Plant type III polyketide synthases (PKSs) that catalyzes the condensation of malonyl-CoA units with various CoA ester starter molecules to generate a diverse array of natural products including long-chain alkyl alpha-pyrones. Accepts up to C(20) chain-length fatty acyl CoAs as starter substrates, and carries out sequential condensations with malonyl-CoA to produce triketide and tetraketide alpha-pyrones, potential sporopollenin precursors (PubMed:19043200, PubMed:21193570). Favorite substrates for are midchain- and v-hydroxylated fatty acyl-CoAs (e.g. 12-hydroxyoctadecanoyl-CoA and 16-hydroxyhexadecanoyl-CoA). Required for pollen development and sporopollenin biosynthesis, the major constituent of exine in the outer pollen wall (PubMed:21193570, PubMed:20442277). In vitro, can use 4-coumaroyl-coenzyme A as substrate to produce bis-noryangonin and fatty acyl-coenzyme A as substrate to produce medium-chain alkyl pyrones. May play a role in both the synthesis of pollen fatty acids and phenolics found in exine (PubMed:20442277). kcat is 0.11 min(-1) with n-dodecanoyl-CoA as substrate for the production of the triketide alpha-pyrone (at pH 7 and 30 degrees Celsius)(PubMed:19043200). kcat is 2.8 msec(-1) with 16-OH-C16-CoA as substrate, 5 msec(-1) with 12-OH-C18-CoA as substrate and 0.13 msec(-1) with C16-CoA as substrate (PubMed:21193570). Optimum pH is 7 (at 30 degrees Celsius). Secondary metabolite biosynthesis; flavonoid biosynthesis. Homodimer (By similarity). Interacts with 4CLL1/ACOS5 and TKPR1 (PubMed:23632852). Expressed in flowers and flower buds (at protein level), and, at very low levels, in roots, seedlings, leaves and stems (PubMed:21193570, PubMed:20442277). Mostly confined to anther tapetal cells (PubMed:23632852). Most abundant in the youngest flower buds, but levels decline as flowers mature. Specifically and transiently expressed in tapetal cells during microspore development in anthers (at protein level). Pollen exine layer defects. Reduced accumulation of flavonoid precursors and flavonoids in developing anthers. Plants lacking both PKS-A and PKS-B are completely male sterile, with no apparent exine, thus leading to pollen grain collapse under vacuum. Altered pollen-stigma adhesion. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.