The outward Shaker channel OsK5.2 is beneficial to the plant salt tolerance through its role in K+ translocation and its control of leaf transpiration

High soil salinity constitutes a major environmental constraint to crop production worldwide, and the identification of genetic determinants of plant salt tolerance is awaited by breeders. While the leaf K+ to Na+ homeostasis is considered as key parameter of plant salt tolerance, the underlying mechanisms are not fully identified. Especially, the contribution of K+ channels to this homeostasis has been scarcely examined. Here, we show, using a reverse genetics approach, that the outwardly-rectifying K+ channel OsK5.2, involved in K+ translocation to the shoot and K+ release by guard cells for stomatal closure, is a strong determinant of rice salt tolerance. Upon saline treatment, OsK5.2 function in xylem sap K+ load was maintained, and even transiently increased, in roots. OsK5.2 selectively handled K+ in roots and was not involved in xylem sap Na+ load. In shoots, OsK5.2 expression was up-regulated from the onset of the saline treatment, enabling fast reduction of stomatal aperture, decreased transpirational water flow and therefore decreased trans-plant Na+ flux and reduced leaf Na+ accumulation. Thus, the OsK5.2 functions allowed shoot K+ nutrition while minimizing arrival of Na+, and appeared highly beneficial to the leaf K+ to Na+ homeostasis, the avoidance of salt toxicity and plant growth maintaining.