Component of the triterpene saponins (e.g. ginsenosides or panaxosides) and phytosterols biosynthetic pathways (PubMed:19857882, PubMed:27746309, PubMed:29378087). Catalyzes the first oxygenation step in sterol biosynthesis and is suggested to be one of the rate-limiting enzymes in this pathway (By similarity). O2 + reduced [NADPH--hemoprotein reductase] + squalene = (S)-2,3-epoxysqualene + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Terpene metabolism; lanosterol biosynthesis; lanosterol from farnesyl diphosphate: step 2/3. Mostly expressed in flower buds and leaves, and, to a lower extent, at high levels thought, in roots and petioles (PubMed:19857882, PubMed:30577538). In petioles, preferentially observed in vascular bundle tissue (phloem cells and parenchymatous cells near xylem) and resin ducts (PubMed:19857882). Rapid decrease in roots and leaves from the leaf opened to the green fruit stage (PubMed:30577538). At the leaf opened stage, accumulates mostly in leaves (PubMed:30577538). Induced by jasmonic acid (JA) and methyl jasmonate (MeJA) in adventitious roots (PubMed:15356323, PubMed:15538577, PubMed:19857882, Ref.4). Induced by chitosan (CHN) (PubMed:15493471). Accumulates upon Cle-mediated signaling, an elicitor derived from fungal cell walls of C.lagenarium, thus inducing the accumulation of saponins (PubMed:15821288). Triggered by ethylene (ACC), rose bengal (RB), nitric oxide (NO) (PubMed:15821288). Accumulates in response to hydrogen peroxide (H(2)O(2)) (PubMed:15821288, Ref.4). Accumulates in the presence of squalene (PubMed:19857882). Induced by N,N'-dicyclohexylcarbodiimide (DCCD) in a nitric oxide (NO) dependent manner thus leading to increased ginsenosides accumulation (PubMed:23467002). Induced by A.niger mycelium-derived elicitor, thus improving ginsenosides production in adventitious roots culture (PubMed:27746309). Triggered by vanadate (Ref.13). Stimulated by the plant cell wall-derived elicitor oligogalacturonic acid (Ref.4). Accumulates under heavy metal stress in the presence of CdCl(2) (PubMed:23232757). Influenced in roots by temperature and photosynthetically active radiation (PAR), and in leaves by relative humidity and rain (PubMed:30577538). Reduced ginsenoside production. Strong up-regulation of squalene epoxidase 2 (SQE2) and cycloartenol synthase (OSCPNX1) expression resulting in an enhanced accumulation of phytosterol (campesterol, stigmasterol and sitosterol). Belongs to the squalene monooxygenase family.