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Mining the Penicillium expansum proteome to unlock fungal virulence mechanisms during postharvest apple fruit decay

Wayne Jurick II: USDA-ARS Food Quality Laboratory

<div>The blue mold fungus, <em>Penicillium expansum, </em>is one of the most globally important postharvest pathogens. The fungus reduces fruit quality, produces harmful mycotoxins, and contributes to food waste. It is a successful saprophyte, and is an aggressive necrotrophic wound pathogen that utilizes complex biochemical processes to overcome the host. To better understand fundamental mechanisms of <em>P. expansum </em>virulence, we compared the proteomes of an aggressive, wild-type strain (R19) and a lesser virulent mutant with a T-DNA insertion in the Heat Shock Protein 60 gene (HSP60). Proteins were extracted from mycelia, and peptides were labeled with isobaric tandem mass tags and analyzed by mass spectrometry. More than 3,500 proteins were quantified and mapped to known biochemical pathways in KEGG. In addition, proteins released into the culture medium were separately purified and analyzed. These included at least 100 secreted proteins (i.e. CAZymes) such as aspartic proteases, glucanases, invertases, and pectate lyases. It is likely that these enzymes contribute to decay by digesting host proteins and complex carbohydrates in apple. This study is the most detailed proteomic evaluation of this pathogen to date, and the results will provide a deeper understanding of how this pathogen causes disease. Our end goal is to translate these findings into new controls by interfering with fungal pathways, effectors and processes vital for blue mold decay development during storage.</div>