Recognition and Response in Plant PAMP‐Triggered Immunity


Pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI) describes the first events after pathogen invasion, whereby the plant identifies the presence of an invader and mounts a response. A race ensues in which the pathogen deploys its array of virulence molecules that act in opposition to host defence mechanisms and promote establishment of a pathogenic niche. Since the seminal work identifying the first pathogen receptor, FLAGELLIN‐SENSING 2 (FLS2), the field has worked to define receptor complexes and downstream signalling pathways. This article describes recent progress in this area. In addition, many pathogen effectors target the PTI machinery. Thus, identifying PTI components as effector targets helps to validate those molecules as components of the defence machinery. As such, early molecular interactions are key to the outcome of infection. Indeed it is thought that nonhost resistance, in which most plants species are resistant to most pathogens, is likely to be a result of the PTI system.

Key Concepts:

  • Plants have multilayered recognition systems which detect invading pathogens.

  • The first line of recognition involves detection of PAMPs via host pattern‐recognition receptors (PRRs).

  • PRRs are transmembrane receptor‐like kinases or receptor‐like proteins that perceive PAMPs at the cell surface.

  • PRRs act as a major point of control for PTI.

  • Biogenesis and localisation of PRRs to the plasma membrane requires the proteins are processed by the secretory pathway and individual PRRs have varying requirements for endoplasmic reticulum‐quality control pathways.

  • Following PAMP perception, a series of downstream defence responses results in PTI.

  • Attenuation of PRR signalling is necessary to restrict immune responses.

Keywords: disease resistance; flagellin; FLS2; PAMP‐triggered immunity; PAMP; pattern‐recognition receptor; PRR; PTI; signalling pathways

Figure 1.

The life and times of FLS2. (a) FLS2 biogenesis: (1) FLS2 is a glycosylated transmembrane protein. Transcription of FLS2 is under direct control of ethylene (ET). (2) Localisation of FLS2 to the (PM) requires that FLS2 is processed via the secretory pathway. (3) FLS2 is folded and subjected to quality control (QC) in the endoplasmic reticulum (ER), transported to the Golgi apparatus (GA) for modifications, and eventually transported to the plasma membrane , CW. (b) FLS2 reception. Prior to flagellin activation (− flagellin), FLS2 resides in a complex with the cytoplasmic protein kinase, BIK1. Following flagellin perception at the cell surface (+ flagellin), the receptor kinase BAK1 is recruited by FLS2 to form the FLS2‐BAK1 complex. Assembly of the FLS2‐BAK1 complex results in further phosphorylation events between the three kinase domains and release of the phosphorylated BIK1 from the complex. (c) FLS2 signalling: (1) Flagellin perception results in activation of (MAPK) cascades. Ligand binding also triggers a Ca2+ burst, which activates Ca2+‐dependent protein kinases (CDPKs). (2) Induction of MAPK and CDPK cascades independently induces defence gene expression. (3) FLS2 is the subject of a ubiquitination cascade leading to FLS2 degradation. Following flagellin treatment PUB12 and PUB13, two U‐box E3 ubiquitin ligases, are recruited to the FLS2 complex and phosphorylated by BAK1. PUB12 and PUB13 have auto‐ubiquitination activity and polyubiquitinate FLS2, leading to FLS2 degradation and hence downregulation. (d) Potential ET positive feedback: (1) FLS2 transcription under direct control of ethylene via binding of the transcription factors EIN3 and EIL1 to the FLS2 promoter. (2) FLS2 activation by flagellin results in ET production , thereby allowing for a positive feedback function for ethylene. BIK1 appears to be involved in ET perception.



Albrecht C, Boutrot F, Segonzac C et al. (2012) Brassinosteroids inhibit pathogen‐associated molecular pattern‐triggered immune signaling independent of the receptor kinase BAK1. Proceedings of the National Academy of Sciences of the USA 109: 303–308.

Bar M, Sharfman M, Ron M and Avni A (2010) BAK1 is required for the attenuation of ethylene‐inducing xylanase (Eix)‐induced defense responses by the decoy receptor LeEix1. Plant Journal 63: 791–800.

