Geranylgeranyl pyrophosphate synthase; part of the gene cluster that mediates the biosynthesis of the diterpenoid pyrones subglutinols A and B (PubMed:32286350). The first step of the pathway is the synthesis of the alpha-pyrone moiety by the polyketide synthase dpmaA via condensation of one acetyl-CoA starter unit with 3 malonyl-CoA units and 2 methylations (Probable). The alpha-pyrone is then combined with geranylgeranyl pyrophosphate (GGPP) formed by the GGPP synthase dpmaD through the action of the prenyltransferase dpmaC to yield a linear alpha-pyrone diterpenoid (Probable). Subsequent steps in the diterpenoid pyrone biosynthetic pathway involve the decalin core formation, which is initiated by the epoxidation of the C10-C11 olefin by the FAD-dependent oxidoreductase dpmaE, and is followed by a cyclization cascade catalyzed by the terpene cyclase dpmaB (Probable). The dehydrogenase dpmaF is then involved in tetrahydrofuran (THF) ring formation at the C5 unit to complete the formation of subglutinols A and B (PubMed:32286350). dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate (2E)-geranyl diphosphate + isopentenyl diphosphate = (2E,6E)-farnesyl diphosphate + diphosphate (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Diterpenoid pyrones display various biological activities and subglutinol A shows insecticidal and anti-HIV activities. Belongs to the FPP/GGPP synthase family.