A putative plasma membrane cation/proton antiporter from soybean confers salt tolerance in Arabidopsis

Cation transport is thought to be an important process for ion homeostasis in plant cells. Here, we report that a soybean putative cation/proton antiporter GmCAX1 may be a mediator of this process. GmCAX1 is expressed in all tissues of the soybean plants but at a lower level in roots. Its expression was induced by PEG, ABA, Ca2+, Na+ and Li+ treatments. The GmCAX1-GFP fusion protein was mainly localized in plasma membrane of the transgenic Arabidopsis plant cells and onion epidermal cells. Transgenic Arabidopsis plants overexpressing GmCAX1 accumulated less Na+, K+, and Li+, and were more tolerant to elevated Li+ and Na+ levels during germination when compared with the controls. These results suggest that GmCAX1 may function as an antiporter for Na+, K+ and Li+. Modulation of this antiporter may be beneficial for regulation of ion homeostasis and thus plant salt tolerance.