Sclerotinia sclerotiorum catalase SCAT1 affects oxidative stress tolerance, regulates ergosterol levels and controls pathogenic development

Reactive oxygen species (ROS) are essential for pathogenic development of Sclerotinia sclerotiorum. A key question for S.sclerotiorum and many other pathogens concerns how fungi tolerate/dampen the oxidative environment during growth and pathogenesis. Regulatory components of oxidative stress include both enzymatic and non-enzymatic antioxidants. Catalases are a ubiquitous family of enzymes that play an important role in the enzymatic detoxification of ROS by converting hydrogen peroxide (H₂O₂) to water and molecular oxygen. The genome of the omnivorous pathogen S.sclerotiorum contains seven predicted catalase genes. In this study we evaluate and functionally characterize the type A catalase (Scat1) in S.sclerotiorum, whose expression is highly induced during host infection. Insertional inactivation of Scat1 (δScat1) resulted in hyperbranching of hyphae accompanied by slower growth and smaller sclerotia. δScat1 strains were attenuated in pathogenicity and rendered the fungus hypersensitive to Sodium dodecyl sulfate (SDS), as well as to osmotic and salt stresses. Unexpectedly, δScat1 exhibited increased tolerance to H₂O₂, suggesting that although a member of the catalase family, generally associated with amelioration of oxidative stress, Scat1 is probably not required for detoxification of this oxygen species and presumably has different function(s). δScat1 strains had a 2-fold decrease in ergosterol content, and overall lower sterol levels compared to the wild-type strain. These observations are consistent with increased resistance to the polyene drugs amphotericin-B and nystatin. Taken together, our results suggest Scat1 is involved in modulation of ROS in a manner that deviates from the detoxification of H₂O₂, alters membrane integrity and contributes to the pathogenic success of S.sclerotiorum.