Switching on Plant Immune Signaling Systems Using Pattern Recognition Receptor Complex

Abstract

Plants are endowed with innate immune system to resist pathogen attack. Pathogen-associated molecular patterns (PAMPs) and host-associated molecular patterns (HAMPs) are danger/alarm signals to switch on the plant immune systems. Plants possess receptor systems called plant pattern recognition receptors (PRRs) for sensing pathogen- or host-derived patterns to trigger inducible immune defenses. Most of the PRRs identified are receptor-like kinases (RLKs) and receptor-like proteins (RLPs). Plants use the PRRs to defend themselves from microbial pathogens. PRRs do not act alone but rather function as part of multi-protein complexes at the plasma membrane. The PRRs interact with several transmembrane LRR receptor-like kinase proteins that act as signaling adapters or amplifiers to achieve full functionality. The PRRs are localized at the plasma membrane and the PAMPs activate expression of the genes encoding various PRRs and PRR interacting regulators to trigger defense responses against pathogens. PRRs play important role in triggering defense responses, PAMP perception by PRR is required for full immunity and plants deficient in the specific PRR become more susceptible to pathogens. However, pathogens secrete effectors, which directly target the PRRs and suppress the PRR-activated downstream immune responses. Early and robust activation of PRRs before the pathogens invade and secrete virulence effectors seems to be necessary for triggering strong defense responses and for effective management of crop diseases. Transgenic plants constitutively expressing various PRRs including FLS2, EF-Tu Receptor, XA21, and WAK1 show enhanced resistance against various fungal, oomycete, and bacterial diseases. Pathogens that are adapted to a particular host plant may be adept at suppressing the PRRs of that host by their effectors. The effectors of the pathogens might not recognize PRRs from other host plants and development of transgenic plants expressing PRRs from other plant species may provide good resistance against various pathogens. Transfer of Arabidopsis and rice PRRs to various economically important crop plants has revealed high potential of the PRRs for crop disease management. Engineering PRR-interacting protein complexes has also shown to be useful technology for crop disease management.