Abstract
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(3)(-) are correlated with each other in plants; however, the molecular mechanism that coordinates K(+) and NO(3)(-) transport remains unknown. In this study, using a forward genetic approach, we isolated a low-K(+)-sensitive Arabidopsis thaliana mutant, lks2, that showed a leaf chlorosis phenotype under low-K(+) conditions. LKS2 encodes the transporter NRT1.5/NPF7.3, a member of the NRT1/PTR (Nitrate Transporter 1/Peptide Transporter) family. The lks2/nrt1.5 mutants exhibit a remarkable defect in both K(+) and NO(3)(-) 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(3)(-) distribution in plants.