Expression of the AKT1-type K⁺ channel gene from Puccinellia tenuiflora, PutAKT1, enhances salt tolerance in Arabidopsis

Potassium channels are important for many physiological functions in plants, one of which is to regulate plant adaptation to stress conditions. In this study, a K⁺ channel PutAKT1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. A phylogenetic analysis showed that PutAKT1 belongs to the AKT1-subfamily in the Shaker K⁺ channel family. PutAKT1 was localized in the plasma membrane and it was preferentially expressed in the roots. The expression of PutAKT1 was induced by K⁺-starvation stress in the roots and was not down-regulated by the presence of excess Na⁺. Arabidopsis plants over-expressing PutAKT1 showed enhanced salt tolerance compared to wild-type plants as shown by their shoot phenotype and dry weight. Expression of PutAKT1 increased the K⁺ content of Arabidopsis under normal, K⁺-starvation, and NaCl-stress conditions. Arabidopsis expressing PutAKT1 also showed a decrease in Na⁺ accumulation both in the shoot and in the root. These results suggest that PutAKT1 is involved in mediating K⁺ uptake (i) both in low- and in high-affinity K⁺ uptake range, and (ii) unlike its homologs in rice, even under salt-stress condition.