Rice potassium transporter OsHAK18 mediates phloem K+loading and redistribution

Abstract

ABSTRACTHigh-Affinity K+transporters/K+Uptake Permeases/K+Transporters (HAK/KUP/KT) are important pathways mediating K+transport across cell membrane, which function in maintaining K+homeostasis during plant growth and stress response. An increasing number of studies have shown that HAK/KUP/KT transporters play important roles in potassium uptake and root-to-shoot translocation. However, whether some HAK/KUP/KT transporters mediate K+redistribution in phloem remains unknown. In this study, we revealed that a phloem-localized HAK/KUP/KT transporter, OsHAK18 operated as a typical KUP/HAK/KT transporter mediating cell K+uptake when expressed in yeast,E. coliandArabidopsis. It was localized at plasma membrane. Disruption ofOsHAK18rendered rice seedlings insensitive to low-K+stress. Compared with WT, theoshak18mutants accumulated more K+in shoots but less K+in roots, leading to a higher shoot/root ratio of K+per plant. Although disruption ofOsHAK18doesn’t affect root K+uptake and K+level in xylem sap, it significantly decreases phloem K+concentration and inhibits root-to-shoot-to-root K+translocation in split-root assay. These results reveal that OsHAK18 mediates phloem K+loading and redistribution, whose disruption is favor of shoot K+retention under low-K+stress. Our findings not only reveal a unique function of rice HAK/KUP/KT family member, but also provide a promising strategy to improve rice tolerance under K+deficiency.