Polyketide synthase, which uses acetyl-CoA and two condensation reactions with malonyl-CoA to form triacetic acid lactone (also called methylpyrone), a precursor of phytoalexin. May participate in insect and pathogen resistance. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family. Ref.3 has shown that this is not a chalcone synthase, but a pyrone synthase.