FLS2

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LRR receptor-like serine/threonine-protein kinase FLS2
Crystal structure of the extracellular domains of FLS2 and BAK1 from Arabidopsis thaliana , in complex with the bacterial flagellin epitope flg22 ( PDB: 4MN8 ​) [1]
Identifiers
Organism Arabidopsis thaliana
SymbolFLS2
UniProt Q9FL28
Search for
Structures Swiss-model
Domains InterPro

FLS genes have been discovered to be involved in flagellin reception of bacteria. FLS1 was the original gene discovered shown to correspond with a specific ecotype within Arabidopsis thaliana . Even so, further studies have shown a second FLS gene known as FLS2 that is also associated with flagellin reception. FLS2 and FLS1 are different genes with different responsibilities, but are related genetically. FLS2 has a specific focus in plant defense and is involved in promoting the MAP kinase cascade. Mutations in the FLS2 gene can cause bacterial infection by lack of response to flg22. Therefore,FLS2’s primary focus is association with flg22 while its secondary focus is the involvement of promoting the MAP kinase cascade in plant defense. [2]

Contents

FLS2 and its similarities to receptor-like kinases

FLS2 is considered a receptor-like kinase (RLK). RLKs are essentially tyrosine kinases fused to an N-terminal leucine-rich repeat domain, which controls its function. Although tyrosine kinases are widespread and present in mammals, this type of fusion is only found in plants. RLKs are transmembrane proteins that consists of inner, outer, and central membrane regions.[ clarification needed ] RLKs play an important role in plant reception which will be shown through FLS2. [3] BRASSINOSTEROID INSENSITIVE 1 (BRI1) is another important RLK with a lot of similarities to FLS2. Despite sharing many of the same signalling components, FLS2 and BRI1 have very different effects on the cell. [4]

Structure

FLS2 consists of 3 domains: an extracellular, a transmembrane, and an intracellular. The extracellular domain is known as the Leucine-rich repeat (LRR) domain. It is in this region, which is the amino-terminus, where it is said to have direct interaction with flagellin initiating the response of FLS2 to flg22. The transmembrane domain is where proteins transition from extracellular to intracellular. This region is usually very thermodynamically stable and occurs only in the phospholipid membrane between cells. The intracellular domain is the serine/threonine kinase domain. In this domain, phosphorylation catalyzes a protein kinase cascade leading to a response. [5] In FLS2, this response elicits changes in growth and plant defenses. [6]

Ectopic expression

One experiment performed to show involvement of FLS2 in flagellin perception was an ectopic expression of FLS2 using the CaMV 35S gene promoter in one wild type Arabidopsis thaliana plant and two supposed mutant Arabidopsis thaliana plants. The wild type Arabidopsis plant was indicated by Col-0 and the two mutants were indicated by 35S::FLS2-col2 and 35S::FLS2-col4. In this experiment, callose deposition and production of active oxygen species were the variables considered to show flagellin perception after treatment of flg22 as indicated by previous research (Gomez-Gomez, et al. 1999). Results for this study showed a few things. The first thing it showed was a response in callose deposition 12 hours after treatment in only one plant type which was the mutant 35S::FLS2-col2. In the wild type and mutant 35S::FLS2-col4, no callose deposition was detected in plants that exhibited reduced levels of FLS2. In direct correlation to the callose deposition response, the second thing observed was a luminol-based assay to show oxidative burst in leaf tissues of the three plants types. The luminol-based assay showed a rapid and strong oxidative response in mutant 35S::FLS2-col2 with treatment of 10nM flg22, whereas a 10nM treatment of flg22 in the mutant 35S::FLS2-col4 was unable to induce any oxidative response that would occur naturally in the wild type Arabidopsis plant. Even so, higher treatment levels of flg22 would elicit an oxidative response but not significant compared to the wild type. The last thing observed in this experiment was treatment of flg22 in regards to growth inhibition to T2 seedlings. Growth inhibition in 35S::FLS2-col2 was greater than the wild type under flg22 treatment, whereas 35S::FLS2-col4 showed a reduced growth inhibition compared to wild type plants under flg22 treatment which is inverse of the oxidative response in these two mutants relative to the wild type. [2]

