An aluminum-activated citrate transporter in barley

Jun Furukawa, Naoki Yamaji, Hua Wang, Namiki Mitani, Yoshiko Murata, Kazuhiro Sato, Maki Katsuhara, Kazuyoshi Takeda, Jian Feng Ma

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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 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.

Original languageEnglish
Pages (from-to)1081-1091
Number of pages11
JournalPlant and Cell Physiology
Volume48
Issue number8
DOIs
Publication statusPublished - Aug 1 2007

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Keywords

  • Aluminum
  • Barley
  • Citrate transporter
  • MATE
  • Resistance
  • Root

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology

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