Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of abscisic acid (ABA), a phytohormone that acts antagonistically toward salicylic acid (SA), jasmonic acid (JA) and ethylene (ETH) signaling, to impede plant defense responses. The first step of the pathway catalyzes the reaction from farnesyl diphosphate to alpha-ionylideneethane performed by the alpha-ionylideneethane synthase abl3 via a three-step reaction mechanism involving 2 neutral intermediates, beta-farnesene and allofarnesene. The cytochrome P450 monooxygenase abl1 might then be involved in the conversion of alpha-ionylideneethane to alpha-ionylideneacetic acid. Alpha-ionylideneacetic acid is further converted to abscisic acid in 2 steps involving the cytochrome P450 monooxygenase abl2 and the short-chain dehydrogenase/reductase abl4, via the intermediates 1'-deoxy-ABA or 1',4'-trans-diol-ABA, depending on the order of action of these 2 enzymes. Abl2 is responsible for the hydroxylation of carbon atom C-1' and abl4 might be involved in the oxidation of the C-4' carbon atom. The cytochrome monooxygenase abl5 seems not essential for the biosynthesis of ABA and its function remains to be identified