older leaves. This misdistribution causes chlorosis in young leaves and decreases grain yield, especially under Fe-deficient conditions. Furthermore, we detect excessive Fe deposition around the xylem of diffuse vascular bundles in the nodes. Given the pivotal role of nodes in mineral distribution, our results indicate that OsIET1 mediates inter-vascular Fe transfer by facilitating Fe loading into the xylem of diffuse vascular bundles. This process ensures preferential Fe delivery to developing tissues, thereby promoting optimal plant growth and productivity. No potential conflict of interest relevant to this article was reported.

Proceedings of the National Academy of Sciences Acta Medica Okayama 0027-8424 122 32 2025 Structural insights into a citrate transporter that mediates aluminum tolerance in barley e2501933122 EN Tran Nguyen Thao Degree Program in Interdisciplinary Sciences, Graduate School of Environmental, Life, Natural Science, and Technology, Okayama University Namiki Mitani-Ueno Research Core for Plant Stress Science, Institute of Plant Science and Resources, Okayama University Ryo Urano Division of Superconducting and Functional Materials, Research Institute for Interdisciplinary Science, Okayama University Yasunori Saitoh Degree Program in Interdisciplinary Sciences, Graduate School of Environmental, Life, Natural Science, and Technology, Okayama University Peitong Wang Research Core for Plant Stress Science, Institute of Plant Science and Resources, Okayama University Naoki Yamaji Research Core for Plant Stress Science, Institute of Plant Science and Resources, Okayama University Jian-Ren Shen Degree Program in Interdisciplinary Sciences, Graduate School of Environmental, Life, Natural Science, and Technology, Okayama University Wataru Shinoda Degree Program in Interdisciplinary Sciences, Graduate School of Environmental, Life, Natural Science, and Technology, Okayama University Jian Feng Ma Research Core for Plant Stress Science, Institute of Plant Science and Resources, Okayama University Michihiro Suga Degree Program in Interdisciplinary Sciences, Graduate School of Environmental, Life, Natural Science, and Technology, Okayama University HvAACT1 is a major aluminum (Al)-tolerance gene in barley, encoding a citrate transporter that belongs to the multidrug and toxic compound extrusion (MATE) family. This transporter facilitates citrate secretion from the roots, thereby detoxifying external Al ions�\a major constraint of crop production on acidic soils. In this study, we present the outward-facing crystal structure of HvAACT1, providing insights into a citrate transport mechanism. The putative citrate binding site consists of three basic residues�\K126 in transmembrane helix 2 (TM2), R358 in TM7, and R535 in TM12�\creating substantial positive charges in the C-lobe cavity. Proton coupling for substrate transport may involve two pairs of aspartate residues in the N-lobe cavity, one of which corresponds to the essential Asp pair found in prokaryotic H+-coupled MATE transporters belonging to the DinF subfamily. Structural coupling between proton uptake in the N-lobe and citrate extrusion in the C-lobe can be enabled by an extensive, unique hydrogen-bonding network at the extracellular half of the N-lobe. Mutation-based functional analysis, structural comparisons, molecular dynamics simulation, and phylogenic analysis suggest an evolutionary link between citrate MATE transporters and the DinF MATE subfamily. Our findings provide a solid structural basis for citrate transport by HvAACT1 in barley and contribute to a broader understanding of citrate transporter structures in other plant species. No potential conflict of interest relevant to this article was reported.

