Functional Analysis Of StPKS Gene Regulating Melanin Synthesis And Pathogenicity Of Setosphaeria Turcica

A polyketide synthase gene of Setosphaeria turcica was cloned in our laboratory at the earlier research. In order to confirm the function of StPKS gene in DHN melanin biosynthesis and pathogenicity, RNA interference and gene knock-out techniques were used to construct StPKS gene silent transformants and deleted mutants. The founction of the StPKS gene was identified by analyzing the mutant, the main results were as follows: The transformation vectors pSilent-1 and pBU, were used to construct StPKS RNAi and homologous recombination plasmids. Two vectors were transformed into S. turcica protoplasts through PEG-mediated transformation. Five StPKS down-regulated transformants and one disrupted mutant were obtained by screening of hygromycin B, PCR and RT-PCR.Comparing with the wild-type isolate, the hypae morphology of five RNAi transformants was anomalistic, including intumescent, ramose and anamorphic. The colony colour was tend to be white and melanin production was significantly declined. The deletion mutantΔStPKS didn't produce conidia. Cell wall was transparent and the hypha had no distinct septum but had lots of vacuole-like structures in cells.ΔStPKS showed an albino phenotype, the melanin content was reduced remarkably, these consistented with the results of RNAi transformants. These results indicated that the encoding products of StPKS gene was involved in DHN melanin biosynthesis, mycelial development and conidia formation.The research of pathogenic factors ofΔStPKS revealed that, wild type isolate and StPKS mutant had 5.4 MPa,4.6 MPa turgor pressure respectively. Appressorium formation ofΔStPKS was put off, the numbers of appressorium and penetration were decreased. The results showed that appressorium formation of the melanin-deficient mutants was inhibited, the low turgor pressure would affect the ability of penetration. Targeted disruption of the StPKS gene showed no affection about toxin activity, but reduced the cellulose activity, this would influenced the pathogenicity of melanin-deficient mutant.