Rice potassium transporter OsHAK18 mediates phloem K⁺ loading and redistribution

Abstract

SUMMARYHigh‐affinity K+ transporters/K+ uptake permeases/K+ transporters (HAK/KUP/KT) are important pathways mediating K+ transport across cell membranes, 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 crucial roles in root K+ uptake and root‐to‐shoot translocation. However, whether HAK/KUP/KT transporters also function in phloem K+ translocation remain unclear. In this study, we revealed that a phloem‐localized rice HAK/KUP/KT transporter, OsHAK18, mediated cell K+ uptake when expressed in yeast, Escherichia coli and Arabidopsis. It was localized at the plasma membrane. Disruption of OsHAK18 rendered rice seedlings insensitive to low‐K+ (LK) stress. After LK stress, some WT leaves showed severe wilting and chlorosis, whereas the corresponding leaves of oshak18 mutant lines (a Tos17 insertion line and two CRISPR lines) remained green and unwilted. Compared with WT, the oshak18 mutants accumulated more K+ in shoots but less K+ in roots after LK stress, leading to a higher shoot/root ratio of K+ per plant. Disruption of OsHAK18 does not affect root K+ uptake and K+ level in xylem sap, but it significantly decreases phloem K+ concentration and inhibits root‐to‐shoot‐to‐root K+ (Rb+) translocation in split‐root assay. These results reveal that OsHAK18 mediates phloem K+ loading and redistribution, whose disruption is in favor of shoot K+ retention under LK stress. Our findings expand the understanding of HAK/KUP/KT transporters' functions and provide a promising strategy for improving rice tolerance to K+ deficiency.

Potassium transporter OsHAK9 regulates seed germination under salt stress by preventing gibberellin degradation through mediating OsGA2ox7 in rice

“…Potassium (K) is an essential macronutrient that plays crucial roles in biochemical and physiological processes underlying plant growth and development (Maathuis and Amtmann, 1999;Shabala and Cuin, 2008;Zörb et al, 2014;Shen et al, 2023). Potassium retention under saline conditions is instrumental in conferring salt tissue tolerance (Shabala and Pottosin, 2014;Wu et al, 2018;Zhao et al, 2020), and enhancing K absorption and maintaining a high K + /Na + ratio constitute a key strategy for plants to withstand salt stress (Véry and Sentenac, 2003;Zhu, 2003;Shabala and Cuin, 2008).…”