Component of the triterpene saponins (e.g. ginsenosides or panaxosides) and phytosterols biosynthetic pathways (PubMed:29378087). Catalyzes the biosynthesis of squalene (By similarity). 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. Induced methyl jasmonate (MeJA) in adventitious roots. Belongs to the phytoene/squalene synthase family.