A Low-Affinity K+ Transporter AlHKT2;1 from Recretohalophyte Aeluropus lagopoides Confers Salt Tolerance in Yeast.

The high-affinity potassium transporters (HKT) are highly important for stress tolerance in plants as they uniquely maintain K(+)/Na(+) ratio for their survival and growth. In this study a novel HKT gene AlHKT2;1 was isolated and characterized from salt secreting halophyte, Aeluropus lagopoides. The AlHKT2;1 cDNA comprised of an open reading frame of 1,581 bp, encoding a protein of 526 amino acid residues. It belongs to class II HKTs and showed high homology with other HKT genes. Functional characterization of AlHKT2;1 in both K(+) uptake-deficient (WΔ6) and Na(+)-sensitive yeast mutants (G19) showed the characteristic feature of low-affinity K(+) transporter supporting the growth at >1 mM KCl concentration. The transformed yeast cells showed high sensitivity to NaCl; however, the addition of KCl along with NaCl support the growth of AlHKT2;1 expressing mutant. Ion content analysis of yeast cells with AlHKT2;1 grown in high NaCl medium supplemented with KCl revealed that salt tolerance was correlated with accumulation of K(+) during salt stress. These results suggest that AlHKT2;1 plays an important role in the K(+) uptake during salt stress and in maintaining a high K(+)/Na(+) ratio in the cytosol.