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SPECIAL SESSION: 18th I. E. Melhus Graduate Student Symposium: Molecular Basis of Plants, Pathogens, And Plant-Microbe Interactions: Today’s Students Build The Foundation for Next Level Plant Disease Resistance

Arabidopsis and barley convergently evolved an engineerable pathogen protease detection mechanism
Morgan Carter - Cornell University. Roger Innes- Indiana University, Roger Wise- USDA-Agricultural Research Service, Ana Maria Restrepo Sierra- Cornell University, Adam Bogdanove- Cornell University, Matthew Helm- Indiana University, Antony Chapman- Iowa State University, Emily Wan- Cornell

Engineering known resistance mechanisms is a valuable approach to combatting plant disease. While modifying NLRs (nucleotide binding leucine rich repeat) that mediate effector triggered immunity is difficult, we can modify NLR-guarded host proteins to alter their specificity. The Pseudomonas syringae protease effector AvrPphB activates the Arabidopsis NLR RPS5 by cleaving a decoy kinase, PBS1. By exchanging the AvrPphB cleavage site for that of a viral protease, PBS1 can confer resistance to the virus instead of P. syringae. Because PBS1-like kinases are highly conserved and involved in pattern triggered immunity, we hypothesized that the RPS5-PBS1 guard-decoy system would be present in other plants. We found that wheat and barley lines respond to AvrPphB with chlorosis or necrosis. In a genome wide association study of barley, we mapped the response to a single locus with an NLR gene (AvrPphB Response 1; Pbr1) that has expression and sequence polymorphism across barley genotypes correlated with AvrPphB response. PBR1 is phylogenetically distant from RPS5, but triggers an HR when transiently expressed in Nicotiana benthamiana with AvrPphB. We identified barley PBS1 homologs and showed that they are cleaved by AvrPphB and co-immunoprecipitate with PBR1 in planta. We conclude that barley and Arabidopsis convergently evolved NLRs to guard PBS1 kinases. These results suggest that PBS1-based decoy engineering could be deployed in small grain crops like barley and wheat.