Abstract
Potassium retention under saline conditions has emerged as an important determinant for salt tolerance in plants. Halophytic Hordeum brevisubulatum evolves better strategies to retain K(+) to improve high-salt tolerance. Hence, uncovering K(+)-efficient uptake under salt stress is vital for understanding K(+) homeostasis. HAK/KUP/KT transporters play important roles in promoting K(+) uptake during multiple stresses. Here, we obtained nine salt-induced HAK/KUP/KT members in H. brevisubulatum with different expression patterns compared with H. vulgare through transcriptomic analysis. One member HbHAK1 showed high-affinity K(+) transporter activity in athak5 to cope with low-K(+) or salt stresses. The expression of HbHAK1 in yeast Cy162 strains exhibited strong activities in K(+) uptake under extremely low external K(+) conditions and reducing Na(+) toxicity to maintain the survival of yeast cells under high-salt-stress. Comparing with the sequence of barley HvHAK1, we found that C170 and R342 in a conserved domain played pivotal roles in K(+) selectivity under extremely low-K(+) conditions (10 μM) and that A13 was responsible for the salt tolerance. Our findings revealed the mechanism of HbHAK1 for K(+) accumulation and the significant natural adaptive sites for HAK1 activity, highlighting the potential value for crops to promote K(+)-uptake under stresses.