Transcriptomic and metabolomic analysis reveals the mechanism underlying ABA-induced biosynthesis of glucosinolates and flavonoids in rapeseed under Cd stress

Cadmium (Cd) contamination represents a major challenge to agricultural output and food security. A combined analysis of transcriptome and metabolome was conducted on rapeseed seedlings exposed to Cd stress $50\mu \text{mol}/L$ with or without exogenous Abscisic acid (ABA) $5\mu \text{mol}/L$ supplementation. The results indicated that the biosynthesis pathways of glucosinolates and flavonoids were prominently enriched in the dataset of differentially expressed genes and metabolites. Notably, ABA treatment effectively up-regulated the expression of critical genes involved in glucosinolate (GGP1, CYP83B1, IMGT5, etc.) and flavonoid biosynthesis (4CL4, TT5, TT6, etc.), which had been repressed by Cd exposure, thereby restoring their metabolic levels. Additionally, exogenous ABA was found to restore the amounts of seven glucosinolates and ten flavonoids to normal ranges, as their production had been hindered by Cd exposure. These results indicate that ABA exerts a vital impact on boosting Cd resistance in oilseed rape through the control of transcriptional processes involved in GSL and flavonoid metabolic pathways, thereby adjusting the buildup of these protective secondary metabolites.