Oxford University Press (OUP) Acta Medica Okayama 0022-0957 2025 Dual roles of suberin deposition at the endodermal Casparian strip in manganese uptake of rice 1 11 EN Toshiki Fujii Institute of Plant Science and Resources, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Rice roots are characterized by having two Casparian strips (CSs) at the exodermis and endodermis, where transporters for mineral nutrients are expressed. However, the exact role of the CS in expression of the transporters and subsequent nutrient uptake is poorly understood. Here, we first investigated the role of the CS in manganese (Mn) uptake by using a rice mutant (oscasp1) defective in formation of the endodermal CS. Knockout of OsCASP1 resulted in decreased Mn uptake under limited Mn conditions, but increased Mn uptake at high Mn concentration. Immunostaining revealed that knockout of OsCASP1 did not affect the cell specificity of localization of two transporters (OsNramp5 and OsMTP9) required for Mn uptake, but decreased the protein abundance of these transporters at the endodermis regardless of Mn concentrations tested. Furthermore, we found that overaccumulation of suberin at the endodermis of the mutants suppressed the expression of two transporters; the expression of the two transporters was only observed in the endodermal cells without suberin deposition, but not in the cells with suberin deposition. Taken together, our results indicate that there are two roles for the CS in Mn uptake; maintaining normal expression of the transporters at limited Mn concentration and preventing Mn diffusion to the stele at high Mn concentration. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 2041-1723 15 1 2024 Shoot-Silicon-Signal protein to regulate root silicon uptake in rice 10712 EN Naoki Yamaji Institute of Plant Science and Resources, Okayama University Namiki Mitani-Ueno Institute of Plant Science and Resources, Okayama University Toshiki Fujii Institute of Plant Science and Resources, Okayama University Tomonori Shinya Institute of Plant Science and Resources, Okayama University Ji Feng Shao State Key Laboratory of Subtropical Silviculture, Zhejiang Agriculture & Forestry University Shota Watanuki Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yasunori Saitoh Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Plants accumulate silicon to protect them from biotic and abiotic stresses. Especially in rice (Oryza sativa), a typical Si-accumulator, tremendous Si accumulation is indispensable for healthy growth and productivity. Here, we report a shoot-expressed signaling protein, Shoot-Silicon-Signal (SSS), an exceptional homolog of the flowering hormone �gflorigen�h differentiated in Poaceae. SSS transcript is only detected in the shoot, whereas the SSS protein is also detected in the root and phloem sap. When Si is supplied from the root, the SSS transcript rapidly decreases, and then the SSS protein disappears. In sss mutants, root Si uptake and expression of Si transporters are decreased to a basal level regardless of the Si supply. The grain yield of the mutants is decreased to 1/3 due to insufficient Si accumulation. Thus, SSS is a key phloem-mobile protein for integrating root Si uptake and shoot Si accumulation underlying the terrestrial adaptation strategy of grasses. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2045-2322 14 1 2024 Genetic background influences mineral accumulation in rice straw and grains under different soil pH conditions 15139 EN Toshio Yamamoto Institute of Plant Science and Resources, Okayama University Kazunari Kashihara Institute of Plant Science and Resources, Okayama University Tomoyuki Furuta Institute of Plant Science and Resources, Okayama University Qian Zhang Institute of Plant Science and Resources, Okayama University En Yu Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Mineral element accumulation in plants is influenced by soil conditions and varietal factors. We investigated the dynamic accumulation of 12 elements in straw at the flowering stage and in grains at the mature stage in eight rice varieties with different genetic backgrounds (Japonica, Indica, and admixture) and flowering times (early, middle, and late) grown in soil with various pH levels. In straw, Cd, As, Mn, Zn, Ca, Mg, and Cu accumulation was influenced by both soil pH and varietal factors, whereas P, Mo, and K accumulation was influenced by pH, and Fe and Ni accumulation was affected by varietal factors. In grains, Cd, As, Mn, Cu, Ni, Mo, Ca, and Mg accumulation was influenced by both pH and varietal factors, whereas Zn, Fe, and P accumulation was affected by varietal factors, and K accumulation was not altered. Only As, Mn, Ca and Mg showed similar trends in the straw and grains, whereas the pH responses of Zn, P, K, and Ni differed between them. pH and flowering time had synergistic effects on Cd, Zn, and Mn in straw and on Cd, Ni, Mo, and Mn in grains. Soil pH is a major factor influencing mineral uptake in rice straw and grains, and genetic factors, flowering stage factors, and their interaction with soil pH contribute in a combined manner. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2041-1723 12 1 2021 Structural basis for high selectivity of a rice silicon channel Lsi1 6236 EN Yasunori Saitoh Research Institute for Interdisciplinary Science, Okayama University Namiki Mitani-Ueno Institute of Plant Science and Resources, Okayama University Keisuke Saito Research Center for Advanced Science and Technology, The University of Tokyo Kengo Matsuki Graduate School of Natural Science and Technology, Okayama University Sheng Huang Institute of Plant Science and Resources, Okayama University Lingli Yang Research Institute for Interdisciplinary Science, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Hiroshi Ishikita Research Center for Advanced Science and Technology, The University of Tokyo Jian-Ren Shen Research Institute for Interdisciplinary Science, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Silicon (Si), the most abundant mineral element in the earth�fs 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. No potential conflict of interest relevant to this article was reported.

