The K<sup>+</sup> and NO<sub>3</sub><sup>−</sup> Interaction Mediated by NITRATE TRANSPORTER1.1 Ensures Better Plant Growth under K<sup>+</sup>-Limiting Conditions
Xian Zhi Fang, Xing Xing Liu, Ya Xing Zhu, Jiayuan Ye, Chong Wei Jin
Abstract
K+ and NO3 − are the major forms of potassium and nitrogen that are absorbed by the roots of most terrestrial plants. In this study, we observed that a close relationship between NO3 − and K+ in Arabidopsis (Arabidopsis thaliana) is mediated by NITRATE TRANSPORTER1.1 (NRT1.1). The nrt1.1 knockout mutants showed disturbed K+ uptake and root-to-shoot allocation, and were characterized by growth arrest under K+-limiting conditions. The K+ uptake and root-to-shoot allocation of these mutants were partially recovered by expressing NRT1.1 in the root epidermis-cortex and central vasculature using SULFATE TRANSPORTER1;2 and PHOSPHATE1 promoters, respectively. Two-way analysis of variance based on the K+ contents in nrt1.1-1/K + transporter1, nrt1.1-1/high-affinity K + transporter5-3, nrt1.1-1/K + uptake permease7, and nrt1.1-1/stelar K + outward rectifier-2 double mutants and the corresponding single mutants and wild-type plants revealed physiological interactions between NRT1.1 and K+ channels/transporters located in the root epidermis–cortex and central vasculature. Further study revealed that these K+ uptake-related interactions are dependent on an H+-consuming mechanism associated with the H+/NO3 − symport mediated by NRT1.1. Collectively, these data indicate that patterns of NRT1.1 expression in the root epidermis–cortex and central vasculature are coordinated with K+ channels/transporters to improve K+ uptake and root-to-shoot allocation, respectively, which in turn ensures better growth under K+-limiting conditions.