Involvement in defense responses

In the same way that mammals and insects have an innate immunity response to pathogens, plants have a defense system that is similar yet modified. The biggest difference between plants, mammals, and insects is that mammals and insects are not stationary like plants, therefore a plant’s defense system is more complex and more reliant of signaling pathways to notify the plant of what could be potentially attacking. With that in mind, it is important that all gram positive and gram negative bacteria share flagellin. With plants being stationary, a specific molecular pattern of flagellin can be recognized by plants to determine phytopathogenic bacteria in plant defense. As discovered by the ectopic expression of FLS2 study, [2] FLS2 is directed related to flagellin perception, so by discovery and by natural way of the plant, FLS2 is the gene responsible for perception of flagellin which signals a plant defense response. Things are not all settled here because, as mentioned earlier, gram positive and gram negative bacteria share flagellin which means that plants cannot distinguish between avirulent and virulent bacteria. This could provide extremely useful when an abundance of pathogenic bacteria are present, however this can also prove inefficient when plant defense response is occurring due to flagellin perception of avirulent bacteria, or so one would think. In actuality, avirulent bacteria defense responses are higher than virulent bacteria defense response due to the presence of multiple specific elicitors. Hutcheson (1997) [7] found that the tertiary and quaternary structures of protein elicitors are dependent on elicitor activity. Even so, resistant gene products are commonly found in Leucine rich repeat domains which is the extracellular domain of FLS2, and hrp genes are directly related to disease incitement and hypersensitive response to resistant plants. In short, the more elicitors that are present within flagellin perception, the more plant defense response will occur regardless of virulence. It is just more common for avirulent pathogen to produce more elicitors. [2]

Expression in tomato cells

The design of this experiment is similar to previous literature from [2] and [8] but unlike those two publications, in this publication, [3] the promoter used was the 35S cauliflower mosaic virus promoter used to express FLS2 coding sequences fused to a triple c-myc tag. What happens to a FLS2 gene in Arabidopsis is known but this study looks at how the FLS2 gene in Arabidopsis may affect a plant that contains a FLS2 gene that does not respond similarly to Arabidopsis. Figure 1 in [3] shows how tomato cells with no introduction to an Arabidopsis FLS2 gene show no response to the perception of either flg15 or flg22. However, when viewing the ArabidopsisFLS2 gene and the tomato cells with the Arabidopsis FLS2 gene added, it is clear that the responses are similar due to the presence of the ArabidopsisFLS2 gene. [3]

Alkalinization response induced by the flagellin derivative flg22-ΔA16/17

Alkalinization has been used to show ion fluxes across membranes in previous literature. [9] [10] [11] In this study, alkalinization induced by the flagellin derivative flg22-ΔA16/17 in tomato plants expressing the Arabidopsis FLS2 gene. Extracellular alkalinization was used to elicit a response in these type plants. Alkalinization had no effect on non-treated tomato plants, but increased binding activity to FLS2 was shown with no increase in sensitivity toward flg22 in the tomato plants expressing the ArabidopsisFLS2 gene. This lack of increase in sensitivity could be attributed to a number of factors that are unknown, yet hypothesized. Even so, the binding of tomato plants expressing ArabidopsisFLS2 gene showed similar sensitivity of flg15 to that of normal tomato plants. This indicates that both the Arabidopsis FLS2 gene and the tomato plant FLS2 gene are both working in tomato plants expressing ArabidopsisFLS2 gene. The Arabidopsis FLS2 gene responds to flg22 and the natural tomato FLS2 gene responds to flg15. Furthermore, the tomato FLS2 gene was analyzed for any derivatives that might be responsible for gene expression. Although less active than flg22, its derivative flg22-ΔA16/17 was found to elicit a medium alkalinization response in Arabidopsis FLS2 gene in both Arabipdopsis and tomato plants expressing ArabidopsisFLS2 gene. Essentially, the majority of flagellin perception occurring in tomato plants expressing ArabidopsisFLS2 gene is occurring because of the ArabidopsisFLS2 gene while a minor portion of flagellin perception can be attributed to the tomato FLS2 gene. [3]

Related Research Articles

<i>Arabidopsis thaliana</i> Model plant species in the family Brassicaceae

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally considered a weed.

<span class="mw-page-title-main">Flagellin</span> Bacterial protein

Flagellin is a globular protein that arranges itself in a hollow cylinder to form the filament in a bacterial flagellum. It has a mass of about 30,000 to 60,000 daltons. Flagellin is the principal component of bacterial flagella, and is present in large amounts on nearly all flagellated bacteria.

<span class="mw-page-title-main">Jasmonate</span> Lipid-based plant hormones

Jasmonate (JA) and its derivatives are lipid-based plant hormones that regulate a wide range of processes in plants, ranging from growth and photosynthesis to reproductive development. In particular, JAs are critical for plant defense against herbivory and plant responses to poor environmental conditions and other kinds of abiotic and biotic challenges. Some JAs can also be released as volatile organic compounds (VOCs) to permit communication between plants in anticipation of mutual dangers.

