Expression profiles of BrMYB transcription factors related to glucosinolate biosynthesis and stress response in eight subspecies of Brassica rapa

Brassica rapa is a polyploid species with phenotypically diverse cultivated subspecies. Glucosinolates (GSLs) are secondary metabolites that contribute to anticarcinogenic activity and plant defense in Brassicaceae. Previously, complete coding sequences of 13 BrMYB transcription factors (TFs) related to GSL biosynthesis were identified in the B. rapa genome. In the present study, we investigated GSL content and expression levels of these BrMYB TFs in 38 accessions belonging to eight subspecies of B. rapa. Twelve identified GSLs were detected and were classified into three chemical groups based on patterns of GSL content and expression profiles of the BrMYB TFs. GSL content and BrMYB TF expression levels differed among genotypes, including B. rapa subspecies pekinensis, chinensis and rapa. BrMYB28.3, BrMYB51.1 and BrMYB122.2 positively regulated GSL content in 38 accessions. Furthermore, expression levels of BrMYB28s and BrMYB34.3 increased under most abiotic and biotic stress treatments. The three BrMYB51 paralogs also showed drastically increased expression levels after infection with Pectobacterium carotovorum. The results of the present study improve our understanding of the functional diversity of these 13 BrMYB TFs during the evolution of polyploid B. rapa.