Characterization of two catalase-peroxidase-encoding genes in Fusarium verticillioides reveals differential responses to in vitro versus in planta oxidative challenges

Abstract

Catalase-peroxidases (KatGs) are a superfamily of reactive oxygen species (ROS)-degrading enzymes believed to have been horizontally acquired by ancient Ascomycota from bacteria. Subsequent gene duplication resulted in two KatG paralogues in ascomycetes: the widely distributed intracellular KatG1 group and the phytopathogen-dominated extracellular KatG2 group. To functionally characterize FvCP01 (KatG1) and FvCP02 (KatG2) in the maize pathogen Fusarium verticillioides, single and double gene deletion mutants were examined in response to hydrogen peroxide (H2O2). Both ΔFvCP01 and ΔFvCP02 were more sensitive to H2O2 than the wild-type in vitro, although their sensitivity differed depending on the type of inoculum. Inoculations using mycelial agar plugs demonstrated an additive effect of the mutants, with the ΔFvCP01/ΔFvCP02 double deletion being the most sensitive to H2O2. In general, conidia were much more sensitive than agar plugs to H2O2, and conidial inoculations indicated that FvCP01 conferred more H2O2 tolerance than FvCP02. Transcriptional analysis showed the induction of FvCP01, but decreased expression of FvCP02, in both mycelia and spores in the wild-type after H2O2 exposure, but this trend was reversed when the fungus was grown on germinating maize seeds. This interaction with the plant increased the expression of FvCP02, but not FvCP01, indicating that FvCP02 may be responsive to plant-derived H2O2. Yet, FvCP01 was induced more than three-fold in the ΔFvCP02 mutant grown on germlings, suggesting that FvCP01 can compensate for the loss of FvCP02. Given the differential responses of these two F. verticillioides genes to in vitro versus in planta challenges, a model is proposed to illustrate the differing roles of FvCP01 and FvCP02 in protective responses against H2O2-derived oxidative stress.