Comparative Transcriptomics Reveal the Mechanisms Underlying the Glucosinolate Metabolic Response in Leaf Brassica juncea L. under Cold Stress

Glucosinolates (GSLs) are not only a unique flavor substance from leaf B. juncea but also a major secondary metabolite produced in response to abiotic stresses. Cold stress is one of the most common abiotic stresses in leaf B. juncea; however, the metabolic response pattern of GSLs in leaf B. juncea under cold stress has not yet been reported. In the present study, we analyzed the GSLs content of leaf B. juncea under cold stress and found that it increased and subsequently decreased. According to RNA-seq data, genes related to the synthesis of aliphatic GSLs were significantly upregulated following 24 h of cold stress; genes related to the synthesis of indole GSLs were significantly upregulated following 48 h of cold stress; and BjBGLU25 and BjBGLU27 were significantly upregulated. Further analysis of the correlation between transcription factors and GSLs content revealed that MYB, ERF, IQD, and bHLH may be involved in regulating the GSLs response pattern in leaf B. juncea under cold stress. In particular, an unreported transcription factor, BjMYBS3 (BjuVA05G33250), was found to play a possible role in the synthesis of aliphatic GSLs. And the external application of GSLs increased the ability of leaf B. juncea to cope with cold stress.