The inward-rectifying K+ channel SsAKT1 is a candidate involved in K+ uptake in the halophyte Suaeda salsa under saline condition

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The Shaker AKT1-like channels are considered to be involved in both high- and low-affinity K+ uptake and correlated with salt tolerance in glycophytes. Suaeda salsa (Suaeda maritima subsp. salsa), as a typical salt-accumulating halophyte, is able to absorb K+ efficiently while growing under saline conditions and taking in a large amount of Na+, thus maintaining the K+ concentration in its cells. In this study, the possible functions of the inward-rectifying K+ channel SsAKT1 in K+ uptake and salt tolerance in the halophyte S. salsa were investigated. SsAKT1 from S. salsa was isolated by RT-PCR and characterized using yeast complementation; the responses of SsAKT1 to various KCl and NaCl treatments were investigated by real-time quantitative PCR. SsAKT1 consisted of 879 amino acid residues and shared high homology (60–67 %) with the identified inward-rectifying K+ channels AKT1 from other plants. The expression of SsAKT1 rescued the K+-uptake-defective phenotype of yeast strain CY162, and also suppressed the salt-sensitive phenotype of yeast strain G19, suggesting SsAKT1 functioned as an inward-rectifying K+ channel. SsAKT1 was predominantly expressed in roots, and was induced significantly by K+ starvation; transcript levels increased further on resupply of K+ (0.1–10 mM for 6 h) by 62 % in 0.1 mM K+ and 144–174 % in higher K+ concentrations (1–10 mM). Interestingly, the expression level of SsAKT1 in roots was also induced significantly by short-term treatment (6 h) with NaCl concentrations (25–250 mM). These results demonstrate that the inward-rectifying K+ channel SsAKT1 might mediate both high- and low-affinity K+ uptake in S. salsa, but play a greater role in the low-affinity system. Furthermore, SsAKT1 might also be involved in salt tolerance by participating in the maintenance of K+ nutrition in S. salsa under salinity.