Pattern recognition receptors (PRRs) play a crucial role in the proper function of the innate immune system. PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. They are proteins expressed mainly by cells of the innate immune system, such as dendritic cells, macrophages, monocytes, neutrophils, as well as by epithelial cells, to identify two classes of molecules: pathogen-associated molecular patterns (PAMPs), which are associated with microbial pathogens, and damage-associated molecular patterns (DAMPs), which are associated with components of host's cells that are released during cell damage or death. They are also called primitive pattern recognition receptors because they evolved before other parts of the immune system, particularly before adaptive immunity. PRRs also mediate the initiation of antigen-specific adaptive immune response and release of inflammatory cytokines.

<span class="mw-page-title-main">Innate immune system</span> One of the two main immunity strategies

The innate, or nonspecific, immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, insects, and primitive multicellular organisms.

Systemic acquired resistance (SAR) is a "whole-plant" resistance response that occurs following an earlier localized exposure to a pathogen. SAR is analogous to the innate immune system found in animals, and although there are many shared aspects between the two systems, it is thought to be a result of convergent evolution. The systemic acquired resistance response is dependent on the plant hormone, salicylic acid.

<span class="mw-page-title-main">Systemin</span> Plant peptide hormone

Systemin is a plant peptide hormone involved in the wound response in the family Solanaceae. It was the first plant hormone that was proven to be a peptide having been isolated from tomato leaves in 1991 by a group led by Clarence A. Ryan. Since then, other peptides with similar functions have been identified in tomato and outside of the Solanaceae. Hydroxyproline-rich glycopeptides were found in tobacco in 2001 and AtPeps were found in Arabidopsis thaliana in 2006. Their precursors are found both in the cytoplasm and cell walls of plant cells, upon insect damage, the precursors are processed to produce one or more mature peptides. The receptor for systemin was first thought to be the same as the brassinolide receptor but this is now uncertain. The signal transduction processes that occur after the peptides bind are similar to the cytokine-mediated inflammatory immune response in animals. Early experiments showed that systemin travelled around the plant after insects had damaged the plant, activating systemic acquired resistance, now it is thought that it increases the production of jasmonic acid causing the same result. The main function of systemins is to coordinate defensive responses against insect herbivores but they also affect plant development. Systemin induces the production of protease inhibitors which protect against insect herbivores, other peptides activate defensins and modify root growth. They have also been shown to affect plants' responses to salt stress and UV radiation. AtPEPs have been shown to affect resistance against oomycetes and may allow A. thaliana to distinguish between different pathogens. In Nicotiana attenuata, some of the peptides have stopped being involved in defensive roles and instead affect flower morphology.

The gene-for-gene relationship is a concept in plant pathology that plants and their diseases each have single genes that interact with each other during an infection. It was proposed by Harold Henry Flor who was working with rust (Melampsora lini) of flax (Linum usitatissimum). Flor showed that the inheritance of both resistance in the host and parasite ability to cause disease is controlled by pairs of matching genes. One is a plant gene called the resistance (R) gene. The other is a parasite gene called the avirulence (Avr) gene. Plants producing a specific R gene product are resistant towards a pathogen that produces the corresponding Avr gene product. Gene-for-gene relationships are a widespread and very important aspect of plant disease resistance. Another example can be seen with Lactuca serriola versus Bremia lactucae.

<span class="mw-page-title-main">Integrin-linked kinase</span> Protein-coding gene in the species Homo sapiens

Integrin-linked kinase is an enzyme that in humans is encoded by the ILK gene involved with integrin-mediated signal transduction. Mutations in ILK are associated with cardiomyopathies. It is a 59kDa protein originally identified in a yeast-two hybrid screen with integrin β1 as the bait protein. Since its discovery, ILK has been associated with multiple cellular functions including cell migration, proliferation, and adhesion.

<span class="mw-page-title-main">Wall-associated kinase</span>

Wall-associated kinases (WAKs) are one of many classes of plant proteins known to serve as a medium between the extracellular matrix (ECM) and cytoplasm of cell walls. They are serine-threonine kinases that contain epidermal growth factor (EGF) repeats, a cytoplasmic kinase and are located in the cell walls. They provide a linkage between the inner and outer surroundings of cell walls. WAKs are under a group of receptor-like kinases (RLK) that are actively involved in sensory and signal transduction pathways especially in response to foreign attacks by pathogens and in cell development. On the other hand, pectins are an abundant group of complex carbohydrates present in the primary cell wall that play roles in cell growth and development, protection, plant structure and water holding capacity.

Peptide signaling plays a significant role in various aspects of plant growth and development and specific receptors for various peptides have been identified as being membrane-localized receptor kinases, the largest family of receptor-like molecules in plants. Signaling peptides include members of the following protein families.

