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Potassium and nitrogen are essential macronutrients for plant growth and crop yields.Although the previous studies have indicated that the absorption and translocation of K+ and NO3-are correlated each other,the molecular mechanism for the coordination between K+ and NO3-transport remains unknown.In this study,using a forward genetic approach,we isolated a low-K+-sensitive Arabidopsis mutant Iks2 that exhibits a defect in K+ translocation from root to shoot.Under low-K+ conditions,the K+ contents in Iks2shoot were reduced,while the K+ contents in Iks2 root were significantly increased compared with wild-type plants.Map-based cloning revealed that LKS2 encodes the nitrate transporter NRT1.5/NPF7.3,a member of the NRT1/PTR family.Similar to K+,the NO3-translocation from root to shoot was also impaired in Iks2 mutant.It is suggested that NRT1.5 not only participates in NO3-translocation but also regulates K+ transport from root to shoot.Using Xenopus oocytes,we confirmed that nitrate transporter NRT1.5 can also act as an H+/K+ antiporter and directly mediates K+ release out of cells.In this study,our results demonstrate that NRT1.5 functions as a dual-role transporter for K+ and NO3-loading from root parenchyma cells into the xylem in Arabidopsis root,as well as serving as a key coordinator for K+/NO3-distribution in plants.