Required to form the C-22 double bond in the sterol side chain. Possesses in vitro C-22 desaturase activity toward 24-epi-campesterol and beta-sitosterol and produces brassicasterol and stigmasterol, respectively. No activity with campesterol. 5-dehydroepisterol + H(+) + NADPH + O2 = ergosta-5,7,22,24(28)-tetraen-3beta-ol + 2 H2O + NADP(+) Steroid biosynthesis; sterol biosynthesis. Expressed in the vascular tissues of roots, shoots, stems and leaves. Expressed in root tips, carpes, siliques and seeds. Not induced by pathogen infection. No visible phenotype under normal growth conditions, but production of brassicasterol is abolished. Plants overexpressing CYP710A2 show higher levels of brassicasterol/crinosterol and stigmasterol, and lower levels of 24-epi-campesterol/campesterol and beta-sitosterol than the wild-type. Belongs to the cytochrome P450 family.