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Barley recognition of AvrPphB suggests a programmable system for pathogen protease recognition analogous to PBS1 decoy in Arabidopsis

Morgan Carter: Cornell University

<div>Plant defense pathways crucial for disease resistance often involve host intracellular surveillance for pathogen-secreted effectors by nucleotide-binding leucine-rich repeat proteins (NLRs), some of which guard other, effector-targeted host proteins. The <em>Arabidopsis</em> guard NLR, RPS5, initiates HR when it detects cleavage of the decoy PBS1 kinase by the <em>Pseudomonas</em> effector protease AvrPphB. RPS5 can detect PBS1 cleavage even when the AvrPphB-recognition site in PBS1 is changed to that of another protease, expanding the effector recognition capacity of the NLR. Broad conservation of PBS1 in flowering plants implies that PBS1-guarding may also be conserved across species, revealing the potential to customize each plant surveillance system for key pathogens of that species. Given this rationale, our objective was to determine if barley (<em>Hordeum vulgare</em> ssp. <em>vulgare</em>) contains components of a PBS1-RPS5 surveillance system. We identified barley PBS1 homologs that are cleavable by AvrPphB and observed a range of defense responses to AvrPphB in diverse barley lines. We used lines from three families in a nested association (NAM) population to position a single significant locus on chromosome 3H associated with the AvrPphB response. This locus contains several NLR-encoding genes, including a candidate RPS5 analog that is expressed only in AvrPphB-responding lines. We are undertaking functional assays of the candidate NLR and PBS1 homologs to verify the key proteins in this response that could be modified in future work. Expanding effector recognition through gene editing <em>PBS1</em> could yield new genetic resistance for barley and other crops against pathogens that use proteases during infection.</div>