A Fusarium graminearum polygalacturonase gene is required for full virulence during wheat infection

Fusarium graminearum is the main causal agent of Fusarium head blight (FHB) in cereals. In wheat, FHB causes remarkable yield and quality losses because of mycotoxins accumulation in the infected kernels. F. graminearum is known to produce two endo-polygalacturonases (PGs) in liquid culture and during infection of wheat plants. The role played by these PGs during the infection process has not been ascertained yet and it has been often neglected because graminaceous plant tissues have a cell wall consisting mainly of cellulose and xylan. In order to establish the role of these PGs in pathogenesis, we have disrupted by targeted homologous recombination the pg encoding genes of this fungus. When grown in liquid culture containing pectin as the sole carbon source, the PG activity produced by the \u394PG1 mutant resulted negligible compared to that produced by wild-type and \u394PG2 mutant strains; however, the dry weight of wild-type and of both mutant strains was comparable. The virulence of each mutant has been evaluated by infecting wheat plants: results indicate that both pg knock-out mutants maintain the capability to infect wheat, although the \u394PG1 mutant shows a significant reduction of virulence compared to the wild-type strain (about 50% less infected spikelets), while no reduction of virulence is observed with the \u394PG2 mutant. Therefore, PG1 can be considered a virulence factor of F. graminearum during spike infection