Dual O-methyltransferase/FAD-dependent monooxygenase; part of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:17074519, PubMed:15915645, PubMed:26938470). The perylenequinone chromophore of cercosporin absorbs light energy to attain an electronically-activated triplet state and produces active oxygen species such as the hydroxyl radical, superoxide, hydrogen peroxide or singlet oxygen upon reaction with oxygen molecules (PubMed:11701851). These reactive oxygen species cause damage to various cellular components including lipids, proteins and nucleic acids (PubMed:11701851). The first step of cercosporin biosynthesis is performed by the polyketide synthase CTB1 which catalyzes the formation of nor-toralactone (PubMed:23108075, PubMed:26938470). The starter unit acyltransferase (SAT) domain of CTB1 initiates polyketide extension by the selective utilization of acetyl-CoA, which is elongated to the heptaketide in the beta-ketoacyl synthase (KS) domain by successive condensations with six malonyl units introduced by the malonyl acyltransferase (MAT) domain. The product template (PT) domain catalyzes C4-C9 and C2-C11 aldol cyclizations and dehydrations to a trihydroxynaphthalene, which is thought to be delivered to the thioesterase (TE) domain for product release (PubMed:23108075). The bifunctional enzyme CTB3 then methylates nor-toralactone to toralactone before conducting an unusual oxidative aromatic ring opening (PubMed:17074519, PubMed:26938470). The O-methyltransferase CTB2 further methylates the nascent OH-6 of the CBT3 product, blocking further oxidation at this site before the reductase CTB6 reduces the 2-oxopropyl ketone at position C7, giving naphthalene (PubMed:17660442, PubMed:26938470). The FAD-dependent monooxygenase CTB5 in concert with the multicopper oxidase CTB12 are responsible for homodimerization of naphthalene with CTB7 installing the dioxepine moiety, finally producing cercosporin (PubMed:17660442, PubMed:30809363, PubMed:26938470). The fasciclin domain-containing protein CTB11 might act with CTB5 and CTB12 whereas the roles of CTB9 and CTB10 have still to be elucidated (By similarity). nor-toralactone + S-adenosyl-L-methionine = H(+) + S-adenosyl-L-homocysteine + toralactone H(+) + NADH + O2 + toralactone = 1-(3,4,5-trihydroxy-7-methoxynaphthalen-2-yl)propan-2-one + CO2 + NAD(+) Mycotoxin biosynthesis. Expression is positively regulated by the cercosporin cluster-specific transcription factor CTB8 (PubMed:17462021). Expression is also affected by nitrogen and carbon sources and pH, and is also controlled by another transcription activator, CRG1, previously shown to regulate cercosporin production and resistance (PubMed:17462021). Abolishes the production of cercosporin but accumulates the naphthopyrones nor-toralactone and toralactone, as well as the oxidation product of nor-toralactone, naphthoquinone (PubMed:17074519, PubMed:26938470). Adopts a dark yellow-brown coloration, with slight export of pigmented metabolites into the agar (PubMed:26938470). In the C-terminal section; belongs to the paxM FAD-dependent monooxygenase family. In the N-terminal section; belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.