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

Summary 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 (H 2 O 2 ). Both Δ FvCP01 and Δ FvCP02 were more sensitive to H 2 O 2 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 Δ FvCP01 /Δ FvCP02 double deletion being the most sensitive to H 2 O 2 . In general, conidia were much more sensitive than agar plugs to H 2 O 2 , and conidial inoculations indicated that FvCP01 conferred more H 2 O 2 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 H 2 O 2 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 H 2 O 2 . Yet, FvCP01 was induced more than three‐fold in the Δ FvCP02 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 H 2 O 2 ‐derived oxidative stress.