The Catalase Gene MrCat1 Contributes to Oxidative Stress Tolerance, Microsclerotia Formation, and Virulence in the Entomopathogenic Fungus Metarhizium rileyi .

Catalases play a crucial role in the metabolism of reactive oxygen species (ROS) by converting H 2 O 2 into molecular oxygen and water. They also contribute to virulence and fungal responses to various stresses. Previously, the MrCat1 -deletion mutant (Δ MrCat1 ) was generated using the split-marker method in Metarhizium rileyi . In this study, the Cat1 gene was identified, and its function was evaluated. Under normal culture conditions, there were no significant differences in colony growth or dimorphic switching between Δ MrCat1 and the wild-type (WT) strains. However, under oxidative stress, the colony growth was inhibited, and the yeast-hyphal transition was suppressed in the Δ MrCat1 strain. Hyperosmotic stress did not differ significantly between the two strains. In the Δ MrCat1 strain, microsclerotia (MS) formation was delayed, resulting in less uniform MS size and a 76% decrease in MS yield compared to the WT strain. Moreover, the Δ MrCat1 strain exhibited diminished virulence. Gene expression analysis revealed up-regulation of Δ MrCat1, MrCat2 , MrCat4 , and MrAox in the Δ MrCat1 strain. These findings indicate that the MrCat1 gene in M. rileyi is essential for oxidative stress tolerance, MS formation, and virulence.