Potassium Transporter KUP7 Is Involved in K+ Acquisition and Translocation in Arabidopsis Root under K+-Limited Conditions

Potassium (K+) is one of the essential macronutrients for plant growth and development. K+ uptake from environment and K+ translocation in plants are conducted by K+ channels and transporters. In this study, we demonstrated that KT/HAK/KUP transporter KUP7 plays crucial roles in K+ uptake and translocation in Arabidopsis root. The kup7 mutant exhibited a sensitive phenotype on low-K+ medium, whose leaves showed chlorosis symptoms compared with wild-type plants. Loss of function of KUP7 led to a reduction of K+ uptake rate and K+ content in xylem sap under K+-deficient conditions. Thus, the K+ content in kup7 shoot was significantly reduced under low-K+ conditions. Localization analysis revealed that KUP7 was predominantly targeted to the plasma membrane. The complementation assay in yeast suggested that KUP7 could mediate K+ transport. In addition, phosphorylation on S80, S719, and S721 was important for KUP7 activity. KUP7 was ubiquitously expressed in many organs/ tissues, and showed a higher expression level in Arabidopsis root. Together, our data demonstrated that KUP7 is crucial for K+ uptake in Arabidopsis root and might be also involved in K+ transport into xylem sap, affecting K+ translocation from root toward shoot, especially under K+-limited conditions.