A wheat gene encoding an aluminum‐activated malate transporter

Abstract

SummaryThe major constraint to plant growth in acid soils is the presence of toxic aluminum (Al) cations, which inhibit root elongation. The enhanced Al tolerance exhibited by some cultivars of wheat is associated with the Al-dependent ef¯ux of malate from root apices. Malate forms a stable complex with Al that is harmless to plants and, therefore, this ef¯ux of malate forms the basis of a hypothesis to explain Al tolerance in wheat. Here, we report on the cloning of a wheat gene, ALMT1 (aluminum-activated malate transporter), that co-segregates with Al tolerance in F 2 and F 3 populations derived from crosses between near-isogenic wheat lines that differ in Al tolerance. The ALMT1 gene encodes a membrane protein, which is constitutively expressed in the root apices of the Al-tolerant line at greater levels than in the near-isogenic but Alsensitive line. Heterologous expression of ALMT1 in Xenopus oocytes, rice and cultured tobacco cells conferred an Al-activated malate ef¯ux. Additionally, ALMT1 increased the tolerance of tobacco cells to Al treatment. These ®ndings demonstrate that ALMT1 encodes an Al-activated malate transporter that is capable of conferring Al tolerance to plant cells.

The roles of organic anion permeases in aluminium resistance and mineral nutrition

“…The two alleles of the TaALMT1 coding region that have been identified differ by six nucleotides with only two of these differences encoding for different amino acids in the predicted proteins [6]. The alleles occur in both Al 3+ -resistant and Al 3+ -sensitive wheat genotypes indicating that the different amino acids do not confer differences in resistance.…”

“…Oocytes expressing the BnALMT genes generate larger currents than oocytes expressing either TaALMT1 or AtALMT1 but this may reflect experimental differences (e.g. amount of cRNA injected) rather than protein function because when expressed in tobacco suspension cells, the wheat and B. napus genes generate similar phenotypes [6,19]. For example, Al 3+ -activated malate efflux in tobacco cells for both genes is about 0.5 lmole/g fresh weight/hour.…”

“…In addition to their value as tools for the genetic modification of plants, the Al 3+ resistance genes can be used as markers in breeding plants better suited to acid soils. For instance, regions of the coding, intron and promoter of TaALMT1 have been used as markers for Al 3+ resistance in wheat [6,14,44]. To date all of the organic anion transport proteins involved in Al 3+ resistance require Al 3+ for activation which limits their application for other purposes such as improving the P nutrition of plants.…”

Genetic Opportunities to Improve Cereal Root Systems for Dryland Agriculture

“…Wheat is generally sensitive to acid soils; elegant work in both Japan and Australia (Delhaize et al, 1993;Delhaize and Ryan, 1995;Matsumoto, 2000;Ma et al, 2001;Osawa and Matsumoto, 2001;Sasaki et al, 2004) has been responsible for identifying the mechanism for acid soil tolerance in wheat and the gene responsible. No adverse effects of this gene in different genetic backgrounds have been detected.…”

Characterisation of genetic variation for aluminium resistance and polyphenol oxidase activity in genebank accessions of spelt wheat

“…However, a major locus located on the long arm of chromosome 4D (4DL) controls Al resistance via malate efflux in genetically diverse wheat germplasm (Riede and Anderson 1996, Milla and Gustafson 2001, Raman et al 2005a. The usefulness of molecular markers especially that are linked with the wheat Al-resistance gene TaALMT1 (Sasaki et al 2004, Raman et al 2005a, 2006a can be tested to select Al-resistant spelt genotypes for cultivation on acidic soils.…”