title: Characterization of the histidine-rich loop of Arabidopsis vacuolar membrane zinc transporter AtMTP1 as a sensor of zinc level in the cytosol.
abstract: The vacuolar Zn(2+)/H(+) antiporter of Arabidopsis thaliana, AtMTP1, has a long cytosolic histidine-rich loop. A mutated AtMTP1 in which the first half of the loop (His-half) was deleted exhibited a 11-fold higher transport velocity in yeast cells. Transgenic lines overexpressing the His-half-deleted AtMTP1 in the loss-of-function mutant were evaluated for growth and metal content in the presence of various zinc concentrations. These overexpressing lines (35S-AtMTP1 and 35S-His-half lines) showed high tolerance to excess concentrations of zinc at 150 µM, as did the wild type, compared with the loss-of-function line. The His-half AtMTP1 transported cobalt in a heterologous expression assay in yeast, but the cumulative amount of cobalt in 35S-His-half plants was not increased. Moreover, the accumulation of calcium and iron was not changed in plants. Under zinc-deficient conditions, growth of 35S-His-half lines was markedly suppressed. Under the same conditions, the 35S-His-half lines accumulated larger amounts of zinc in roots and smaller amounts of zinc in shoots compared with the other lines, suggesting an abnormal accumulation of zinc in the roots of 35S-His-half lines. As a result, the shoots may exhibit zinc deficiency. Taken together, these results suggest that the His-loop acts as a sensor of cytosolic zinc to maintain an essential level in the cytosol and that the dysfunction of the loop results in an uncontrolled accumulation of zinc in the vacuoles of root cells.
authors.affiliation: Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan.
authors.forename: Natsuki
authors.initials: N
authors.lastname: Tanaka
authors.affiliation: Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujiwara
authors.affiliation: Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Tomioka
authors.affiliation: Department of Plant Physiology, Ruhr-University Bochum, D-44801 Bochum, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Krämer
authors.affiliation: Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan maeshima@agr.nagoya-u.ac.jp mkawachi@agr.nagoya-u.ac.jp.
authors.forename: Miki
authors.initials: M
authors.lastname: Kawachi
authors.affiliation: Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan maeshima@agr.nagoya-u.ac.jp mkawachi@agr.nagoya-u.ac.jp.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Maeshima
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D030821:Plants, Genetically Modified; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism*; D015032:Zinc / Q000172:deficiency / Q000378:metabolism* / Q000494:pharmacology; D000099053:Histidine-Rich Glycoprotein
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D002734:Chlorophyll; D003035:Cobalt; D011506:Proteins; D015032:Zinc; D000099053:Histidine-Rich Glycoprotein; C500829:ZAT protein, Arabidopsis
keywords: Histidine-rich loop; MTP1; Zinc deficiency; Zinc homeostasis; Zinc transporter