Resistance genes (R-Genes) are genes in plant genomes that convey plant disease resistance against pathogens by producing R proteins. The main class of R-genes consist of a nucleotide binding domain (NB) and a leucine rich repeat (LRR) domain(s) and are often referred to as (NB-LRR) R-genes or NLRs. Generally, the NB domain binds either ATP/ADP or GTP/GDP. The LRR domain is often involved in protein-protein interactions as well as ligand binding. NB-LRR R-genes can be further subdivided into toll interleukin 1 receptor (TIR-NB-LRR) and coiled-coil (CC-NB-LRR).

BRI1-associated receptor kinase 1 is an important plant protein that has diverse functions in plant development.

<span class="mw-page-title-main">DORN1</span>

DORN1 refers to a purinergic receptor found in green plants, which is involved in extracellular ATP detection. Through the process of signal transduction, DORN1 couples extracellular ATP binding to downstream signalling and ultimately gene expression, which is thought to aid in plant survival.

Mitogen-activated protein kinase (MAPK) networks are the pathways and signaling of MAPK, which is a protein kinase that consists of amino acids serine and threonine. MAPK pathways have both a positive and negative regulation in plants. A positive regulation of MAPK networks is to help in assisting with stresses from the environment. A negative regulation of MAPK networks is pertaining to a high quantity of reactive oxygen species (ROS) in the plant.

<span class="mw-page-title-main">Leucine-rich repeat receptor like protein kinase</span>

Leucine-rich repeat receptor like protein kinase are plant cell membrane localized Leucine-rich repeat (LRR) receptor kinase that play critical roles in plant innate immunity. Plants have evolved intricate immunity mechanism to combat against pathogen infection by recognizing Pathogen Associated Molecular Patterns (PAMP) and endogenous Damage Associated Molecular Patterns (DAMP). PEPR 1 considered as the first known DAMP receptor of Arabidopsis.

Theseus1 (THE1) is a transmembrane receptor-like kinase (RLK) that is found in plant cells. It was originally discovered in Arabidopsis thaliana as part of a family of 17 related proteins, commonly referred to as the Theseus1/Feronia family or the CrRLK family. So far, THE1 and 5 other members in the same family of RLKs have been found to play key roles in cell elongation during vegetative growth through interacting mostly with the cell wall. Though the exact mechanism for this process is still unknown, it is thought to be very similar to, and even partially regulated by, the brassinosteroid pathway. In addition, Theseus1 has the ability to detect changes in cell wall integrity and could possibly even recognize pathogenic sequences. While the workings of THE1 and other members of the CrRLK family are understood on a general level, research of the specific interactions between them has yet to be published.

<span class="mw-page-title-main">EF-Tu receptor</span> Pattern-recognition receptor (PRR)

EF-Tu receptor, abbreviated as EFR, is a pattern-recognition receptor (PRR) that binds to the prokaryotic protein EF-Tu in Arabidopsis thaliana. This receptor is an important part of the plant immune system as it allows the plant cells to recognize and bind to EF-Tu, preventing genetic transformation by and protein synthesis in pathogens such as Agrobacterium.

Botrytis–induced kinase 1 (BIK1) is a membrane-anchored enzyme in plants. It is a kinase that provides resistance to necrotrophic and biotrophic pathogens. As its name suggests, BIK1 is only active after being induced by Botrytis infection. When Botrytis cinerea is present, the BIK1 gene is transcribed so that the kinase is present to defend the cell. BIK1 functions to regulate the amount of salicylic acid (SA) present in the cell. When Botrytis cinerea or Alternaria brassicicola or any other necrotrophic pathogen is present, BIK1 is transcribed to regulate the pathogen response mechanisms. When BIK1 is present, SA levels decrease, allowing the nectrotrophic response to take place. When nectrotrophic pathogens are not present, BIK1 is not transcribed and SA levels increase, limiting the necrotrophic resistance pathway. Only the pathogenic defense response that is initiated by BIK1 is dependent on SA levels. Non-pathogenic cellular functions occur independently. In terms of non-pathogenic cellular functions, BIK1 is described as a critical component of ET signaling and PAMP-triggered immunity to pathogens.

<span class="mw-page-title-main">Brassinosteroid insensitive-1</span>

Brassinosteroid insensitive 1 (BRI1) is the major receptor of the plant hormone brassinosteroid. It plays very important roles in plant development, especially in the control of cell elongation and for the tolerance of environmental stresses. BRI1 enhances cell elongation, promotes pollen development, controls vasculature development and promotes chilling and freezing tolerance. BRI1 is one of the most well studied hormone receptors and it acts a model for the study of membrane-bound receptors in plants.