Boller T and Felix G (2009) A renaissance of elicitors: Perception of microbe‐associated molecular patterns and danger signals by pattern‐recognition receptors. Annual Review of Plant Biology 60: 379–406.

Boutrot F, Segonzac C, Chang KN et al. (2010) Direct transcriptional control of the Arabidopsis immune receptor FLS2 by the ethylene‐dependent transcription factors EIN3 and EIL1. Proceedings of the National Academy of Sciences of the USA 107: 14502–14507.

Bouwmeester K, de Sain M, Weide R et al. (2011) The lectin receptor kinase LecRK‐I.9 is a novel Phytophthora resistance component and a potential host target for a RXLR effector. PLos Pathogens 7: e1001327.

Brutus A, Sicilia F, Macone A, Cervone F and De Lorenzo G (2010) A domain swap approach reveals a role of the plant wall‐associated kinase 1 (WAK1) as a receptor of oligogalacturonides. Proceedings of the National Academy of Sciences of the USA 107: 9452–9457.

Chakraborty S and Newton AC (2011) Climate change, plant diseases and food security: an overview. Plant Pathology 60: 2–14.

Chinchilla D, Shan L, He P, de Vries S and Kemmerling B (2009) One for all: the receptor‐associated kinase BAK1. Trends in Plant Science 14: 535–541.

Danna CH, Millet YA, Koller T et al. (2011) The Arabidopsis flagellin receptor FLS2 mediates the perception of Xanthomonas Ax21 secreted peptides. Proceedings of the National Academy of Sciences of the USA 108: 9286–9291.

Desclos‐Theveniau M, Arnaud D, Huang TY et al. (2012) The Arabidopsis lectin receptor kinase LecRK‐V.5 represses stomatal immunity induced by Pseudomonas syringae pv. tomato DC3000. PLoS Pathogens 8: e1002513.

Dodds PN and Rathjen JP (2010) Plant immunity: towards an integrated view of plant‐pathogen interactions. Nature Reviews Genetics 11: 539–548.

Feng F, Yang F, Rong W et al. (2012) A Xanthomonas uridine 5′‐monophosphate transferase inhibits plant immune kinases. Nature 485: 114–118.

Gimenez‐Ibanez S, Ntoukakis V and Rathjen JP (2009) The LysM receptor kinase CERK1 mediates bacterial perception in Arabidopsis. Plant Signaling and Behavior 4: 539–541.

Han SW, Sriariyanun M, Lee SW et al. (2011) Small protein‐mediated quorum sensing in a gram‐negative bacterium. PLoS One 6: e29192.

Hann DR, Gimenez‐Ibanez S and Rathjen JP (2010) Bacterial virulence effectors and their activities. Current Opinion in Plant Biology 13: 388–393.

Hardham AR, Jones DA and Takemoto D (2007) Cytoskeleton and cell wall function in penetration resistance. Current Opinion in Plant Biology 10: 342–348.

Häweker H, Rips S, Koiwa H et al. (2010) Pattern recognition receptors require N‐glycosylation to mediate plant immunity. Journal of Biological Chemistry 285: 4629–4636.

Heese A, Hann DR, Gimenez‐Ibanez S et al. (2007) The receptor‐like kinase SERK3/BAK1 is a central regulator of innate immunity in plants. Proceedings of the National Academy of Sciences of the USA 104: 12217–12222.

Iizasa E, Mitsutomi M and Nagano Y (2010) Direct binding of a plant LysM receptor‐like kinase, LysM RLK1/CERK1, to Chitin in vitro. Journal of Biological Chemistry 285: 2996–3004.

Jaillais Y, Belkhadira Y, Balsemão‐Piresa E, Dangl JL and Chorya J (2011) Extracellular leucine‐rich repeats as a platform for receptor/coreceptor complex formation. Proceedings of the National Academy of Sciences of the USA 108: 8503–8507.

Jeworutzki E, Roelfsema MR, Anschütz U et al. (2010) Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca2+‐associated opening of plasma membrane anion channels. Plant Journal 62: 367–378.

