title: The Phytosiderophore Efflux Transporter TOM2 Is Involved in Metal Transport in Rice.
abstract: Iron is an essential metal element for all living organisms. Graminaceous plants produce and secrete mugineic acid family phytosiderophores from their roots to acquire iron in the soil. Phytosiderophores chelate and solubilize insoluble iron hydroxide in the soil. Subsequently, plants take up iron-phytosiderophore complexes through specific transporters on the root cell membrane. Phytosiderophores are also thought to be important for the internal transport of various transition metals, including iron. In this study, we analyzed TOM2 and TOM3, rice homologs of transporter of mugineic acid family phytosiderophores 1 (TOM1), a crucial efflux transporter directly involved in phytosiderophore secretion into the soil. Transgenic rice analysis using promoter-β-glucuronidase revealed that TOM2 was expressed in tissues involved in metal translocation, whereas TOM3 was expressed only in restricted parts of the plant. Strong TOM2 expression was observed in developing tissues during seed maturation and germination, whereas TOM3 expression was weak during seed maturation. Transgenic rice in which TOM2 expression was repressed by RNA interference showed growth defects compared with non-transformants and TOM3-repressed rice. Xenopus laevis oocytes expressing TOM2 released (14)C-labeled deoxymugineic acid, the initial phytosiderophore compound in the biosynthetic pathway in rice. In onion epidermal and rice root cells, the TOM2-GFP fusion protein localized to the cell membrane, indicating that the TOM2 protein is a transporter for phytosiderophore efflux to the cell exterior. Our results indicate that TOM2 is involved in the internal transport of deoxymugineic acid, which is required for normal plant growth.
authors.affiliation: From the Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nozoye
authors.affiliation: From the Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Nagasaka
authors.affiliation: the Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa 921-8836, Japan, and.
authors.forename: Takanori
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: the Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-7 Aobayama, Sendai 980-8579, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sato
authors.affiliation: the Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-7 Aobayama, Sendai 980-8579, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Uozumi
authors.affiliation: From the Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Nakanishi
authors.affiliation: From the Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 Japan, the Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa 921-8836, Japan, and annaoko@mail.ecc.u-tokyo.ac.jp.
authors.forename: Naoko K
authors.initials: NK
authors.lastname: Nishizawa
mesh_terms: D000818:Animals; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D023061:Gene Order; D017343:Genes, Plant; D007501:Iron / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017262:Siderophores / Q000378:metabolism; D014018:Tissue Distribution; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; D017262:Siderophores; D001383:Azetidinecarboxylic Acid; D007501:Iron; C052863:mugineic acid
keywords: iron; nutrition; plant molecular biology; plant physiology; transporter