Involved in strigolactones biosynthesis by cleaving asymmetrically a variety of linear and cyclic carotenoids at the 9-10 double bond. Produces one C(13) beta-ionone and the C(27) 10'-apo-beta-carotenal. Strigolactones are hormones that inhibit tillering and shoot branching through the MAX-dependent pathway, contribute to the regulation of shoot architectural response to phosphate-limiting conditions and function as rhizosphere signal that stimulates hyphal branching of arbuscular mycorrhizal fungi and trigger seed germination of root parasitic weeds. No activity on lycopene, lutein, zeaxanthin, violaxanthin or neoxanthin. Probably not involved in abscisic acid biosynthesis. 9-cis-beta-carotene + O2 = 9-cis-10'-apo-beta-carotenal + beta-ionone Binds 1 Fe(2+) ion per subunit. addition of methanol to in vitro assays has a strong stimulatory effect. Expressed in flowers, siliques, inflorescence stems, petiole, leaves and roots. Increased shoot branching. The branching phenotypes of the max1, ccd7/max3 and ccd8/max4 mutants can be rescued by exogenous treatment with the synthetic strigolactone analogs GR24 and 4BD. Belongs to the carotenoid oxygenase family. Introns retention.