Involved in the biosynthesis of C30 carotenoids. Catalyzes four successive dehydrogenation reactions that lead to the introduction of four double bonds into 4,4'-diapophytoene (dehydrosqualene) to yield 4,4'-diapolycopene. 15-cis-4,4'-diapophytoene + 4 FAD + 4 H(+) = all-trans-4,4'-diapolycopene + 4 FADH2 Carotenoid biosynthesis. Cells lacking this gene accumulate the colorless C30 carotenoid precursor 4,4'-diapophytoene. Belongs to the carotenoid/retinoid oxidoreductase family.