Mitogen-activated protein kinases (MAPKs), are essential components of evolutionary conserved signaling pathways in eukaryotic cells. Mycosphaerella graminicola a worldwide pathogen of wheat causing Septoria tritici leaf blotch (STB), has three MAPK pathways depending respectively on kinase MgFus3, MgHog1 and MgStl2. These three signaling pathways are involved at different stages of the infection process. To decipher the infection related mechanisms controlled by these signaling pathways, we are developing a combination of molecular approaches. Comparative transcriptomics will be performed using null mutants from these three genes (MgFus3, MgHog1, MgStl2) and wild type strains with genome wide DNA microarrays grown under conditions corresponding to either an active or an inactive pathway. Additional transcriptomic analyses will rely on conditional MAPK mutants to better control the activation/inactivation status of these pathways. Genes whose expression (induction, repression) require an active MAPK will be further studied using reverse genetics and biochemistry (phosphorylation status, protein-DNA interaction).