Identification of MAM1s in Regulation of 3C Glucosinolates Accumulation in Allopolyploid Brassica juncea

Allopolyploid Brassica juncea is particularly enriched in sinigrin, a kind of 3 C aliphatic glucosinolates(GSLs), giving rise to characteristic taste after picking. However, the molecular mechanism underlying 3 C aliphatic GSLs biosynthesis in this species remains unknown. In this study,we genome-widely identified GSLs metabolic genes, indicating different evolutionary rate of GSLs metabolic genes between subgenomes of B.juncea. Eight methythioalkylmalate synthase(MAMs) homologs were identified from B. juncea, in which six MAM1 s were located in chloroplast and the other two were not detected with any expression. Furthermore, BjMAM1-4, BjMAM1-5, and BjMAM1-6 displayed higher expression levels in leaves than other tissues. Silenced expression analysis revealed that BjMAM1-4 and BjMAM1-6 function in 3 C and 4 C aliphatic GSLs accumulation. The specificity of the substrate selection for the second cycle reaction is much lower than that of the first cycle, suggesting these genes may preferentially catalyze 3 C aliphatic GSLs biosynthesis. Our study provides insights into the molecular mechanism underlying the accumulation of 3 C aliphatic GSLs, thereby facilitating the manipulation of aliphatic GSLs content in B. juncea.