NLP6/7-mediated nitrate signaling facilitates high-affinity potassium uptake and enhances tolerance to low potassium environments in Arabidopsis.

Abstract

Balancing the acquisition of the macronutrients nitrogen (N) and potassium (K) is critical for plant growth, yet the mechanisms that balance N and K acquisition remain poorly understood. Here, we show that the NIN-LIKE PROTEIN7 (NLP7) transcription factor, which mediates nitrate signaling, plays a crucial role in promoting K acquisition in Arabidopsis. K⁺ uptake activity was reduced in the nlp7 mutant and nlp6nlp7 double mutant but enhanced in the NLP7-overexpressing line. Consistently, these mutants were hypersensitive to K deficiency, whereas the NLP7-overexpressing line displayed increased tolerance. Transcriptome analysis of the nlp6nlp7 mutant suggested that NLP7 activates several critical K-related genes, including HAK5, a transporter gene essential for K⁺ uptake from soil, and SKOR, a channel gene critical for root-to-shoot transport of K⁺. Using co-transfection assays, gel electrophoresis mobility shift assays, and chromatin immunoprecipitation assays, we demonstrate that NLP7 directly interacts with and activates the promoters of these two genes. Furthermore, the enhanced K⁺ uptake and improved K deficiency responses driven by NLP7 overexpression were mitigated in the hak5 and skor mutants, demonstrating the significant physiological role of NLP7-induced activation of these genes. Although HAK5 and SKOR responded differently to K deficiency, both genes were activated similarly by NLP7 under K-sufficient and K-deficient conditions. Together, these findings suggest that K deficiency-induced regulation and nitrate-responsive regulation operate through independent transcriptional mechanisms but collaborate to ensure appropriate K acquisition under diverse N and K conditions, especially when K availability is limiting.