Involved in the biosynthesis of macrocyclic lathyrane type diterpenoids (also called Euphorbia factors) natural products, including the cyclization route from casbene to jolkinol C, a precursor for ingenol mebutate that is used to treat actinic keratosis, a precancerous skin condition (PubMed:27506796). Catalyzes the conversion of 4,5,8-trihydroxycasbene into jolkinol C in presence of NAD (PubMed:27506796). Mediates also the formation of casbene dione derivative and 4-ketocasbene from 4-hydroxy-8-ketocasbene and 4-hydroxycasbene, respectively (PubMed:27506796). Together with CYP71D445, triggers the biosynthesis of 8-ketocasbene from 8-hydroxycasbene (PubMed:27506796). 4,5,8-trihydroxycasbene + 2 NAD(+) = 2 H(+) + jolkinol C + 2 NADH a secondary alcohol + NAD(+) = a ketone + H(+) + NADH a primary alcohol + NAD(+) = an aldehyde + H(+) + NADH Secondary metabolite biosynthesis; terpenoid biosynthesis. Homodimer. Expressed in mature seeds. Belongs to the short-chain dehydrogenases/reductases (SDR) family.