|Xu, Liangsheng - Washington State University|
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2012
Publication Date: 4/5/2013
Citation: Xu, L., Chen, W. 2013. Random T-DNA mutagenesis identifies a Cu-Zn-superoxide dismutase gene as a virulence factor of Sclerotinia sclerotiorum. Molecular Plant-Microbe Interactions. 26:431-441.
Interpretive Summary: The fungal pathogen Sclerotinia sclerotiorum causes white mold disease on more than 400 plant species including grain legume crops. Managing the disease has been very challenging because of the wide host range, longevity of the pathogen in soil and lack of adequate host resistance. Further insight of the pathogenic mechanisms of the pathogen will foster developing managment strategies. This research using Agrobacterium-mediated transformation identified a Cu-Zn-superoxide dismutase gene (SsSOD1, SS1G_00699) of S. sclerotiorum as a virulence factor. Superoxide dismutase enzymes convert highly toxic superoxide to less toxic hydrogen peroxide, helping protect the pathogen from damages by reactive oxygen species generated by host plant. Mutation at this gene had no effect on growth rate and oxalic acid production in culture, but significantly reduced virulence. The function of the gene was confirmed by complementation in a yeast Saccharomyces cerevisiae mutant deficient of the Cu-Zn-superoxide dismutase. These results suggest that this Cu-Zn-superoxide dismutase gene SsSOD1 plays critical roles in detoxification of reactive oxygen species during host-pathogen interactions and is an important virulence factor of S. sclerotiorum.
Technical Abstract: Agrobacterium-mediated transformation (AMT) was used to identify potential virulence factors in Sclerotinia sclerotiorum. Screening AMT transformants identified two mutants showing significantly reduced virulence. The mutants showed similar growth rate, colony morphology, and sclerotial and oxalate production as the wild-type strain. The mutation was due to a single T-DNA insertion at 212-bp downstream of Cu-Zn-superoxide dismutase gene (SsSOD1, SS1G_00699). Expression levels of SsSOD1 were significantly increased under oxidative stresses or during plant infection in the wild type strain, but could not be detected in the mutant. SsSOD1 functionally complemented the Cu-Zn superoxide dismutase gene in a 'sod1Saccharomyces cerevisiae mutant. The SOD mutant had increased sensitivity to heavy metal toxicity and oxidative stress in culture and reduced ability to detoxify superoxide in infected leaves. The mutant also had reduced expression levels of other known pathogenicity genes endo-polygalacturanases. The function of SsSOD1 was further confirmed by SsSOD1-deletion mutation. Like AMT SOD mutant, the SsSOD1-deletion mutant exhibited similar growth rate, sensitivity to metal and oxidative stress, and reduced virulence. These results suggest that this SsSOD1 gene plays critical roles in detoxification of reactive oxygen species during host-pathogen interactions and is an important virulence factor of S. sclerotiorum.