Allopolyploid Brassica juncea is particularly enriched in sinigrin, a kind of 3C aliphatic glucosinolates (GSLs), giving rise to characteristic taste after picking. However, the molecular mechanism underlying 3C 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 MAM1s 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 3C and 4C 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 3C aliphatic GSLs biosynthesis. Our study provides insights into the molecular mechanism underlying the accumulation of 3C aliphatic GSLs, thereby facilitating the manipulation of aliphatic GSLs content in B. juncea.

多倍体芥菜型油菜特别富含芥子苷，一种3C脂肪族芥子油苷（GSL），在采摘后会产生独特的味道。但是，该物种中3C脂肪族GSL生物合成的分子机制仍然未知。在这项研究中，我们在全基因组范围内鉴定了GSLs代谢基因，这表明芥菜型假单胞菌亚基因组之间GSLs代谢基因的进化速率不同。从芥菜芽胞杆菌中鉴定到8个甲基硫代烷基苹果酸合酶（MAMs）同源物，其中6个MAM1位于叶绿体中，另外2个未检测到任何表达。此外，BjMAM1-4，BjMAM1-5和BjMAM1-6在叶片中的表达水平高于其他组织。沉默表达分析表明BjMAM1-4和BjMAM1-6在3C和4C脂肪族GSL积累中起作用。第二轮反应的底物选择特异性远低于第一轮反应的特异性，表明这些基因可能优先催化3C脂肪族GSL的生物合成。我们的研究提供了对3C脂肪族GSL积累的分子机制的见解，从而促进了芥菜中脂肪族GSLs含量的操纵。