Identification and Sequence Analysis of Sulfate/Selenate Transporters in Selenium Hyper- and Non-accumulating Astragalus Plant Species

Abstract

Selenium is an essential element for human health, consumed mainly from plant sources. In plants, there is good evidence that selenate is transported via sulfate transporters, and that this anion will interact competitively with sulfate. Some of selenium (Se)-hyper-accumulating plant species belonging to the genus Astragalus are known for their capacity to accumulate up to 0.6% of their foliar dry weight as Se. Comparative analyses of sulfate transporter genes of contrasting Se hyper-accumulator and non-accumulator species will be helpful for a better understanding of sulfate/selenium uptake processes and provide insights on the substrate binding site for the transported anion. The gene family of sulfate transporters is subdivided into five groups with distinct and/or functional characteristics. cDNAs for sulfate transporters belonging to the Group 1, 2, 3 and 4 of the sulfate transporter families were isolated from both Se hyper-accumulating (Astragalus racemosus, Astragalus bisulfcatus, Astragalus crotalariae) and the closely related non-accumulating species (Astragalus glycophyllos, Astragalus drummondii). Sequence analysis was performed to identify sequence variations which may contribute to selectivity of sulfate and selenate uptake and distribution.