Elsevier Ltd. Acta Medica Okayama 07335210 101 2021 Germplasm evaluation for crop improvement: Analysis of grain quality and cadmium accumulation in barley 103297 EN Kazuhiro Sato Institute of Plant Science and Resources, Okayama University Kazuyoshi Takeda Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Evaluating genetic variation in barley (Hordeum vulgare) germplasm, combined with genome-wide genotyping, is vital for identifying genes controlling important grain-quality traits. For example, in addition to traditional grain quality properties such as starch and protein contents, grain safety parameters such as heavy metal content, are important in the use of barley for human food and animal feed. A number of genes affecting grain quality have been identified by map-based cloning strategies and functionally analyzed by genetic transformation experiments. Moreover, germplasm evaluation yielded information that enabled the introgression of a key gene controlling grain cadmium accumulation into an elite barley cultivar, reducing the content of this heavy metal in grain. Genotyping of molecular markers and resequencing of germplasm accessions may provide information about how grain quality–related loci evolved and how the current allelic diversity was established. In this review, we describe germplasm resources for barley grain quality–related traits and the methods used to analyze the functions of genes controlling these traits, illustrating cadmium accumulation as an example. We also discuss future directions for the efficient identification of grain quality–related genes. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0269-7491 269 2020 Cadmium transfer in contaminated soil-rice systems: Insights from solid-state speciation analysis and stable isotope fractionation 115934 EN Matthias Wiggenhauser Univ. Grenoble Alpes Anne-Marie Aucour Université de Lyon Sarah Bureau Univ. Grenoble Alpes Sylvain Campillo Univ. Grenoble Alpes Philippe Telouk Université de Lyon Marco Romani Centro Ricerche sul Riso, Ente Nazionale Risi, Strada per Ceretto Jian Feng Ma nstitute of Plant Science and Resources, Okayama University Gautier Landrot Synchrotron SOLEIL, L�fOrmes des Merisiers Géraldine Sarret Univ. Grenoble Alpes Initial Cadmium (Cd) isotope fractionation studies in cereals ascribed the retention of Cd and its light isotopes to the binding of Cd to sulfur (S). To better understand the relation of Cd binding to S and Cd isotope fractionation in soils and plants, we combined isotope and XAS speciation analyses in soil-rice systems that were rich in Cd and S. The systems included distinct water management (flooded vs. non-flooded) and rice accessions with (excluder) and without (non-excluder) functional membrane transporter OsHMA3 that transports Cd into root vacuoles. Initially, 13% of Cd in the soil was bound to S. Through soil flooding, the proportion of Cd bound to S increased to 100%. Soil flooding enriched the rice plants towards heavy isotopes (��114/110Cd = �|0.37 to �|0.39%) compared to the plants that grew on non-flooded soils (��114/110Cd = �|0.45 to �|0.56%) suggesting that preferentially light Cd isotopes precipitated into Cd sulfides. Isotope compositions in CaCl2 root extracts indicated that the root surface contributed to the isotope shift between soil and plant during soil flooding. In rice roots, Cd was fully bound to S in all treatments. The roots in the excluder rice strongly retained Cd and its lights isotopes while heavy isotopes were transported to the shoots (��114/110Cdshoot-root 0.16–0.19��). The non-excluder rice accumulated Cd in shoots and the apparent difference in isotope composition between roots and shoots was smaller than that of the excluder rice (��114/110Cdshoot-root �|0.02 to 0.08��). We ascribe the retention of light Cd isotopes in the roots of the excluder rice to the membrane transport of Cd by OsHMA3 and/or chelating Cd–S complexes in the vacuole. Cd–S was the major binding form in flooded soils and rice roots and partly contributed to the immobilization of Cd and its light isotopes in soil-rice systems. No potential conflict of interest relevant to this article was reported.

