Dissecting oomycete-induced immunity in Arabidopsis deploying a non-toxic NEP1-like protein as PAMP

Plants have evolved various ways to defend themselves against pathogens. An important first line of defense is by recognition of conserved pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs) resulting in PAMP-triggered immunity (PTI). All plant PRRs identified so far belong to the family of receptor-like kinases (RLKs). However, for the detection of oomycetes, e.g. downy mildews and Phytophthora spp., no PRRs have been described. This project is aimed at identifying and characterizing Arabidopsis genes required for recognition of NLP, a recently identified oomycete PAMP belonging to the family of non-toxic NEP1-like proteins (NLPs) of the downy mildew Hyaloperonospora arabidopsidis. Arabidopsis responds strongly to NLPs, or fragments thereof, by mounting immunity and associated growth inhibition. These phenotypes will be used in a forward genetics approach to select decreased NLP-triggered immunity (dni) mutants. In parallel, by reverse genetics, known rlk and receptor-like protein (rlp) mutants will be screened for decreased NLP responsiveness to NLPs. The obtained mutants will be screened with other pathogens and different PAMPs to determine which processes are disturbed, and to identify oomycete-specific defects. To clone the corresponding DNI genes, whole genome sequencing of F2 plants of a selected number of dni mutants will identify the causal mutations. Functional analyses of the dni mutants and cloned DNI genes will reveal the mechanism of NLP recognition and signaling leading to immunity. Identifying an oomycete-specific PRR will provide an important missing link in the plant immune network and offers an innovative approach for disease-resistance breeding and sustainable agriculture.