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 spectrumregulated nitrate metabolism in pakchoi at the transcriptome level.

CPSF30-L-mediated recognition of mRNA m^(6)A modification controls alternative polyadenylation of nitrate signaling-related gene transcripts in Arabidopsis

N6-methyladenosine(m^(6)A),a ubiquitous internal modification of eukaryotic mRNAs,plays a vital role in almost every aspect of mRNA metabolism.However,there is little evidence documenting the role of m^(6)A in regulating alternative polyadenylation(APA)in plants.APA is controlled by a large protein-RNA complex with many components,including CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30(CPSF30).In Arabidopsis,CPSF30 has two isoforms and the longer isoform(CPSF30-L)contains a YT512-B Homology(YTH)domain,which is unique to plants.In this study,we showed that CPSF30-L YTH domain binds to m^(6)A in v itro.In the cpsf30-2 mutant,the transcripts of many genes including several important nitrate signaling-related genes had shifts in polyadenylation sites that were correlated with m^(6)A peaks,indicating that these gene transcripts carrying m^(6)A tend to be regulated by APA.Wild-type CPSF30-L could rescue the defects in APA and nitrate metabolism in cpsf30-2,but m^(6)A-binding-defective mutants of CPSF30-L could not.Taken together,our results demonstrated that m^(6)A modification regulates APA in Arabidops is and revealed that the m^(6)A reader CPSF30-L affects nitrate signaling by controlling APA,shedding new light on the roles of the m^(6)A modification during RNA 3-end processing in nitrate metabolism.