Non-reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of orcinol depsidone grayanic acid (GRA), the only major secondary metabolite known in C.grayi (PubMed:21289108). The first step consists in the ring and depside synthesis by PKS16 leading to 4-O-demethylsphaerophorin, involving different orcinol-like rings, one with acetyl CoA and the other with octanoyl CoA as the starter (Probable). Further depsidone formation by the GRA cluster-specific cytochrome P450 leads to 4-O-demethylgrayanic acid (Probable). Finally, the cluster specific O-methyltransferase probably converts the 4-O-demethylgrayanic acid into grayanic acid (Probable). Secondary metabolite biosynthesis. Belongs to the cytochrome P450 family.