title: An aluminum-activated citrate transporter in barley.
abstract: 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.
authors.affiliation: Research Institute for Bioresources, Okayama University, Chuo, Kurashiki, Okayama, 710-0046, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Furukawa
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamaji
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.forename: Namiki
authors.initials: N
authors.lastname: Mitani
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Murata
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sato
authors.forename: Maki
authors.initials: M
authors.lastname: Katsuhara
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Takeda
authors.forename: Jian Feng
authors.initials: JF
authors.lastname: Ma
mesh_terms: D000535:Aluminum / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019343:Citric Acid / Q000378:metabolism; D003001:Cloning, Molecular; D005260:Female; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D001467:Hordeum / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D008293:Malates / Q000378:metabolism; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D019697:Onions / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D008293:Malates; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C020723:citrate-binding transport protein; D049452:Green Fluorescent Proteins; D019343:Citric Acid; C030298:malic acid; D000535:Aluminum; C455846:aluminum citrate