Kong Q, Qu N, Gao M et al. (2012) The MEKK1‐MKK1/MKK2‐MPK4 kinase cascade negatively regulates immunity mediated by a mitogen‐activated protein kinase kinase kinase in Arabidopsis. Plant Cell 24: 2225–2236.

Korasick DA, McMichael C, Walker KA et al. (2010) Novel functions of stomatal cytokinesis‐defective 1 (SCD1) in innate immune responses against bacteria. Journal of Biological Chemistry 285: 23342–23350.

Lacombe S, Rougon‐Cardoso A, Sherwood E et al. (2010) Interfamily transfer of a plant pattern recognition receptor confers broad‐spectrum bacterial resistance. Nature Biotechnology 28: 365–369.

Laluk K, Luo H, Chai M et al. (2011) Biochemical and genetic requirements for function of the immune response regulator BOTRYTIS‐INDUCED KINASE1 in plant growth, ethylene signaling, and PAMP‐triggered immunity in Arabidopsis. Plant Cell 23: 2831–2849.

Lee H, Chah OK and Sheen J (2011) Stem‐cell‐triggered immunity through CLV3p‐FLS2 signalling. Nature 473: 376–379.

Lee SW, Han SW, Sririyanum M et al. (2009) A type I‐secreted, sulfated peptide triggers XA21‐mediated innate immunity. Science 326: 850–853.

Liu T, Liu Z, Song C et al. (2012) Chitin‐induced dimerization activates a plant immune receptor. Science 336: 1160–1164.

Lu D, Lin W, Gao X et al. (2011) Direct ubiquitination of pattern recognition receptor FLS2 attenuates plant innate immunity. Science 332: 1439–1442.

Lu D, Wu S, Gao X et al. (2010) A receptor‐like cytoplasmic kinase, BIK1, associates with a flagellin receptor complex to initiate plant innate immunity. Proceedings of the National Academy of Sciences of the USA 107: 496–501.

Mersmann S, Bourdais G, Rietz S and Robatzek S (2010) Ethylene signaling regulates accumulation of the FLS2 receptor and is required for the oxidative burst contributing to plant immunity. Plant Physiology 154: 391–400.

Monaghan J and Zipfel C (2012) Plant pattern recognition receptor complexes at the plasma membrane. Current Opinion in Plant Biology 15: 1–9.

Nicaise V, Roux M and Zipfel C (2009) Recent advances in PAMP‐triggered immunity against bacteria: Pattern recognition receptors watch over and raise the alarm. Plant Physiology 150: 1638–1647.

Petutschnig EK, Jones AM, Serazetdinova L, Lipka U and Lipka V (2010) The lysin motif receptor‐like kinase (LysM‐RLK) CERK1 is a major chitin‐binding protein in Arabidopsis thaliana and subject to chitin‐induced phosphorylation. Journal of Biological Chemistry 285: 28902–28911.

Qi Y, Tsuda K, Glazebrook J and Katagiri F (2011) Physical association of pattern‐triggered immunity (PTI) and effector‐triggered immunity (ETI) immune receptors in Arabidopsis. Molecular Plant Pathology 12: 702–708.

Roux M, Schwessinger B, Albrecht C et al. (2011) The Arabidopsis leucine‐rich repeat receptor‐like kinases BAK1/SERK3 and BKK1/SERK4 are required for innate immunity to hemibiotrophic and biotrophic pathogens. Plant Cell 23: 2440–2455.

Saijo Y (2010) ER quality control of immune receptors and regulators in plants. Cellular Microbiology 12: 716–724.

Schwessinger B, Roux M, Kadota Y et al. (2011) Phosphorylation‐dependent differential regulation of plant growth, cell death, and innate immunity by the regulatory receptor‐like kinase BAK1. PLoS Genetics 7: e1002046.

Segonzac C, Feike D, Gimenez‐Ibanez S et al. (2011) Hierarchy and roles of pathogen‐associated molecular pattern‐induced responses in Nicotiana benthamiana. Plant Physiology 156: 687–699.

Segonzac C and Zipfel C (2011) Activation of plant pattern‐recognition receptors by bacteria. Current Opinion in Microbiology 14: 54–61.

