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.

Automated summary

The study demonstrates the important role of OsAKT2 in rice salt tolerance through phloem-mediated K+ redistribution, elucidating its mechanism in maintaining Na+/K+ homeostasis by regulating K+ redistribution and affecting root Na+ uptake. This provides new insights into the roles of K+ transporters in plant salt tolerance.