An aluminum-activated citrate transporter in barley [Hordeum vulgare]

• Published in: Plant and cell physiology 2007-08, Vol.48 (8), p.1081-1091
• Main Authors: Furukawa, J.(Okayama Univ., Kurashiki (Japan). Research Inst. for Bioresources), Yamaji, N, Wang, H, Mitani, N, Murata, Y, Sato, K, Katsuhara, M, Takeda, K, Ma, J.F
• Format: Article
• Language: English
• Subjects: ALUMINIO; ALUMINIUM; Aluminum; Aluminum - pharmacology; Animals; Barley; Carrier Proteins - genetics; Carrier Proteins - metabolism; Carrier Proteins - physiology; CITRATE; Citrate transporter; CITRATES; CITRATOS; Citric Acid - metabolism; CLONACION; CLONAGE; CLONING; Cloning, Molecular; EXPRESION GENICA; EXPRESSION DES GENES; Female; GENE; GENE EXPRESSION; Gene Expression Regulation, Plant - drug effects; GENES; GENETICA CUANTITATIVA; GENETIQUE QUANTITATIVE; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Hordeum - classification; Hordeum - genetics; Hordeum - metabolism; HORDEUM VULGARE; IDENTIFICACION; IDENTIFICATION; In Situ Hybridization; Malates - metabolism; MATE; Membrane Potentials - genetics; Membrane Potentials - physiology; Molecular Sequence Data; Nicotiana - genetics; Nicotiana - metabolism; Oligonucleotide Array Sequence Analysis; Onions - genetics; Onions - metabolism; Phylogeny; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Proteins - physiology; Plant Roots - genetics; Plant Roots - metabolism; Plants, Genetically Modified; QUANTITATIVE GENETICS; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Resistance; RESISTANCE AUX FACTEURS NUISIBLES; RESISTANCE TO INJURIOUS FACTOR; RESISTENCIA A AGENTES DANINOS; Root; Sequence Analysis, DNA; Xenopus laevis
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcm091

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 14C-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.