NOXA Is Important for 's Penetration Ability and Virulence.

NADPH oxidase (Nox) genes are responsible for Reactive Oxygen Species (ROS) production in living organisms such as plants, animals, and fungi, where ROS exert different functions. ROS are critical for sexual development and cellular differentiation in fungi. In previous publications, two genes encoding thioredoxin and NADH-ubiquinone oxidoreductase involved in maintaining ROS balance were shown to be remarkably induced in a highly versus a weakly aggressive isolate. This suggested a role of these genes in the virulence of this pathogen. NoxA (NADPH oxidase A) was identified in the genome. We compared in vitro expression of in highly and weakly aggressive isolates of after elicitation with extracts from different potato tissues. expression was induced more in the weakly than highly aggressive isolate in response to leaf and stem extracts. After inoculation of potato detached leaves with these two isolates, was drastically up-regulated in the highly versus the weakly aggressive isolate. We generated single gene disruption mutants for genes. mutants had significantly reduced virulence, indicating important roles in pathogenesis on the potato. This is consistent with a significant reduction of cellophane penetration ability of the mutants compared to the wild type. However, the cell wall integrity was not impaired in the mutants when compared with the wild type. The resistance of mutants to oxidative stress were also similar to the wild type. Complementation of mutants with a full length NoxA clones restored penetration and pathogenic ability of the fungus. Our data showed that NoxA is essential for both penetration peg formation and virulence in .