NADPH Oxidase Regulates the Growth and Pathogenicity of Penicillium expansum

The occurrence of reactive oxygen species (ROS) during the colonization of necrotrophic pathogens attacking fruit is critical during the attack, but its importance in Penicillium expansum remains unclear. This study aimed to determine the regulatory effects of NADPH oxidase (Nox) genes on the growth and pathogenicity of P. expansum in apple fruits. Deletion mutants of Δ PeNoxA , Δ PeNoxR , and Δ PeRacA genes were constructed to determine the contribution to the colonization process. The Δ PeRacA strain had a significant effect on the reduction of growth and pathogenicity, the Δ PeNoxA strain negatively regulated the growth and development of P. expansum and did not show any significant effect on the pathogenicity, and the Δ PeNoxR strain showed no effect on the growth or pathogenicity of P. expansum in the apple fruits. However, analysis of the content of O 2 – and H 2 O 2 in the mycelium of all the Nox mutants showed a significant reduction, confirming the functionality of Nox mutations. Growth under stress conditions in the presence of Congo red, sodium lauryl sulfate, and H 2 O 2 showed a negative effect on the radial growth of Δ PeNoxA , but a positive effect on radial growth reduction by Δ PeNoxR and Δ PeRacA mutants was shown. Interestingly, the host antioxidant activity levels of superoxide dismutase (SOD) andcatalase (CAT) in the fruits after inoculation with Δ PeNoxA , Δ PeNoxR , and Δ PeRacA mutants declined, suggesting reduced ROS accumulation in the colonized region. These results suggest that PeNoxA , PeNoxR , and PeRacA differentially regulate the growth and pathogenicity of P. expansum by producing ROS, and that PeRacA showed the strongest regulatory effect.