Transcriptome Profiling Reveals Candidate Key Genes Involved in Sinigrin Biosynthesis in Brassica nigra

Glucosinolates (GSLs) are important secondary metabolites in Brassicales related to insect and disease resistance, flavor formation, and human health. Here, we determined the GSL profile with sinigrin as the predominant GSL in Brassica nigra. A total of 184 GSL biosynthetic genes (BniGSLs) were identified in B. nigra by a genome-wide search for orthologs of 82 of the 95 known GSL genes in Arabidopsis thaliana. Transcriptome data demonstrated that at least one BniGSL was highly expressed in stems and leaves at each step of the sinigrin synthesis pathway, which ensured the synthesis of a large amount of sinigrin in B. nigra. Among these key candidates of BniGSLs, the high expression of BniMAM1-2, BniCYP79F1, and BniAOP2-1/2, and the absence of MAM3 and AOP3, may contribute remarkably to the synthesis and accumulation of sinigrin. In addition, the low expression of some key BniGSLs partially explains the low content of indolic and aromatic GSLs in B. nigra. This study provided a genetic explanation for the formation of the unique GSL profile with sinigrin as the main GSL in B. nigra. The results of this study will be valuable for further functional analysis of BniGSLs and genetic improvement of GSLs in B. nigra and other Brassica species.