Systematic Characterization of the Kinome of Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum is one of the most important diseases on wheat and barley.  Although protein kinases are known to play major regulatory roles in fungi, systematic characterization of fungal kinomes has not been reported in plant pathogens.   The wheat scab fungus Fusarium graminearum has 116 protein kinases (PK) genes.  Although twenty of them appeared to be essential, we generated deletion mutants for the other 96 PK genes, including 12 orthologs of essential genes in yeast.  All of the PK mutants were assayed for changes in 17 phenotypes, including growth, conidiation, pathogenesis, stress responses, and sexual reproduction.  Overall, deletion of 64 PK genes resulted in at least one of the phenotypes examined, including three mutants blocked in conidiation and five mutants with increased tolerance to hyperosmotic stress.  In total, 42 PK mutants were significantly reduced in virulence or non-pathogenic, including mutants deleted of key components of the cAMP signaling and three MAPK pathways.  A number of these protein kinase genes, including two that are unique to filamentous fungi, are dispensable for hyphal growth and likely encode novel fungal virulence factors.  Ascospores play a critical role in the initiation of wheat scab.  Twenty-six PK mutants were blocked in perithecium formation or aborted in ascosporogenesis.  Additional 19 mutants were defective in ascospore release or morphology.  Interestingly, F. graminearum contains two aurora kinase genes and two CDC2 genes with distinct functions, which has not been reported in fungi.  In addition, we used the interlog approach to predict the PK-PK and PK-protein interaction networks of F. graminearum.  Several predicted interactions were verified with yeast two-hybrid or co-immunoprecipitation assays.  Protein kinase genes important for various aspects of growth, developmental, and infection processes in F. graminearum were identified in this study.