Integrated transcriptomic and targeted triterpenoid profiling reveals key enzymes in triterpenoid biosynthesis of Oplopanax elatus

Oplopanax elatus (O. elatus) is an endangered medicinal plant containing pharmacologically important triterpenoids; however, the biosynthetic mechanisms underlying their accumulation remain largely unknown. This study aimed to elucidate the metabolic and genetic basis for triterpenoid production by comparing root tissues at 0 weeks (0 W) and regenerated plantlets cultured for 8 weeks (8 W). Quantitative HPLC analysis revealed that the contents of lupeol, oleanolic acid, and betulin were markedly higher in 8 W regenerated tissues than in 0 W roots. To investigate the molecular basis of this increase, we performed comparative transcriptomic analysis and identified differentially expressed genes associated with triterpenoid biosynthesis. Among oxidosqualene cyclases (OSCs), beta-amyrin synthase (Gene_22342T) and lupeol synthase (Gene_05624T) showed threefold and 30-fold higher expression at 8 W, respectively, which was further validated by qRT-PCR. Phylogenetic analysis, conserved motif characterization, and protein–ligand docking confirmed that these genes function as key enzymes in triterpenoid skeleton formation. Our findings provide the first integrated biochemical and transcriptomic evidence explaining triterpenoid accumulation in regenerated O. elatus tissues and offer foundational insights for metabolic engineering and conservation-based utilization of this endangered plant.