Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 1998
Publication Date: N/A
Technical Abstract: Gibberella fujikuroi mating population A is a pathogen of maize and sorghum and produces fumonisins, a family of toxins associated with a number of mycotoxicoses. The structure of fumonisins as well as 14C-acetate feeding studies suggest that these toxins are polyketides. In order to isolate a polyketide synthase (PKS) gene involved in fumonisin biosynthesis, we employed a PCR approach which utilized a cDNA template prepared from a fumonisin-producing culture of G. fujikuroi and degenerate primers with nucleotide sequences based on the ketosynthase consensus sequence from bacterial and fungal PKSs. Analysis of the single 644 bp PCR product and flanking sequences on cosmid clones revealed the presence of a gene with a high degree of similarity to PKS1 from Cochliobolus heterostrophus and several bacterial PKS genes. Transformation of cosmid clones that include this putative PKS gene into various fumonisin producing strains of G. fujikuroi resulted in a 3 to 10 fold increase in fumonisin production compared to the untransformed progenitor strains. Transformation of a fumonisin-nonproducing (fum1-) strain with the cosmids restored wild-type fumonisin production. This suggests that either the PKS gene or another gene present on the cosmid is fum1. Transformation-mediated disruption of the native PKS gene in a wild-type G. fujikuroi strain reduced fumonisin production by over 99%. Together these results indicate that we have isolated a PKS gene that is required for fumonisin biosynthesis in G. fujikuroi.