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 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.
(© 2017 American Society of Plant Biologists. All rights reserved.)