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Discovery of effectors in the hop downy mildew pathogen Pseudoperonospora humuli
L. M. CANO (1), S. Withers (1), D. Gent (2), N. Noel (1), L. M. Quesada-Ocampo (1). (1) North Carolina State University, Raleigh, NC, U.S.A.; (2) Oregon State University, Corvallis, OR, U.S.A.

Oomycete plant pathogens secrete effector molecules that manipulate host physiology to achieve colonization. Effector proteins have been identified in various oomycete species but little is known about the sequence, function, and evolution of effectors of downy mildew plant pathogens. <i>Pseudoperonospora humuli</i> is the causal agent of downy mildew of hop, an economically important disease that occurs worldwide and has gained importance in recent years in the United States due to an increase of hop production. The main goal of our study was to identify and make available to the oomycete community a set of candidate pathogen effectors from <i>P. humuli</i> using transcriptomics.  Identified effector candidates can be employed in high throughput functional genomics screens, commonly referred to as effectoromics, to test hop germplasm for specific pathogen recognition by resistance <i>R </i>proteins. Here we report the identification of approximately 500 sequences annotated as cytoplasmic and apoplastic effectors in <i>P. humuli</i> and discuss their potential roles in disease. Our findings are a first step toward effector-assisted breeding in hop for resistance to downy mildew.

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