Involved in the biosynthesis of isorenieratene, a carotenoid with aromatic end groups (PubMed:10395965). Catalyzes the introduction of two additional double bonds into each ionone ring of beta-carotene to produce isorenieratene. The reaction includes an intramolecular methyl transfer from position C1 to position C2 of the ring (PubMed:10395965). 2 A + a carotenoid beta-end derivative = a carotenoid phi-end derivative + 2 AH2 Carotenoid biosynthesis. Deletion of the gene leads to accumulation of beta-carotene. Belongs to the carotenoid/retinoid oxidoreductase family.