Occurrence and Mechanisms of Multidrug Resistance in Sclerotinia Homoeocarpa.

Dollar spot, the most economically significant turfgrass disease, is caused by the “sterile” ascomycete fungus Sclerotinia homoeocarpa.  Repeated fungicide applications are required throughout the growing season to maintain high turf quality on golf courses.  However, fungicide resistance has developed in at least three fungicide classes in the United States.  Cross-resistance and multiple-resistance have been documented in S. homoeocarpa. Recently multidrug resistance was conferred by resistance to multiple chemistries using the same xenobiotic detoxification mechanisms and is becoming increasingly problematic in both plant and human pathogenic fungi.  Our recent studies suggest that overexpression of ATP-binding cassette (ABC) efflux transporters and cytochrome P450 monooxygenases play in a significant role in multidrug resistance through various detoxification pathways.  Furthermore, a novel fungal specific transcription factor regulates these xenobiotic detoxification genes/proteins and has been genetically characterized in S. homoeocarpa. In addition, a gain of function mutation in the transcription factor gives constitutive overexpression of the detoxification genes/proteins resulting in resistance to xenobiotic compounds.  Current advances in understanding the genetic mechanisms of xenobiotic detoxification in S. homoeocarpa using functional genomic and genetic techniques such as RNA-seq, quantitative RT-PCR, and knockout and overexpressed mutants will be discussed.