Seifert GJ and Blaukopf C (2010) Irritable walls: the plant extracellular matrix and signaling. Plant Physiology 153: 467–478.

Sharfman M, Bar M, Ehrlich M et al. (2011) Endosomal signaling of the tomato leucine‐rich repeat receptor‐like protein LeEix2. Plant Journal 68: 413–423.

Shimizu T, Nakano T, Takamizawa D et al. (2010) Two LysM receptor molecules, CEBiP and OsCERK1, cooperatively regulate chitin elicitor signaling in rice. Plant Journal 64: 204–214.

Singh P, Kuo YC, Mishra S et al. (2012) The lectin receptor kinase‐VI.2 is required for priming and positively regulates Arabidopsis pattern‐triggered immunity. Plant Cell 24: 1256–1270.

Tör M, Lotze MT and Holton N (2009) Receptor‐mediated signalling in plants: molecular patterns and programmes. Journal of Experimental Botany 60: 3645–3654.

Willmann R, Lajunen HM, Erbs G et al. (2011) Arabidopsis lysine‐motif proteins LYM1 LYM3 CERK1 mediate bacterial peptidoglycan sensing and immunity to bacterial infection. Proceedings of the National Academy of Sciences of the USA 108: 19824–19829.

Zeng W, Brutus A, Kremer JM et al. (2011) A genetic screen reveals Arabidopsis stomatal and/or apoplastic defenses against Pseudomonas syringae pv. tomato DC3000. PLoS Pathogens 7: e1002291.

Zeng W and He SY (2010) A prominent role of the flagellin receptor FLS2 in mediating stomatal response to Pseudomonas syringae pv. tomato DC3000 in Arabidopsis. Plant Physiology 153: 1188–1198.

Zhang J, Li W, Xiang T et al. (2010) Receptor‐like cytoplasmic kinases integrate signaling from multiple plant immune receptors and are targeted by a Pseudomonas syringae effector. Cell Host and Microbe 7: 290–301.

Zhang Z, Wu Y, Gao M et al. (2012) Disruption of PAMP‐induced MAP kinase cascade by a Pseudomonas syringae effector activates plant immunity mediated by the NB‐LRR Protein SUMM2. Cell Host and Microbe 11: 253–263.

Further Reading

Boller T and He SY (2009) Innate immunity in plants: an arms race between pattern recognition receptors in plants and effectors in microbial pathogens. Science 324: 742–744.

Bouwmeester K and Govers F (2009) Arabidopsis L‐type lectin receptor kinases: phylogeny, classification, and expression profiles. Journal of Experimental Botany 60: 4383–4396.

Chisholm ST, Coaker G, Day B and Staskawicz BJ (2006) Host‐microbe interactions: shaping the evolution of the plant immune response. Cell 124: 803–814.

Jones JD and Dangl JL (2006) The plant immune system. Nature 444: 323–329.

Lindeberg M, Cunnac S and Collmer A (2012) Pseudomonas syringae type III effector repertoires: last words in endless arguments. Trends in Microbiology 20: 199–208.

Ma W and Berkowitz GA (2007) The grateful dead: calcium and cell death in plant innate immunity. Cellular Microbiology 9: 2571–2585.

McDowell JM (2011) Genomes of obligate plant pathogens reveal adaptations for obligate parasitism. Proceedings of the National Academy of Sciences of the USA 108: 8921–8922.

Pedley KF and Martin GB (2005) Role of mitogen‐activated protein kinases in plant immunity. Current Opinion in Plant Biology 8: 541–547.

Pieterse CMJ, Leon‐Reyes A, Van der Ent S and Van Wees SCM (2009) Networking by small‐molecule hormones in plant immunity. Nature Chemical Biology 5: 308–316.

Thomma BPHJ, Nürnberger T and Joosten MHAJ (2011) Of PAMPs and effectors: the Blurred PTI‐ETI Dichotomy. Plant Cell 23: 4–15.

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Godfrey, Dale, and Rathjen, John P(Oct 2012) Recognition and Response in Plant PAMP‐Triggered Immunity. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0023725]