Oleanane-type triterpenoid saponins are the primary medicinal components of . During saponin biosynthesis in , various members of the 2,3-oxidosqualene cyclase (OSC) gene family can direct 2,3-oxidosqualene into triterpene saponin and sterol synthesis pathways. However, the precise molecular mechanism underlying this phenomenon remains unclear. We initially screened for β-amyrin synthase 1 (bAS1) and cycloartenol synthase 1 (CAS1) among 10 genes using genome-wide identification and correlation analysis. Subcellular localization, catalytic experiments, and transient overexpression demonstrated that bAS1 and CAS1 catalyze the formation of the triterpene skeleton β-amyrin and sterol precursor cycloartenol exclusively in the cytoplasm, enhancing and inhibiting the biosynthesis of oleanane-type saponins, respectively. Results from site-directed mutagenesis and molecular docking indicated that W-WY and Y-WH triplets characterized the active sites of , respectively. GUS (β-glucuronidase) staining and electrophoretic mobility shift assay (EMSA) experiments on the promoter region revealed that various colored light quality, DNA methylation, and five transcription factors (NAC047, NAC098, WRKY40, MYB4, and ERF66) regulated the expression of and . This study provides preliminary insights into the molecular mechanisms by which and regulate saponin synthesis in .