EAGER: Engineering Decoys to Detect Pathogen Proteases and Activate Host Resistance

This project is focused on using endogenous plant genes to engineer resistance to important crop pathogens. This will be accomplished by enabling plants to detect the presence of specific pathogen proteases, which are enzymes that act like molecular scissors to cut specific target proteins in the host. Specifically, a single soybean gene will be modified, which should then enable soybean to detect the activity of pathogen proteases, and then activate defense responses. This protease recognition system does not require transfer of genes between species, thus such modified soybeans should not be considered GMOs, which should simplify regulatory approval, as well as consumer acceptance. If this approach is successful in soybean, it should be applicable to all crop plants, which would decrease our dependence on environmentally harmful pesticides, while boosting crop yields and increasing world food security.<br/><br/>Many important plant pathogens depend on proteases to infect host plants. The Innes laboratory is developing a novel method for engineering resistance to such pathogens based on detecting these specific proteases. This system arises from their work on the AvrPphB protease from the bacterium Pseudomonas syringae. AvrPphB is injected into host cells, where it targets a family of protein kinases that regulate basal defense responses, cleaving them in a single position. In Arabidopsis, this cleavage event is detected by the disease resistance (R) protein RPS5, which then activates defense responses. Specifically, cleavage of the host kinase PBS1 by AvrPphB activates RPS5-mediated resistance. The Innes laboratory has recently shown that the AvrPphB recognition sequence within PBS1 (seven amino acids) can be replaced by the recognition sequence for other pathogen proteases. These 'decoy' kinases can then be cleaved by the matching protease and activate RPS5. Thus, by manipulating the PBS1 amino acid sequence, it is possible to engineer RPS5 to recognize just about any pathogen protease. This project seeks to extend this discovery to crop plants. As a proof of concept, a soybean PBS1 ortholog will be modified, in separate constructs, to detect proteases from Soybean mosaic virus and Asian Soybean Rust. Because most soybean varieties carry an endogenous disease resistance gene that detects AvrPphB protease activity, it is expected that modification of an endogenous soybean PBS1 protein, which is highly conserved among flowering plants, will enable detection of corresponding proteases. This project will provide underrepresented minorities at the high school and undergraduate levels with opportunities to participate in hands-on research, and to engage in the topic of sustainable agriculture.