Molecular Characterization and Expression Analysis of MYB Transcription Factors Involved in the Glucosinolate Pathway in Chinese Cabbage (Brassica rapa ssp. pekinensis)

Chinese cabbage (Brassica rapa) is a perennial crucifer vegetable that has long been used for forage. Crucifers are rich sources of glucosinolates (GSLs), which are anti-carcinogenic in humans and involved in plant defense responses. Myeloblastosis (MYB) proteins are a large family of transcription factors (TFs) in plants and play major regulatory roles in many biological processes. We identified 14 functional R2R3-MYB genes involved in glucosinolate biosynthesis in B. rapa ssp. pekinensis. Bioinformatic analysis of their phylogeny, protein motifs, gene interaction network, and molecular characteristics showed that Chinese cabbage MYB genes are comparable to those of Arabidopsis thaliana. The expression levels of the 14 BrMYB genes under fluorescent lamp, blue, and red light were quantitated using qRT-PCR analysis. Almost all of the R2R3-BrMYBs were upregulated and expressed more under red light than under fluorescent lamp or blue light, except BrMYB34s. We also calculated the total GSLs under each light condition. The total GSL content was higher under red light than under fluorescent lamp or blue light. Furthermore, the individual glucosinolates, comprised of four aliphatic GSLs (progoitrin, sinigrin, gluconapin, and glucobrassicanapin) and one indolic GSL (glucobrassicin), were higher under red light than the other light conditions. The relationships between light quality and glucosinolate biosynthesis require further investigation.