Regulation of pattern recognition receptor signalling in plants

Plants rely on a cell-autonomous innate immune system to detect the presence of microorganisms and activate immune responses that deter infection. Recognition of conserved microbial features occurs essentially at the cell surface by means of transmembrane pattern recognition receptors (PRRs).PRRs are part of multimeric protein complexes at the plasma membrane, differentially recruiting cytoplasmic kinases that connect PRR complexes to downstream signalling components.Ligand binding initiates a series of phosphorylation events within PRR complexes that activates cellular immune signalling, which includes bursts of intracellular reactive oxygen species and calcium, activation of cytoplasmic kinase cascades, and transcriptional reprogramming.As in mammals, excessive activation of plant immune responses can have detrimental consequences. Thus, a complex negative regulatory system controls different immune components to maintain cellular homeostasis.Bacterial pathogens are able to subvert the plant immune system by secreting molecules, such as effectors, that often mimic the mode-of-action of host negative regulators of immune signalling.