Transcriptome analysis reveals the differential regulatory effects of red and blue light on nitrate metabolism in pakchoi (Brassica campestris L.)

Pakchoi (Brassica campestris L. ssp. chinensis) is an important leafy vegetable. Various light spectra, especially red and blue light, play vital roles in the regulation of nitrate metabolism. Information on the effects of red and blue light on nitrate metabolism at the transcriptome level in pakchoi is still limited, so this study used RNA sequencing technology to explore this molecular mechanism. Through pairwise comparisons with white LED light, 3 939 and 5 534 differentially expressed genes (DEGs) were identified under red and blue light, respectively. By Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, these unigenes were found to be involved in nitrate assimilation, plant-pathogen interaction, biosynthesis of secondary metabolites, and phenylpropanoid biosynthesis. The differential effects of light spectra on the nitrate concentration and metabolism-related enzyme activities were also confirmed at the physiological level. Several signal transduction modules, including Crys/Phys-COP1-HY5/HY5-like, were found to be involved in red and blue light-induced nitrate metabolism, and the transcript levels for this complex were consistent with the observed degree of nitrate assimilation. The expression patterns of 15 randomly selected DEGs were further validated using qPCR. Taken together, the results of this study could help improve our understanding of light spectrum-regulated nitrate metabolism in pakchoi at the transcriptome level.