Plants are constantly exposed to would-be pathogens and pests, and thus have a sophisticated immune system to ward off these threats, which otherwise can have devastating ecological and economic ...consequences on ecosystems and agriculture. Plants employ receptor kinases (RKs) and receptor-like proteins (RLPs) as pattern recognition receptors (PRRs) to monitor their apoplastic environment and detect non-self and damaged-self patterns as signs of potential danger. Plant PRRs contribute to both basal and non-host resistances, and treatment with pathogen-/microbe-associated molecular patterns (PAMPs/MAMPs) or damage-associated molecular patterns (DAMPs) recognized by plant PRRs induces both local and systemic immunity. Here, we comprehensively review known PAMPs/DAMPs recognized by plants as well as the plant PRRs described to date. In particular, we describe the different methods that can be used to identify PAMPs/DAMPs and PRRs. Finally, we emphasize the emerging biotechnological potential use of PRRs to improve broad-spectrum, and potentially durable, disease resistance in crops.
Perception of pathogen-associated molecular patterns (PAMPs) constitutes the first layer of plant innate immunity and is referred to as PAMP-triggered immunity (PTI). For a long time, part of the ...plant community was sceptical about the importance of PAMP perception in plants. Genetic and biochemical studies have recently identified pattern-recognition receptors (PRRs) involved in the perception of bacteria, fungi and oomycetes. Interestingly, some of the structural domains present in PRRs are similar in plants and animals, suggesting convergent evolution. Lack of PAMP perception leads to enhanced disease susceptibility, demonstrating the importance of PAMP perception for immunity against pathogens in vivo . Recently, proteins with known roles in development have been shown to control immediate PRR-signalling, revealing unexpected complexity in plant signalling. Although many PAMPs recognised by plants have been described and more are likely to be discovered, the number of PRRs known currently is limited. The study of PTI is still in its infancy but constitutes a highly active and competitive field of research. New PRRs and regulators are likely to be soon identified.
► Plant PRRs are surface-localized RLKs or RLPs that form multi-protein complexes. ► The LRR-RLK BAK1 is a major regulator of several PRR-mediated pathways. ► The LysM-RLK CERK1 is part of ...multi-specificity recognition complexes. ► The cytoplasmic kinase BIK1 is a key regulator of PTI downstream of multiple PRRs. ► Phosphorylation and ubiquitination events regulate the activity of PRR complexes.
A key feature of innate immunity is the ability to recognize and respond to potential pathogens in a highly sensitive and specific manner. In plants, the activation of pattern recognition receptors (PRRs) by pathogen-associated molecular patterns (PAMPs) elicits a defense programme known as PAMP-triggered immunity (PTI). Although only a handful of PAMP-PRR pairs have been defined, all known PRRs are modular transmembrane proteins containing ligand-binding ectodomains. It is becoming clear that PRRs do not act alone but rather function as part of multi-protein complexes at the plasma membrane. Recent studies describing the molecular interactions and protein modifications that occur between PRRs and their regulatory proteins have provided important mechanistic insight into how plants avoid infection and achieve immunity.
All eukaryotic organisms have evolved sophisticated immune systems to appropriately respond to biotic stresses. In plants and animals, a key part of this immune system is pattern recognition ...receptors (PRRs). Plant PRRs are cell-surface-localized receptor kinases (RKs) or receptor proteins (RPs) that sense microbe- or self-derived molecular patterns to regulate pattern-triggered immunity (PTI), a robust form of antimicrobial immunity. Remarkable progress has been made in understanding how PRRs perceive their ligands, form active protein complexes, initiate cell signaling, and ultimately coordinate the cellular reprogramming that leads to PTI. Here, we discuss the critical roles of PRR complex formation and phosphorylation in activating PTI signaling, as well as the emerging paradigm in which receptor-like cytoplasmic kinases (RLCKs) act as executors of signaling downstream of PRR activation.
Plants possess a sophisticated multilayered immune system. DeFalco and Zipfel review the molecular mechanisms underpinning early immune signaling mediated by cell-surface pattern recognition receptors, with an emphasis on the roles of heteromeric protein complexes and phosphorylation in the activation and regulation of immune responses.
