RPS5, a nucleotide-binding leucine-rich repeat (NLR) protein, is activated by the proteolytic cleavage of PBS1. Cleavage of PBS1 is carried out by the Pseudomonas syringae effector protease AvrPphB. We have shown that the cleavage site within PBS1 can be altered to contain cleavage sites for other proteases, enabling RPS5 activation by these proteases, thereby conferring resistance to different pathogens. This was exemplified by mutating PBS1 to be cleaved by the NIa protease of turnip mosaic virus (TuMV) thereby enabling RPS5 activation upon TuMV infection. However, this engineered resistance conferred a trailing necrosis phenotype indicative of an immune response too slow to contain the virus. This was overcome through the overexpression of PBS1TuMV, as this conferred complete resistance to TuMV when delivered by either Agrobacterium or by aphid transmission. These results show that RPS5-mediated defense responses are effective against bacterial and viral pathogens. This decoy approach has now been translated into soybean using endogenous PBS1 orthologs. Transgenic overexpression of this soybean PBS1 decoy conferred immunity to SMV, demonstrating that we can use endogenous PBS1 proteins in crop plants to engineer economically relevant disease resistant traits.
Coauthors: Aurelie Bak – UC Davis;Alexandra Margets – Indiana University Bloomington;Matthew Helm – Purdue University;Lucas Tang – Indiana University Bloomington;Clare Casteel – UC Davis;Roger Innes – Indiana University Bloomington