Plants have evolved a robust innate immune system that recognizes pathogen molecules and then activates defense. Immunity involves both cell surface receptors, often transmembrane protein kinases, and intracellular NLR immune receptors, often encoded by Resistance (R) genes. NLRs are modular proteins with an N-terminal signaling domain, a nucleotide-binding domain and C-terminal LRRs. NLRs either directly or indirectly recognize pathogen effector molecules. Plants show extensive within- and between-species diversity in their NLR-encoding repertoires, which we investigate using sequence capture; polymorphism in NLR repertoires is important for their efficacy. We apply these methods to recruit and deploy multiple genes for resistance to potato late blight caused by Phytophthora infestans.
Some resistances require two NLR proteins. One (the sensor) detects effector action, while the other (helper) NLR transduces the signal. Arabidopsis RPS4 and RRS1 genes, encoding NLR proteins, confer recognition of AvrRps4 or PopP2 bacterial effectors. RRS1 carries a C- terminal WRKY transcription factor domain targeted by AvrRps4 and PopP2, suggesting these effectors target other WRKY proteins. I will provide updates on how the RPS4/ RRS1 complex detects these effectors and then activates defense upon effector recognition.