NRT1.5/NPF7.3 Functions as a Proton-Coupled H/K Antiporter for K Loading into the Xylem in Arabidopsis.

Potassium and nitrogen are essential macronutrients for plant growth and have a positive impact on crop yield. Previous studies have indicated that the absorption and translocation of K and NO are correlated with each other in plants; however, the molecular mechanism that coordinates K and NO transport remains unknown. In this study, using a forward genetic approach, we isolated a low-K-sensitive mutant, , that showed a leaf chlorosis phenotype under low-K conditions. encodes the transporter NRT1.5/NPF7.3, a member of the NRT1/PTR (Nitrate Transporter 1/Peptide Transporter) family. The / mutants exhibit a remarkable defect in both K and NO translocation from root to shoot, especially under low-K conditions. This study demonstrates that LKS2 (NRT1.5) functions as a proton-coupled H/K antiporter. Proton gradient can promote NRT1.5-mediated K release out of root parenchyma cells and facilitate K loading into the xylem. This study reveals that NRT1.5 plays a crucial role in K translocation from root to shoot and is also involved in the coordination of K/NO distribution in plants.