ZxAKT1 is essential for K + uptake and K + /Na + homeostasis in the succulent xerophyte Zygophyllum xanthoxylum

Summary The inward‐rectifying K + channel AKT 1 constitutes an important pathway for K + acquisition in plant roots. In glycophytes, excessive accumulation of Na + is accompanied by K + deficiency under salt stress. However, in the succulent xerophyte Zygophyllum xanthoxylum , which exhibits excellent adaptability to adverse environments, K + concentration remains at a relatively constant level despite increased levels of Na + under salinity and drought conditions. In this study, the contribution of Zx AKT 1 to maintaining K + and Na + homeostasis in Z. xanthoxylum was investigated. Expression of Zx AKT 1 rescued the K + ‐uptake‐defective phenotype of yeast strain CY 162, suppressed the salt‐sensitive phenotype of yeast strain G19, and complemented the low‐K + ‐sensitive phenotype of Arabidopsis akt1 mutant, indicating that Zx AKT 1 functions as an inward‐rectifying K + channel. Zx AKT 1 was predominantly expressed in roots, and was induced under high concentrations of either KC l or NaCl. By using RNA interference technique, we found that Zx AKT 1 ‐silenced plants exhibited stunted growth compared to wild‐type Z. xanthoxylum . Further experiments showed that Zx AKT 1 ‐silenced plants exhibited a significant decline in net uptake of K + and Na + , resulting in decreased concentrations of K + and Na + , as compared to wild‐type Z. xanthoxylum grown under 50 m m NaCl. Compared with wild‐type, the expression levels of genes encoding several transporters/channels related to K + /Na + homeostasis, including Zx SKOR , Zx NHX , Zx SOS 1 and Zx HKT 1 ; 1 , were reduced in various tissues of a Zx AKT 1 ‐silenced line. These findings suggest that Zx AKT 1 not only plays a crucial role in K + uptake but also functions in modulating Na + uptake and transport systems in Z. xanthoxylum , thereby affecting its normal growth.