References

  1. ↑ Sun, Yadong; Li, Lei; Macho, Alberto P.; Han, Zhifu; Hu, Zehan; Zipfel, Cyril; Zhou, Jian-Min; Chai, Jijie (November 2013). "Structural Basis for flg22-Induced Activation of the Arabidopsis FLS2-BAK1 Immune Complex". Science. 342 (6158): 624–628. Bibcode:2013Sci...342..624S. doi:10.1126/science.1243825. ISSN   0036-8075. PMID   24114786. S2CID   206551534.
  2. 1 2 3 4 5 Gómez-Gómez, Lourdes; Boller, Thomas (2000-06-01). "FLS2: An LRR Receptor–like Kinase Involved in the Perception of the Bacterial Elicitor Flagellin in Arabidopsis". Molecular Cell. 5 (6): 1003–1011. doi: 10.1016/S1097-2765(00)80265-8 . PMID   10911994.
  3. 1 2 3 4 5 Chinchilla, Delphine; Bauer, Zsuzsa; Regenass, Martin; Boller, Thomas; Felix, Georg (2006-02-01). "The Arabidopsis Receptor Kinase FLS2 Binds flg22 and Determines the Specificity of Flagellin Perception". The Plant Cell. 18 (2): 465–476. doi:10.1105/tpc.105.036574. ISSN   1040-4651. PMC   1356552 . PMID   16377758.
  4. ↑ Bücherl, Christoph A; Jarsch, Iris K; Schudoma, Christian; Segonzac, Cécile; Mbengue, Malick; Robatzek, Silke; MacLean, Daniel; Ott, Thomas; Zipfel, Cyril (2017-03-06). "Plant immune and growth receptors share common signalling components but localise to distinct plasma membrane nanodomains". eLife. 6. doi: 10.7554/eLife.25114 . ISSN   2050-084X. PMC   5383397 . PMID   28262094.
  5. ↑ Shiu, S.H., and Bleecker, A.B. (2001). Plant receptor-like kinase gene family: Diversity, function, and signaling. Sci. STKE 2001, RE22.
  6. ↑ Gómez-Gómez, Lourdes; Felix, Georg; Boller, Thomas (1999-05-01). "A single locus determines sensitivity to bacterial flagellin in Arabidopsis thaliana". The Plant Journal. 18 (3): 277–284. doi: 10.1046/j.1365-313X.1999.00451.x . ISSN   1365-313X. PMID   10377993.
  7. ↑ Hutcheson, Steven W. (1998). "Current Concepts of Active Defense in Plants". Annual Review of Phytopathology. 36 (1): 59–90. doi:10.1146/annurev.phyto.36.1.59. PMID   15012493.
  8. ↑ Zipfel, Cyril; Robatzek, Silke; Navarro, Lionel; Oakeley, Edward J.; Jones, Jonathan D. G.; Felix, Georg; Boller, Thomas (2004-04-15). "Bacterial disease resistance in Arabidopsis through flagellin perception". Nature. 428 (6984): 764–767. Bibcode:2004Natur.428..764Z. doi:10.1038/nature02485. ISSN   1476-4687. PMID   15085136. S2CID   4332562.
  9. ↑ Felix, Georg; Duran, Juliana D.; Volko, Sigrid; Boller, Thomas (1999-05-01). "Plants have a sensitive perception system for the most conserved domain of bacterial flagellin". The Plant Journal. 18 (3): 265–276. doi: 10.1046/j.1365-313X.1999.00265.x . ISSN   1365-313X. PMID   10377992.
  10. ↑ Mathieu, Yves; Armen, Kurkdjian; Xia, Hua; Guern, Jean; Koller, Alan; Spiro, Mark D; O'Neill, Malcolm; Albersheim, Peter; Darvill, Alan (1991-11-01). "Membrane responses induced by oligogalacturonides in suspension-cultured tobacco cells". The Plant Journal. 1 (3): 333–343. doi:10.1046/j.1365-313X.1991.t01-10-00999.x. ISSN   1365-313X. PMID   29345772.
  11. ↑ Nürnberger, Thorsten; Nennstiel, Dirk; Jabs, Thorsten; Sacks, Wendy R.; Hahlbrock, Klaus; Scheel, Dierk (1994-08-12). "High affinity binding of a fungal oligopeptide elicitor to parsley plasma membranes triggers multiple defense responses". Cell. 78 (3): 449–460. doi:10.1016/0092-8674(94)90423-5. PMID   8062387. S2CID   9759731.
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