Comparative Functional Analysis of Class II Potassium Transporters, SvHKT2;1, SvHKT2;2, and HvHKT2;1, on Ionic Transport and Salt Tolerance in Transgenic Arabidopsis
Yuichi Tada | Aki Ohnuma
Class II high-affinity potassium transporters (HKT2s) mediate Na<sup>+</sup>–K<sup>+</sup> cotransport and Na<sup>+</sup>/K<sup>+</sup> homeostasis under K<sup>+</sup>-starved or saline conditions. Their functions have been studied in yeast and <i>X. laevis</i> oocytes; however, little is known about their respective properties in plant cells. In this study, we characterized the Na<sup>+</sup> and K<sup>+</sup> transport properties of SvHKT2;1, SvHKT2;2 and HvHKT2;1 in Arabidopsis under different ionic conditions. The differences were detected in shoot K<sup>+</sup> accumulation and root K<sup>+</sup> uptake under salt stress conditions, K<sup>+</sup> accumulation in roots and phloem sap under K<sup>+</sup>-starved conditions, and shoot and root Na<sup>+</sup> accumulation under K<sup>+</sup>-starved conditions among the <i>HKT2s</i> transgenic lines and WT plants. These results indicate the diverse ionic transport properties of these HKT2s in plant cells, which could not be detected using yeast or <i>X. laevis</i> oocytes. Furthermore, Arabidopsis expressing <i>HKT2s</i> showed reduced salt tolerance, while over-expression of <i>HvHKT2;1</i> in barley, which has the ability to sequestrate Na<sup>+</sup>, showed enhanced salt tolerance by accumulating Na<sup>+</sup> in the shoots. These results suggest that the coordinated enhancement of Na<sup>+</sup> accumulation and sequestration mechanisms in shoots could be a promising strategy to confer salt tolerance to glycophytes.
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