Converts phytoene into zeta-carotene via the intermediary of phytofluene by the symmetrical introduction of two double bonds at the C-11 and C-11' positions of phytoene with a concomitant isomerization of two neighboring double bonds at the C9 and C9' positions from trans to cis. 15-cis-phytoene + 2 a plastoquinone = 9,9',15-tri-cis-zeta-carotene + 2 a plastoquinol Carotenoid biosynthesis; lycopene biosynthesis. Homotetramer. Expressed in flower buds and lips. Lower expression in leaves and roots. Expressed during floral development. Belongs to the carotenoid/retinoid oxidoreductase family.