Gene disruption approach to investigate the role of Fusarium graminearum and Fusarium verticillioides polygalacturonases during plant infection

Fusarium graminearum and Fusarium verticillioides are two important pathogens of cereal species, causing yield and quality losses. These fungi are known to produce polygalacturonase (PG) activity during liquid culture, but the role played by these enzymes during plant infection has not been ascertained yet. In particular, F. graminearum secretes two endo-PG isoforms, encoded by the two putative endo-pg genes contained in its genome, and F. verticillioides secretes an isoform which has been previously characterized together with its encoding gene. In order to establish the role of these PGs in pathogenesis, we have obtained by targeted homologous recombination the transformation-mediated disruption of their pg encoding genes, and the virulence of each knock-out mutant has been therefore evaluated by infecting host plants. Two different strains of F. graminearum have been transformed: preliminary infection experiments of wheat plants seem to indicate that both pg knock-out mutants maintain the capability to infect wheat, although colonization of spikes appears delayed compared to the wild-type strain. Infection experiments with the F. verticillioides pg knock-out mutant have been performed on maize seedlings and corn husks: the mutant maintains the capability to infect both tissues, but it shows a clearly evident delay in the progression of symptoms. The demonstration of the importance of F. graminearum and F. verticillioides PGs in pathogenesis might contribute to develop strategies aimed to increase the resistance of host plants to infection by these pathogens.