A novel type III polyketide synthase encoded by a three-intron gene from Polygonum cuspidatum

Abstract

A type III polyketide synthase cDNA and the corresponding gene (PcPKS2) were cloned from Polygonum cuspidatum Sieb. et Zucc. Sequencing results showed that the ORF of PcPKS2 was interrupted by three introns, which was an unexpected finding because all type III PKS genes studied so far contained only one intron at a conserved site in flowering plants, except for an Antirrhinum majus chalcone synthase gene. Besides the unusual gene structure, PcPKS2 showed some interesting characteristics: (1) the CHS "gatekeepers" Phe215 and Phe265 are uniquely replaced by Leu and Cys, respectively; (2) recombinant PcPKS2 overexpressed in Escherichia coli efficiently afforded 4-coumaroyltriacetic acid lactone (CTAL) as a major product along with bis-noryangonin (BNY) and p-hydroxybenzalacetone at low pH; however, it effectively yielded p-hydroxybenzalacetone as a dominant product along with CTAL and BNY at high pH. Beside p-hydroxybenzalacetone, CTAL and BNY, a trace amount of naringenin chalcone could be detected in assays at different pH. Furthermore, 4-coumaroyl-CoA and feruloyl-CoA were the only cinnamoyl-CoA derivatives accepted as starter substrates. PcPKS2 did not accept isobutyryl-CoA, isovaleryl-CoA or acetyl-CoA as substrate. DNA gel blot analysis indicated that there are two to four PcPKS2 copies in the P. cuspidatum genome. RNA gel blot analysis revealed that PcPKS2 is highly expressed in the rhizomes and in young leaves, but not in the roots of the plant. PcPKS2 transcripts in leaves were induced by pathogen infection, but not by wounding.

Molecular analysis of a type III polyketide synthase gene in Fallopia multiflora

“…Nearly all the genes studied so far have a single intron between the first and second nucleotides of the Cys60 triplet (M. sativa CHS2 numbering); only a few exceptions have been reported. PcPKS2 from P. cuspidatum is encoded by a three-intron gene (Ma et al 2009). The genes coding for Antirrhinum majus CHS (AmCHS; Sommer & Saedler 1986) as well as Arabidopsis ASCL (AthASCL2) contain two introns each.…”

“…The clinically demonstrated major bioactive compounds of F. multiflora are various aromatic polyketides including stilbenes and anthraquinones (Lin et al 2003;Yao et al 2006); more precisely, 2,3,5,4'-tetra-hydroxy-stilbene-2-O-β-D-glucoside (TSG), emodin, rhein, physcion and chrysophanol. It is presumed that these aromatic com-pounds are biosynthesized via a polyketide pathway by PKSs (Samappito et al 2003;Ma et al 2009), but genes coding for PKSs responsible for their biosynthesis have not been isolated.…”

Type III polyketide synthases in natural product biosynthesis

“…This is followed by a cyclization reaction, leading to the formation of an aromatic tetraketide, naringenin chalcone ( Fig. 1E) (9). CHS is one of several type III PKSs that use 4-coumaroyl-CoA as the starter unit, which is synthesized by the upstream general phenylpropanoid pathway from L-Phe.…”

In vitro regeneration, Agrobacterium-mediated transformation, and genetic assay of chalcone synthase in the medicinal plant Echinacea pallida

“…S4). These conservative changes may change the structure and chemical properties of the protein, and differentially regulate anthocyanin and flavone synthesis (Wang et al 2007;Ma et al 2009;Ohno et al 2011). The different expression patterns of two homologous EpaCHSBs in tissues of E. pallida imply these two chalcone synthase paralogs possibly play distinct roles in different tissues.…”