A pectin methyl esterase is a virulence factor of Fusarium gramminearum when infecting both common and durum wheat.

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most dangerous disease of wheat crops worldwide. Trichothecene toxins are virulence factors during spike infection and degradation of plant cell wall components are visible at early stages of infection. In order to understand the contribution of cell wall degrading enzymes (CWDEs) to virulence, we are following two approaches: the production of deletion mutants of some fungal CWDEs, and the production of transgenic wheat plants expressing inhibitors of CWDEs. By these approaches we obtained some fungal mutants knocked out for pectin methyl esterase (PME) activity and, on the other side, transgenic durum wheat plants expressing a PME inhibitor (PMEI) able to reduce the plant PME activity and to increase the methylesterification degree of cell wall pectins . Infection experiments of wheat spikes showed that the fungal PME deletion mutants are less virulent than the wild type strain on both common and durum wheat. Transgenic durum wheat expressing PMEI showed an increase of resistance when infected with wild type F. graminearum but no further increase of resistance was observed when the transgenic plants were inoculated with the fungal mutants. These results clearly indicate a contribution of PME to virulence of F. graminearum and that methylesterification of pectin in the wheat cell wall play a role in contrasting the infection of F. graminearum.