Soluble aluminum (Al 3+) is a major constraint to plant growth in highly acidic soils, which comprise up to 50% of the world's arable land. The primary mechanism of Al resistance described in plants is the chelation of Al 3+ cations by release of organic acids into the rhizosphere. Candidate aluminum tolerance genes encoding organic acid transporter of the ALMT (aluminum-activated malate transporter) and MATE (multi-drug and toxic compound extrusion) families have been characterized in several plant species. In this study, we have isolated in five different cultivars the rye ScAACT1 gene, homolog to barley aluminum activated citrate transporter HvAACT1. This gene mapped to the 7RS chromosome arm, 25 cM away from the ScALMT1 aluminum tolerance gene. The gene consisted of 13 exons and 12 introns and encodes a predicted membrane protein that contains the MatE domain and at least seven putative transmembrane regions. Expression of the ScAACT1 gene is Al-induced, but there were differences in the levels of expression among the cultivars analyzed. A new quantitative trait locus for Al tolerance in rye that co-localizes with the ScAACT1 gene was detected in the 7RS chromosome arm. These results suggest that the ScAACT1 gene is a candidate gene for increased Al tolerance in rye. The phylogenetic relationships between different MATE proteins are discussed.
