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. Can rescue the phenotype in the Arabidopsis max3 mutant. 9-cis-beta-carotene + O2 = 9-cis-10'-apo-beta-carotenal + beta-ionone Binds 1 Fe(2+) ion per subunit. Expressed in vascular bundles of roots, leaves, stems and panicles. By auxin. Dwarf phenotype with increased branching and tiller number, and strong reduction of the root levels of strigolactones. The branching phenotypes of the ccd7/max3 and ccd8b/max4 mutants can be rescued by exogenous treatment with the synthetic strigolactone analogs GR24 and 4BD. Belongs to the carotenoid oxygenase family.