Plant-specific type III polyketide synthase (PKS) that catalyzes the one-pot formation of the C6-C7-C6 diarylheptanoid scaffold of bisdemethoxycurcumin by the condensation of two molecules of 4-coumaroyl-CoA and one molecule of malonyl-CoA. 2 4-coumaroyl-CoA + H(+) + H2O + malonyl-CoA = bisdemethoxycurcumin + 2 CO2 + 3 CoA Secondary metabolite biosynthesis; flavonoid biosynthesis. Homodimer. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.