Two type III polyketide synthases from Polygonum cuspidatum: gene structure, evolutionary route and metabolites

In our recent work (Ma et al., in Planta 229(3):457–469, 2009a and 229(4):1077–1086, 2009b), two three-intron type III PKS genes, PcPKS1 and PcPKS2, were isolated from Polygonum cuspidatum Sieb. et Zucc. Phylogenetic and functional analyses revealed PcPKS1 is a three-intron chalcone synthase (CHS) gene, and PcPKS2 is found to be a three-intron benzalacetone synthase (BAS) gene. The regular CHS encoded by a single intron gene have not been isolated and characterized from P. cuspidatum. In this work a further CHS with one intron (PcPKS3) and a stilbene synthase (STS) gene with three-intron (PcPKS5) were isolated and characterized by functional and phylogenetic analyses. In comparison with PcPKS1, a bifunctional enzyme with both CHS and BAS activity, the enzymatic product of recombinant PcPKS3 was naringenin, bis-noryangonin (BNY) and 4-coumaroyltriacetic acid lactone (CTAL) occurred as side products. The PcPKS5 synthesized resveratrol and a trace amount of naringenin from p-coumaroyl-CoA. To our knowledge, PcPKS5 is the first reported three-intron STS gene in flowering plants. In this work, we speculated that this involved a possible evolutionary route of plant-specific type III PKS superfamily in P. cuspidatum.