The Gpmk1 MAP kinase of Fusarium graminearum regulates the induction of specific secreted enzymes

Recently, we described Gpmk1 MAP kinase-disruption mutants of Fusarium graminearum that were fully viable in vitro, but had completely lost their ability to infect wheat. As cell wall-degrading enzymes are postulated to participate in the infection process of F. graminearum, these MAP kinase-disruption mutants were analysed for their ability to produce cell wall-degrading enzymes in vitro and compared with the wild-type strain. The gpmk1 disruption had no effect on the production of pectinolytic or amylolytic enzymes. However, Gpmk1 regulates the early induction of extracellular endoglucanase, xylanolytic, and proteolytic activities. Furthermore, the MAP kinase was responsible for the overall induction of secreted lipolytic activities. Since the disruption of the Gpmk1 MAP kinase leads to an apathogenic phenotype, these results suggest that the infection process of F. graminearum depends on the secretion of cell wall-degrading enzymes, particularly during the early infection stage. Finally, this work provides the first detailed analysis of the apathogenic phenotype of the F. graminearum Gpmk1 mutants.