Ectopic expression of Brassica rapa BrNLP7.1 reveals its conserved role in nitrate assimilation and signaling

Nitrate stands as a primary nitrogen (N) source for plants across diverse natural habitats and agricultural systems. It serves as both a vital nutrient and a key signaling molecule crucial for plant growth and development. The NIN-like protein 7 (NLP7) functions as a central transcription factor and intracellular nitrate sensor in Arabidopsis thaliana (Arabidopsis), yet its orthologs remain uncharacterized in Chinese cabbage (Brassica rapa subsp. pekinensis), a globally important vegetable crop. In this study, the BrNLP7.1 gene was identified based on its homology with NLP7 in Arabidopsis, and its role in mediating nitrate assimilation and signal transduction was characterized. Ectopic overexpression of BrNLP7.1 in the Arabidopsis nlp7 mutant rescued the stunted growth phenotype, restored nitrate content and nitrate reductase activity, and recovered the expression of nitrate-responsive gene. Yeast one-hybrid assays and transient expression assays demonstrated that BrNLP7.1 directly binds to the nitrate-responsive cis-element in target gene promoters and activates transcription. Furthermore, microscale thermophoresis analysis revealed that the N-terminal region of BrNLP7.1 directly binds nitrate. Collectively, these findings establish BrNLP7.1 as a functional ortholog of NLP7 involved in nitrate-responsive signaling.