An aluminum-activated citrate transporter in barley

Plant Cell Physiol. 2007 Aug;48(8):1081-91. doi: 10.1093/pcp/pcm091. Epub 2007 Jul 18.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aluminum / pharmacology*
  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Citric Acid / metabolism
  • Cloning, Molecular
  • Female
  • Gene Expression Regulation, Plant / drug effects
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Hordeum / classification
  • Hordeum / genetics
  • Hordeum / metabolism*
  • In Situ Hybridization
  • Malates / metabolism
  • 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
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sequence Analysis, DNA
  • Xenopus laevis


  • Carrier Proteins
  • Malates
  • Plant Proteins
  • Recombinant Fusion Proteins
  • citrate-binding transport protein
  • Green Fluorescent Proteins
  • Citric Acid
  • malic acid
  • Aluminum
  • aluminum citrate

Associated data

  • GENBANK/AB302223
  • GENBANK/AB331641