A Candidate Gene Association Approach Combined with QTL Mapping Reveals the Genetic Architecture of Glucosinolate Content in Brassica rapa Leaves

Glucosinolates are sulfur-rich secondary metabolites mainly found in Brassicacea family. GSLs and their degradation products plays an important role in human health, pathogen and insect prevention, as well as in special flavors and tastes. We firstly performed a conventional QTL analysis using a B. rapa segregated population combined with candidate gene association approach by using natural population in order to identify the genomic region and genes regulating glucosinolates biosynthesis in B. rapa crops. Both QTL and association mapping result revealed that  paralogous of R2R3 MYB transcription factor, MAM gene family and BCAT-4 on A02, A03, A04, A07 syntenic region regulated the individual, three types and total aliphatic glucosinolate with gene redundancy function, guaranteeing the effective biosynthesis and metobolisam of glucosinolate. All of these associated genes had a high level of linkage disequilibrium in B. rapa genome. Moreover, two haplotypes forming by four SNPs in B. rapa MYB28b gene were significant related to glucosinolate content. Haplotype II with minor allele frequency in B. rapa could be used for selecting high gluconapin, aliphatic and total glucosinolate content.