Grapevine downy mildew, evoked by the obligate biotrophic oomycete Plasmopara viticola, is one of the most challenging diseases in viticulture. P. viticola establishes an infection by circumvention of plant immunity, which is achieved by the secretion of effector molecules. One family of potential effectors are the necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLP). NLP are most abundant in plant pathogenic microorganisms and exist in cytotoxic and non-cyctotoxic forms. Cytotoxic NLP often act as virulence factors and are synthesized in necrotrophic or hemibiotrophic pathogens during the transition from biotrophic to necrotrophic growth. In addition to these cytotoxic NLP, many non-cytotoxic NLP have been identified; their function in biotrophic pathogens is still unknown. In 2020, eight different NLP coding genes were identified in P. viticola and named PvNLP1 to PvNLP8 (Plasmopara viticolaNLP 1-8). In the present study, PvNLP4 to PvNLP8 were characterized by using qPCR analysis and transient expression in the model plant Nicotiana benthamiana. Gene expression analysis showed high PvNLP expression during the early stages of infection. Necrosis-inducing activity of PvNLP was not observed in the nonhost N. benthamiana.
Keywords: NLP; Plasmopara viticola; downy mildew; grapevine; necrosis and ethylene inducing peptide 1.