Functional characterization of two half-size ABC transporter genes in aluminium-accumulating buckwheat

Buckwheat (Fagopyrum esculentum Moench) is able to detoxify high aluminium (Al) internally by sequestering it to the vacuoles in the leaves; however, the molecular mechanisms underlying this sequestration are unknown. We performed proteomic analysis with the leaf tonoplast-rich fraction and identified two half-size ABC transporters; FeASL1.1 and FeALS1.2. We investigated the gene expression patterns and subcellular localization. To demonstrate their physiological role, we expressed FeALS1.1 or FeALS1.2 in the Arabidopsis atals1 mutant under the control of AtALS1 promoter. FeALS1.1 expression was upregulated by Al in both the leaves and the roots, and its expression level in the roots was six times higher than its homologous gene (AtALS1) of Arabidopsis. FeALS1.2 expression, however, was not affected by Al but showed a 39 times higher expression level than AtALS1 in the leaves. When FeALS1.1 or FeALS1.2 was expressed in atals1, both of them recovered their Al tolerance through altering the subcellular localization of Al in root cells. Taken together, our results indicate that FeALS1.1 and FeALS1.2 are involved in the internal detoxification of Al in the roots and leaves, respectively, by sequestering Al into the vacuoles. Their high expression is probably required for high Al tolerance in buckwheat.