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Investigation of Cytochrome P450 Monooxygenases in S. homoeocarpa for Chlorothalonil Biotransformation

Abstract
Sclerotinia homoeocarpa (F.T. Bennett) is one of the most economically important pathogens on high amenity cool-season turfgrasses where it causes dollar spot. Due to decades of over-reliance and repeated chemical treatments, S. homoeocarpa has developed resistance and insensitivity to multiple classes of fungicides. To understand the genetic mechanisms of fungicide resistance, the whole genomes of two strains with varying resistance levels to fungicides, were sequenced. In unpublished data (Sang et al.), a RNA-sequencing analysis revealed three CYP450s that were validated to play a functional role in S. homoeocarpa’s resistance against different fungicide classes. We also identified CYP450 metabolic action on the multi-site mode of action fungicide chlorothalonil. Chlorothalonil is an extensively used contact fungicide and has been known to be persistent in soils. Yet, S. homoeocarpa resistance to chlorothalonil has not been reported in the field. High Performance Liquid Chromatography (HPLC) indicated faster rates of chlorothalonil biotransformation by CYP450 overexpression strains when compared to the wild-type. We show by GC-MS that the primary transformation intermediate found in soils, 4-hydroxy-2,5,6 trichloroisophthalonitrile is produced by CYP450s’ metabolism.
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