Catalyzes the iterative condensations of 8 molecules of malonyl-CoA to produce aromatic octaketides, SEK4 and SEK4b, the products of the minimal polyketide synthase for the benzoisochromanequinone actinorhodin. May be involved in the biosynthesis of the octaketide barbaloin. kcat is 0.094 min(-1). Optimum pH is 7.5. Secondary metabolite biosynthesis; flavonoid biosynthesis. Homodimer. A.arborescens is a medicinal plant rich in aromatic polyketides, such as pharmaceutically important aloenin (hexaketide), aloesin (heptaketide) and barbaloin (octaketide). Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.