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.
Highlights
Potassium represents 2.6% of the weight of the Earth’s crust
Because of the different expression patterns between these genes in H. vulgare and H. brevisubulatum, we focused on functional study of HbHAK1
Our study significantly revealed the natural adaptive sites of HbHAK1 were the key residues for improving HAK1-type activity, highlighting the potential value for crops to promote K+ uptake under stresses
Summary
Potassium represents 2.6% of the weight of the Earth’s crust. dissolved K in soil—as the only fraction directly available to plant—is deficient, especially in saline–alkali land and arid land [1]. As ion fluxes control ion concentration, the HAK/KUP/KT (high affinity K+/K+ uptake proteins/K+ transporter) proteins function as K+-transporters and the major contributor for K+ nutrition in K+ depleted soil [4]. Genes in cluster I are the most functionally revealed, including classical AtHAK5, HvHAK1, OsHAK1, OsHAK5, ThHAK1, SlHAK5, CcHAK1 and so on [6,7,8,9,10,11,12] They all have a high-affinity K+ transport feature that allows plant to thrive under low-K+ (
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