Component of the triterpene saponins (e.g. ginsenosides or panaxosides) and phytosterols biosynthetic pathways (PubMed:15356323, PubMed:27746309, PubMed:29378087). Catalyzes the biosynthesis of squalene (PubMed:15356323). 2 (2E,6E)-farnesyl diphosphate + H(+) + NADH = 2 diphosphate + NAD(+) + squalene 2 (2E,6E)-farnesyl diphosphate + H(+) + NADPH = 2 diphosphate + NADP(+) + squalene Terpene metabolism; lanosterol biosynthesis; lanosterol from farnesyl diphosphate: step 1/3. Mostly expressed in the shoot apex (buds) and roots, and, to a lower extent, in stems, leaves, flowers and seeds. Rapid decrease in 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:25642758, Ref.6, PubMed:15538577, Ref.10). 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.6). 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.12). Stimulated by the plant cell wall-derived elicitor oligogalacturonic acid (Ref.6). Influenced in roots by photosynthetically active radiation (PAR), and in leaves by relative humidity (PubMed:30577538). Belongs to the phytoene/squalene synthase family.