Phytoene desaturase (zeta-carotene-forming) (, CrtIa, 2-step phytoene desaturase (ambiguous), two-step phytoene desaturase (ambiguous)) is an enzyme with systematic name 15-cis-phytoene:acceptor oxidoreductase (zeta-carotene-forming). This enzyme catalyses the following chemical reaction
The enzyme is involved in carotenoid biosynthesis.