Despite being sessile organisms constantly exposed to potential pathogens and pests, plants are surprisingly resilient to infections. Plants can detect invaders via the recognition of ...pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). Plant PRRs are surface-localized receptor-like kinases, which comprise a ligand-binding ectodomain and an intracellular kinase domain, or receptor-like proteins, which do not exhibit any known intracellular signaling domain. In this review, we summarize recent discoveries that shed light on the molecular mechanisms underlying ligand perception and subsequent activation of plant PRRs. Notably, plant PRRs appear as central components of multiprotein complexes at the plasma membrane that contain additional transmembrane and cytosolic kinases required for the initiation and specificity of immune signaling. PRR complexes are under tight control by protein phosphatases, E3 ligases, and other regulatory proteins, illustrating the exquisite and complex regulation of these molecular machines whose proper activation underlines a crucial layer of plant immunity.
Plants are highly resilient to infections and detect potential invaders via the recognition of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors (PRRs). In this review, Macho and Zipfel discuss the molecular mechanisms underlying ligand perception and subsequent activation of plant PRRs.
Pathogen recognition induces the production of reactive oxygen species (ROS) by NADPH oxidases in both plants and animals. ROS have direct antimicrobial properties, but also serve as signaling ...molecules to activate further immune outputs. However, ROS production has to be tightly controlled to avoid detrimental effects on host cells, but yet must be produced in the right amount, at the right place and at the right time upon pathogen perception. Plant NADPH oxidases belong to the respiratory burst oxidase homolog (RBOH) family, which contains 10 members in the model plant Arabidopsis thaliana. The perception of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) leads to a rapid, specific and strong production of ROS, which is dependent on RBOHD. RBOHD is mainly controlled by Ca(2+) via direct binding to EF-hand motifs and phosphorylation by Ca(2+)-dependent protein kinases. Recent studies have, however, revealed a critical role for a Ca(2+)-independent regulation of RBOHD. The plasma membrane-associated cytoplasmic kinase BIK1 (BOTRYTIS-INDUCED KINASE1), which is a direct substrate of the PRR complex, directly interacts with and phosphorylates RBOHD upon PAMP perception. Impairment of these phosphorylation events completely abolishes the function of RBOHD in immunity. These results suggest that RBOHD activity is tightly controlled by multilayered regulations. In this review, we summarize recent advances in our understanding of the regulatory mechanisms controlling RBOHD activation.
Plants tailor their metabolism to environmental conditions, in part through the recognition of a wide array of self and non-self molecules. In particular, the perception of microbial or plant-derived ...molecular patterns by cell-surface-localized pattern recognition receptors (PRRs) induces pattern-triggered immunity, which includes massive transcriptional reprogramming
. An increasing number of plant PRRs and corresponding ligands are known, but whether plants tune their immune outputs to patterns of different biological origins or of different biochemical natures remains mostly unclear. Here, we performed a detailed transcriptomic analysis in an early time series focused to study rapid-signalling transcriptional outputs induced by well-characterized patterns in the model plant Arabidopsis thaliana. This revealed that the transcriptional responses to diverse patterns (independent of their origin, biochemical nature or type of PRR) are remarkably congruent. Moreover, many of the genes most rapidly and commonly upregulated by patterns are also induced by abiotic stresses, suggesting that the early transcriptional response to patterns is part of the plant general stress response (GSR). As such, plant cells' response is in the first instance mostly to danger. Notably, the genetic impairment of the GSR reduces pattern-induced antibacterial immunity, confirming the biological relevance of this initial danger response. Importantly, the definition of a small subset of 'core immunity response' genes common and specific to pattern response revealed the function of previously uncharacterized GLUTAMATE RECEPTOR-LIKE (GLR) calcium-permeable channels in immunity. This study thus illustrates general and unique properties of early immune transcriptional reprogramming and uncovers important components of plant immunity.
The first active layer of plant innate immunity relies on the recognition by surface receptors of molecules indicative of non-self or modified-self. The activation of pattern-recognition receptors ...(PRRs) by pathogen-associated molecular patterns (PAMPs) is in essence sufficient to stop pathogen invasion through transcriptional reprogramming and production of anti-microbials. The few PRR/PAMP pairs that are characterised provide useful models to study the specificity of ligand-binding and likely activation mechanisms. Both classical and new approaches are still required to identify new bacterial PAMPs. Current genetic screens, functional genomics and biochemical analyses have identified the regulation mechanisms of PRR transcription and biogenesis, provided insights into the composition of PRR complexes at the plasma membrane and highlighted the roles of long-known signalling components in PAMP-triggered immunity (PTI).
Highlights • Type-III effectors (T3Es) suppress plant immunity using multiple strategies. • PRR-triggered immunity is redundantly targeted by multiple T3Es from a single bacterial strain. • A single ...T3E can have multiple plant targets. • A given immune component can be targeted by multiple T3Es. • The study of T3Es reveals important immune components and unique biochemical processes.
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