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+ uptakeaEurodeficient (W Delta 6) 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.