Oxford University Press Acta Medica Okayama 0022-0957 70 10 2019 The tonoplast-localized transporter OsHMA3 plays an important role in maintaining Zn homeostasis in rice 2717 2725 EN Hongmei Cai Institute of Plant Science and Resources, Okayama University Sheng Huang Institute of Plant Science and Resources, Okayama University Jing Che Institute of Plant Science and Resources, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University In order to respond to fluctuating zinc (Zn) in the environment, plants must have a system to control Zn homeostasis. However, how plants maintain an appropriate level of Zn during their growth and development is still poorly understood. In this study, we found that OsHMA3, a tonoplast-localized transporter for Zn/Cd, plays an important role in Zn homeostasis in rice. Accessions with the functional allele of OsHMA3 showed greater tolerance to high Zn than those with the non-functional allele based on root elongation test. A 67Zn-labeling experiment showed that accessions with loss of function of OsHMA3 had lower Zn accumulation in the roots but similar concentrations in the shoots compared with functional OsHMA3 accessions. When exposed to Zn-free growing medium, the concentration in the root cell sap was rapidly decreased in accessions with functional OsHMA3, but less dramatic changes were observed in non-functional accessions. A mobility experiment showed that more Zn in the roots was translocated to the shoots in accessions with functional OsHMA3. Higher expression levels of OsZIP4, OsZIP5, OsZIP8, and OsZIP10 were found in the roots of accessions with functional OsHMA3 in response to Zn deficiency. Taken together, our results indicate that OsHMA3 plays an important role in rice roots in both Zn detoxification and storage by sequestration into the vacuoles, depending on Zn concentration in the environment. No potential conflict of interest relevant to this article was reported.

Nature Publishing Group Acta Medica Okayama 2041-1723 7 2016 A heavy metal P-type ATPase OsHMA4 prevents copper accumulation in rice grain 12138 EN Xin-Yuan Huang Institute of Biological and Environmental Sciences, University of Aberdeen Fenglin Deng Institute of Plant Science and Resources, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Shannon R.M. Pinson USDA-ARS Dale Bumpers National Rice Research Center Miho Fujii-Kashino Institute of Plant Science and Resources, Okayama University John Danku Institute of Biological and Environmental Sciences, University of Aberdeen Alex Douglas Mary Lou Guerinot Department of Biological Sciences, Dartmouth College David E. Salt Institute of Biological and Environmental Sciences, University of Aberdeen Jian Feng Ma Institute of Plant Science and Resources, Okayama University Rice is a major source of calories and mineral nutrients for over half the world's human population. However, little is known in rice about the genetic basis of variation in accumulation of copper (Cu), an essential but potentially toxic nutrient. Here we identify OsHMA4 as the likely causal gene of a quantitative trait locus controlling Cu accumulation in rice grain. We provide evidence that OsHMA4 functions to sequester Cu into root vacuoles, limiting Cu accumulation in the grain. The difference in grain Cu accumulation is most likely attributed to a single amino acid substitution that leads to different OsHMA4 transport activity. The allele associated with low grain Cu was found in 67 of the 1,367 rice accessions investigated. Identification of natural allelic variation in OsHMA4 may facilitate the development of rice varieties with grain Cu concentrations tuned to both the concentration of Cu in the soil and dietary needs. No potential conflict of interest relevant to this article was reported.

Nature Publishing Group Acta Medica Okayama 2041-1723 6 2015 AtPHT4;4 is a chloroplast-localized ascorbate transporter in Arabidopsis EN Takaaki Miyaji Takashi Kuromori Yu Takeuchi Naoki Yamaji Kengo Yokosho Atsushi Shimazawa Eriko Sugimoto Hiroshi Omote Jian Feng Ma Kazuo Shinozaki Yoshinori Moriyama Ascorbate is an antioxidant and coenzyme for various metabolic reactions in vivo. In plant chloroplasts, high ascorbate levels are required to overcome photoinhibition caused by strong light. However, ascorbate is synthesized in the mitochondria and the molecular mechanisms underlying ascorbate transport into chloroplasts are unknown. Here we show that AtPHT4;4, a member of the phosphate transporter 4 family of Arabidopsis thaliana, functions as an ascorbate transporter. In vitro analysis shows that proteoliposomes containing the purified AtPHT4;4 protein exhibit membrane potential- and Cl-dependent ascorbate uptake. The AtPHT4;4 protein is abundantly expressed in the chloroplast envelope membrane. Knockout of AtPHT4;4 results in decreased levels of the reduced form of ascorbate in the leaves and the heat dissipation process of excessive energy during photosynthesis is compromised. Taken together, these observations indicate that the AtPHT4;4 protein is an ascorbate transporter at the chloroplast envelope membrane, which may be required for tolerance to strong light stress. No potential conflict of interest relevant to this article was reported.