Molecular mechanisms of toxin-induced susceptibility and plant immunity-Functional diversification within the microbial NLP superfamily

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Host leaf necrosis and ethylene-inducing peptide 1-like proteins (NLP) are produced by plant pathogenic species from three microbial lineages; bacteria, fungi and oomycetes. Many NLPs are pore-forming toxins that facilitate infection of eudicot plants upon binding to eudicot-specific glycosphingolipid toxin receptors. Identification of NLP proteins lacking cytolytic activities suggests functional diversification within this microbial superfamily. Expression patterns of genes encoding non-cytolytic NLPs (ncNLPs) and tertiary structure similarities of ncNLPs with fungal lectins suggest that these proteins may play roles in host attachment at early phases of host infection. However, no evidence is available for a role of ncNLPs as microbial virulence factors. Here, we propose to conduct a comprehensive analysis of the putative disease-promoting activities of twelve ncNLPs from four different microbial species by transient expression in Nicotiana benthamiana and subsequent infection with Phytophthora infestans. We further attempt to study a proposed role of ncNLPs as lectin-like molecules during early host infection, and to identify host target structures for ncNLPs. In addition, we devise a strategy to control parasitic plant infestation in solanaceous plants by conditional, infection site-specific expression of a cytolytic NLP.