Expansion of pathogen recognition specificity in plants using pattern recognition receptors and artificially designed decoys

Pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) are recognized by plant pattern recognition receptors (PRRs) localized on the cell surface to activate immune responses. This PAMP-triggered immunity (PTI) confers resistance to a broad range of pathogenic microbes and, therefore, has a great potential for genetically engineering broad-spectrum resistance by transferring PRRs across plant families. Pathogenic effectors secreted by phytopathogens often directly target and inhibit key components of PTI signaling pathways via diverse biochemical mechanisms. In some cases, plants have evolved to produce decoy proteins that mimic the direct virulence target, which senses the biochemical activities of pathogenic effectors. This kind of perception traps the effectors of erroneous targeting and results in the activation of effector-triggered immunity (ETI) instead of suppressing PTI. This mechanism suggests that artificially designed decoy proteins could be used to generate new recognition specificities in a particular plant. In this review, we summarize recent advances in research investigating PAMP recognition by PRRs and virulence effector surveillance by decoy proteins. Successful expansion of recognition specificities, conferred by the transgenic expression of EF-Tu receptor (EFR) and AvrPphB susceptible 1 (PBS1) decoys, has highlighted the considerable potential of PRRs and artificially designed decoys to expand plant resistance spectra and the need to further identify novel PRRs and decoys.