Rice shaker potassium channel OsAKT2 positively regulates salt tolerance and grain yield by mediating K+ redistribution

Maintaining Na⁺ /K⁺ homeostasis is a critical feature for plant survival under salt stress, which depends on the operation of Na⁺ and K⁺ transporters. Although some K⁺ transporters mediating root K⁺ uptake have been reported to be essential to the maintenance of Na⁺ /K⁺ homeostasis, the effect of K⁺ long-distance translocation via phloem on plant salt tolerance remains unclear. Here, we provide physiological and genetic evidence of the involvement of phloem-localized OsAKT2 in rice salt tolerance. OsAKT2 is a K⁺ channel permeable to K⁺ but not to Na⁺ . Under salt stress, a T-DNA knock-out mutant, osakt2 and two CRISPR lines showed a more sensitive phenotype and higher Na⁺ accumulation than wild type. They also contained more K⁺ in shoots but less K⁺ in roots, showing higher Na⁺ /K⁺ ratios. Disruption of OsAKT2 decreases K⁺ concentration in phloem sap and inhibits shoot-to-root redistribution of K⁺ . In addition, OsAKT2 also regulates the translocation of K⁺ and sucrose from old leaves to young leaves, and affects grain shape and yield. These results indicate that OsAKT2-mediated K⁺ redistribution from shoots to roots contributes to maintenance of Na⁺ /K⁺ homeostasis and inhibition of root Na⁺ uptake, providing novel insights into the roles of K⁺ transporters in plant salt tolerance.