Characterization of three Fusarium graminearum overexpression mutants and their ability to elicit host defence response in cereals

Fusarium graminearum is the primary causal agent of fusarium head blight disease in cereals. With the objective of identifying pathogen-associated molecular patterns (PAMPs), three proteins were selected from the F. graminearum secretome based on their sequence homology to proteins showing pathogenicity in other plant-pathogen interactions. F. graminearum mutants were generated by overexpression (OX) or knockout (KO) of genes encoding two CFEM-domain containing proteins (FgCFEM-1 and -2) or cerato-platanin (FgCP). CFEM is a fungal-specific domain found in some membrane proteins and is thought to have roles in fungal pathogenesis. CP is a phytotoxic protein located in the fungal cell wall and is known to be involved in plant-pathogen interactions. Evaluation of the CFEM and CP mutants (OX and KO) and their ability to cause disease in wheat, barley and Brachypodium is underway. Preliminary data for the FgCFEM-1(OX) mutant, evaluated in spikes of the susceptible Canadian wheat cultivar ‘Superb’ and a moderately resistant double haploid wheat line GS-1- EM0040 (‘CIMMYT 11’/ ‘Superb’*2) shows significant reduction in aggressiveness compared with either the wild-type strain or the FgCFEM-1(KO) mutant. It is hypothesized that this F. graminearum protein is a PAMP, and that its overexpression leads to activation of PAMP-triggered immunity. To further assess the roles of these candidate PAMPs, the ability of purified FgCFEM-1, FgCFEM-2 and FgCP to induce host- defence responses is being evaluated using a combination of gene expression analysis, activity assays, and pathology tools.