Catalyzes the two steps reaction converting geranylgeranyl diphosphate to phytoene via prephytoene diphosphate. 2 (2E,6E,10E)-geranylgeranyl diphosphate = 15-cis-phytoene + 2 diphosphate Inhibited by inorganic pyrophosphate and hydroxyphenylglyoxal. Optimum pH is 7.6. Carotenoid biosynthesis; phytoene biosynthesis; all-trans-phytoene from geranylgeranyl diphosphate: step 1/1. Monomer. Expressed in fruits, at lower levels in leaves. Expressed during ripening. While the color of orange fruits is due either to the accumulation of beta-carotene, or due to only the accumulation of red and yellow carotenoids, all peppers studied have a wild type PSY1 enzyme. Belongs to the phytoene/squalene synthase family.