Effector Recognition and Molecular Activation of an Arabidopsis NLR Immune Receptor Specifying Disease Resistance to Hyaloperonospora arabidopsidis

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Plants face continuous attacks by pathogenic microbes and rely on a sophisticated immune system to ward them off. Central to this immune system are intracellular resistance proteins that recognize microbe-derived effector proteins and induce physiological changes in the plant cell that ultimately lead to localized cell death and containment of the invading pathogen. This project aims at investigating in more detail one such resistance protein/effector pair RPP1/ATR1 in the model system Arabidopsis/downy mildew and to gain a better understanding of the molecular events involved in effector recognition and resistance protein activation. The investigators will use genetic and biochemical approaches to obtain definitive evidence for direct interaction between RPP1 and ATR1. Isolation of pure protein extracts of resistance proteins has been challenging, thus the investigators will employ in planta expression systems to obtain enough RPP1 protein to perform direct interaction studies with ATR1 through co-crystallization and protein pull-down experiments. Random mutagenesis of both resistance and effector proteins will provide an exhaustive map of amino acid residues that are crucial for the interaction of these proteins. Precise timing and localization of resistance proteins is imperative during an immune response. RPP1 contains signal sequences that target the protein to the nucleus and/or membrane. In this project the investigators will determine the effect of mutating these signal sequences on RPP1-mediated resistance. Finally, resistance protein activation will be studied using biochemical approaches to identify proteins associating with RPP1 prior to and upon effector recognition. Taken together, results from this project will enhance our basic understanding of plant disease resistance signaling, which may ultimately be translated into agricultural research and result in more sustainable approaches of crop protection. The project will provide training for pre- and post-doctoral fellows as well as undergraduate students.