SsHKT1;1 is a potassium transporter of the C₃ halophyte Suaeda salsa that is involved in salt tolerance

SsHKT1;1, a HKT1 homologue, was isolated from the C3 halophyte Suaeda salsa L. and its ion transport properties were investigated in heterologous systems. The expression of SsHKT1;1 suppressed a K+ transport-defective phenotype of the yeast strain CY162 (Δtrk1Δtrk2), suggesting the enhancement of K+ uptake with SsHKT1;1. However, it did not suppress the salt-sensitive phenotype of the yeast strain G19 (Δena1-4), which lacks a major component of Na+ efflux. Transgenic Arabidopsis thaliana (L.) Heynh. plants overexpressing SsHKT1;1 showed enhanced salt tolerance and increased shoot K+ concentration, whereas no significant changes in shoot Na+ concentration were observed. S. salsa was also used to investigate K+ uptake properties under salinity. The K+ transporters in the roots selectively mediated K+ uptake irrespective of external Na+ and their inhibitor did not affect Na+ uptake at low K+. Thus, both molecular and physiological studies provide strong in vivo evidence that SsHKT1;1 mainly acts as a potassium transporter in heterologous expression systems and S. salsa, and that it is involved in salt tolerance by taking part in the maintenance of cytosolic cation homeostasis, particularly, in the maintenance of K+ nutrition under salinity.