Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of various drimane-type sesquiterpene esters, compounds that exhibit diverse biological activities and are widely present in eukaryotes (PubMed:34468074). The pathway begins with the synthesis of the backbone drimenol by the terpene cyclase drtB using farnesyl pyrophosphate (FPP) as substrate (PubMed:34468074). The cytochrome P450 monooxygenase drtD is then responsible for the hydroxylations at C-6, C-9 and C-12, as well as the oxidation of hydroxyl groups at C-6 and C-11 to a ketone and an aldehyde, respectively (PubMed:34468074). Then, the biosynthesis can go in two directions, either the hydroxylated drimenol is further hydroxylated at C-2 and C-3 by an enzyme(s) not associated with the drt cluster, or the FAD-binding oxidoreductase drtC further oxidizes C-11 or C-12 to form the butyrolactone ring (PubMed:34468074). DrtB, drtD and drtC are solely responsible for the formation of the different drimane structures observed during drimane sesquiterpenes biosynthesis (PubMed:34468074). The polyketide synthase drtA synthesizes different lengths (C6 and C8) of PKS chains, which are then oxidized to varying degrees by the short-chain dehydrogenase drtF (PubMed:34468074). Finally, these PKS chains are transferred onto drimane sesquiterpenes by the acyltransferase drtE, forming the sesquiterpene esters (PubMed:34468074). In addition to the different fatty acyl-CoA chains produced by drtA, drtE is also able to use cinnamoyl-CoA as a substrate (PubMed:34468074). Secondary metabolite biosynthesis; terpenoid biosynthesis. Abolishes the production of all the drimane sesquiterpene. The various drimane-type sesquiterpene esters produced by the A.calidoustus drt cluster include asperiene C, asperiene A, (6-Strobilactone-B) ester of (E,E)-6-carbonyl-7-hydroxy-2,4-octadienoic acid, ustusolate A, ustusolate C, ustusolide E, ustusoic acid A, (2'E,4'E)-6-(1'-carboxyhexa-2',4',-diene)-9-hydroxy-drim-7-ene-11,12-olide, RES-1149-2, as well as the 3 newly identified compounds calidoustene A, calidoustene B and calidoustene C. Belongs to the cytochrome P450 family.