Functional analysis of catalase-peroxidase encoding genes in the fungal wheat pathogen Zymoseptoria tritici

Zymoseptoria tritici is the new name of the foliar wheat pathogen cereal Mycosphaerella graminicola (teleomorph)/Septoria tritici (anamorph) that causes septoria tritici blotch particularly in regions with high rainfall and moderate temperatures during the production season. Similar to many plant pathogens, Z. tritici possesses three catalase-peroxidase genes that are known to detoxify H2O2 accumulated in the foliage during colonization. In the current study, we functionally analysed these three catalase-peroxidase genes and found that MgCatD-1, encoding a secreted catalase-peroxidase, plays an important role in the pathogenicity of Z. tritici. MgDCat-1 mutants hardly induced any disease symptoms and expression analysis of MgDCat-1 in planta revealed that it is up-regulated during pathogenesis, particularly at 8 dpi (days post inoculation). This coincides with an important switch from a biotrophic to a necrotrophic lifestyle during pathogenesis suggesting that this gene is likely required to overcome H2O2-dependant defence responses during colonization. Furthermore, the MgDCat-1 strain is hypersensitive to H2O2 as the spore germination dropped to 50% at 4mM H2O2 and to complete inhibition at 6 mM H2O2 compared to the WT IPO323 strain. These results show that secreted catalase-peroxidase is an important pathogenicity factor for successful pathogenesis of Z. tritici.