Integrative Analyses of Metabolites and Transcriptome Reveal the Metabolic Pattern of Glucosinolates in Potherb Mustard (Brassica juncea var. multiceps)

Potherb mustard (Brassica juncea var. multiceps) is one of the most commonly consumed leafy vegetable mustards, either fresh or in pickled form. It is rich in glucosinolates, whose hydrolyzed products confer potherb mustard's distinctive flavor and chemopreventive properties. In this study, the composition and content of glucosinolates, as well as the hydrolysis pattern of sinigrin were investigated in potherb mustard leaves of different varieties. Variations in the glucosinolate profile and accumulation were observed among the potherb mustard varieties studied, with sinigrin being the predominant one in all varieties, accounting for 81.55% to 97.27%. Sinigrin tended to be hydrolyzed to isothiocyanate (ITC) rather than epithionitrile (EPN) in potherb mustard, while 3-butenyl nitrile (SIN-NIT) could be hardly detected. Transcriptome analysis revealed a higher expression level of numerous genes involved in aliphatic glucosinolate biosynthesis in X11 compared to X57, corresponding to the higher aliphatic glucosinolate accumulation in X11 (91.07 mu mol/g) and lower level in X57 (25.38 mu mol/g). ESM1 is known to repress nitrile formation and favor isothiocyanate production during glucosinolate hydrolysis. In this study, all four ESM1s showed a higher expression level in X11 compared to X57, which may determine the hydrolysis pattern of sinigrin in potherb mustard. Altogether, our findings shed light on the glucosinolate metabolic pattern in potherb mustard, which will also facilitate the engineering of metabolic pathways at key checkpoints to enhance bioactive compounds for tailored flavor or pharmaceutical needs.