Transcriptomic data of developing siliques of three Brassica juncea (L.) with contrasting seed glucosinolate abundance and composition

Though glucosinolate (GSL) accumulation is a key determinant of the economic value of Brassica juncea, the underlying mechanisms remain poorly understood, limiting the ability to realize the full potential of this versatile crop. Low GSL levels in seeds are a key breeding target to develop B. juncea into an oil crop, while high levels of beneficial GSL (i.e. sinigrin) are desirable in cultivars for condiment industries. Comparative transcriptomics of two high GSL lines with different predominant aliphatic GSLs (i.e. sinigrin and gluconapin) against a low GSL line was used to identify key drivers of GSL accumulation in B. juncea seeds. RNA sequencing data from developing siliques at seed filling stage revealed an overall higher GSL metabolic activity in the low GSL line. Though known key genes of GSL biosynthesis and transport, including a copy of MAM1 and GTR2 were expressed stronger in the high GSL backgrounds, many candidates of GSL biosynthesis, regulation and degradation were found to be expressed at higher rates in the low GSL line. Collectively, differential activity of GSL catabolism, rather than anabolism was found the main driver behind the observed seed GSL phenotypes. Finally, a copy of CYP79F1 was identified as a strong candidate for preferential accumulation of sinigrin.

尽管硫代葡萄糖苷（glucosinolate, GSL）的积累是芥菜型油菜（Brassica juncea）经济价值的核心决定因素，但其潜在调控机制仍不甚明晰，极大限制了这一多功能作物的开发潜力。将芥菜型油菜培育为油料作物时，种子低GSL含量是关键育种目标；而调味品工业所需的品种则需积累高含量的有益GSL，即黑芥子苷（sinigrin）。本研究以低GSL品系为对照，对两个优势脂肪族GSL组分不同的高GSL品系（分别积累黑芥子苷（sinigrin）与葡糖芸苔苷（gluconapin））开展比较转录组分析，以鉴定芥菜型油菜种子中GSL积累的关键调控因子。对籽粒灌浆期发育角果的RNA测序（RNA sequencing）数据进行分析后发现，低GSL品系的GSL整体代谢活性更高。尽管已知的GSL生物合成与转运关键基因（包括MAM1和GTR2的一个拷贝）在高GSL遗传背景中表达量更高，但大量参与GSL生物合成、调控及降解的候选基因在低GSL品系中表达水平显著上调。综合分析表明，GSL分解代谢而非合成代谢的差异活性，是导致观测到的种子GSL表型差异的主要驱动因素。最后，本研究鉴定到CYP79F1的一个拷贝可作为黑芥子苷偏好积累的强候选调控基因。