scholarly journals Perturbations of a Kinase-Pseudokinase Module Activate Plant Immunity

2019 ◽  
Author(s):  
D. Patrick Bastedo ◽  
Derek Seto ◽  
Alexandre Martel ◽  
Madiha Khan ◽  
Inga Kireeva ◽  
...  
Keyword(s):  
Immune Response ◽  
Arabidopsis Thaliana ◽  
Immune Responses ◽  
Pseudomonas Syringae ◽  
Molecular Mechanisms ◽  
Kinase Domain ◽  
Host Cells ◽  
In Planta ◽  
Plant Host ◽  
Model Plant

ABSTRACTThe Pseudomonas syringae acetyltransferase HopZ1a is delivered directly into host cells by the type III secretion system to promote bacterial growth. However, in the model plant host Arabidopsis thaliana, HopZ1a activity results in an effector-triggered immune response (ETI) that limits bacterial proliferation. HopZ1a-triggered immunity requires the nucleotide-binding, leucine-rich repeat domain (NLR) protein, ZAR1, and the ZED1 pseudokinase. Here we demonstrate that HopZ1a can acetylate members of a family of ‘receptor-like cytoplasmic kinases’ (RLCK family VII; also known as PBS1-like kinases, or PBLs) and promote their interaction with ZED1 and ZAR1 to form a ZAR1/ZED1/PBL ternary complex. Interactions between ZED1 and PBL kinases are determined by the pseudokinase features of ZED1, and mutants designed to restore ZED1 kinase motifs can (1) bind to PBLs, (2) recruit ZAR1, and (3) trigger immunity in planta, all independently of HopZ1a. Our results suggest that interactions between these two RLCK families are promoted by perturbations of structural features that distinguish active from inactive kinase domain conformations. We propose that effector-induced interactions between ZED1/ZRK pseudokinases (RLCK family XII) and PBL kinases (RLCK family VII) provide a sensitive mechanism for detecting perturbations of either kinase family and activating ZAR1-mediated ETI.AUTHOR SUMMARYAll plants must ward off potentially infectious microbes, and those grown in large-scale crop operations are especially vulnerable to the rapid spread of disease by successful pathogens. Although many bacteria and fungi can supress plant immune responses by producing specialized virulence proteins called ‘effectors’, these effectors can also trigger immune responses that render plants resistant to infection. We studied the molecular mechanisms underlying one such effector-triggered immune response elicited by the bacterial effector HopZ1a in the model plant host Arabidopsis thaliana. We have shown that HopZ1a promotes binding between a ZED1, a ‘pseudokinase’ required for HopZ1a-triggered immunity, and several ‘true kinases’ (known as PBLs) that are likely targets of HopZ1a activity in planta. HopZ1a-induced ZED1-PBL interactions also recruit ZAR1, an Arabidopsis ‘resistance protein’ previously implicated in HopZ1a-triggered immunity. Importantly, ZED1 mutants that restore degenerate kinase motifs can bridge interactions between PBLs and ZAR1 (independently of HopZ1a) and trigger immunity in planta. Our results suggest that equilibria between active and inactive kinase domain conformations regulate ZED1-PBL interactions and formation of ternary complexes with ZAR1. Improved models describing molecular interactions between immunity determinants, effectors and effector targets will inform efforts to exploit natural diversity for development of crops with enhanced disease resistance.

scholarly journals Multiple Xanthomonas euvesicatoria Type III Effectors Inhibit flg22-Triggered Immunity

2016 ◽  
Vol 29 (8) ◽  
pp. 651-660 ◽  
Author(s):  
Georgy Popov ◽  
Malou Fraiture ◽  
Frederic Brunner ◽  
Guido Sessa
Keyword(s):  
Pseudomonas Syringae ◽  
Map Kinases ◽  
Molecular Mechanisms ◽  
Inducible Promoter ◽  
Effector Proteins ◽  
Host Cells ◽  
In Planta ◽  
Callose Deposition ◽  
Type Iii ◽  
Xanthomonas Euvesicatoria

Xanthomonas euvesicatoria is the causal agent of bacterial spot disease in pepper and tomato. X. euvesicatoria bacteria interfere with plant cellular processes by injecting effector proteins into host cells through the type III secretion (T3S) system. About 35 T3S effectors have been identified in X. euvesicatoria 85-10, and a few of them were implicated in suppression of pattern-triggered immunity (PTI). We used an Arabidopsis thaliana pathogen-free protoplast–based assay to identify X. euvesicatoria 85-10 effectors that interfere with PTI signaling induced by the bacterial peptide flg22. Of 33 tested effectors, 17 inhibited activation of a PTI-inducible promoter. Among them, nine effectors also interfered with activation of an abscisic acid–inducible promoter. However, effectors that inhibited flg22-induced signaling did not affect phosphorylation of mitogen-activated protein (MAP) kinases acting downstream of flg22 perception. Further investigation of selected effectors revealed that XopAJ, XopE2, and XopF2 inhibited activation of a PTI-inducible promoter by the bacterial peptide elf18 in Arabidopsis protoplasts and by flg22 in tomato protoplasts. The effectors XopF2, XopE2, XopAP, XopAE, XopH, and XopAJ inhibited flg22-induced callose deposition in planta and enhanced disease symptoms caused by attenuated Pseudomonas syringae bacteria. Finally, selected effectors were found to localize to various plant subcellular compartments. These results indicate that X. euvesicatoria bacteria utilize multiple T3S effectors to suppress flg22-induced signaling acting downstream or in parallel to MAP kinase cascades and suggest they act through different molecular mechanisms.

scholarly journals Extracellular Vesicles from Different Pneumococcal Serotypes Are Internalized by Macrophages and Induce Host Immune Responses

Pathogens ◽  
2021 ◽  
Vol 10 (12) ◽  
pp. 1530
Author(s):  
Alfonso Olaya-Abril ◽  
Rafael Prados-Rosales ◽  
José A. González-Reyes ◽  
Arturo Casadevall ◽  
Liise-anne Pirofski ◽  
...  
Keyword(s):  
Immune Response ◽  
Biological Activity ◽  
Immune Responses ◽  
Extracellular Vesicles ◽  
Host Cells ◽  
Pneumococcal Serotypes ◽  
Human Pathogen ◽  
Host Immune Responses ◽  
Serotype 1 ◽  
Transient Loss

Bacterial extracellular vesicles are membranous ultrastructures released from the cell surface. They play important roles in the interaction between the host and the bacteria. In this work, we show how extracellular vesicles produced by four different serotypes of the important human pathogen, Streptococcus pneumoniae, are internalized by murine J774A.1 macrophages via fusion with the membrane of the host cells. We also evaluated the capacity of pneumococcal extracellular vesicles to elicit an immune response by macrophages. Macrophages treated with the vesicles underwent a serotype-dependent transient loss of viability, which was further reverted. The vesicles induced the production of proinflammatory cytokines, which was higher for serotype 1 and serotype 8-derived vesicles. These results demonstrate the biological activity of extracellular vesicles of clinically important pneumococcal serotypes.

scholarly journals Mycobacterium tuberculosisinhibits human innate immune responses via the production of TLR2 antagonist glycolipids

2017 ◽  
Vol 114 (42) ◽  
pp. 11205-11210 ◽  
Author(s):  
Landry Blanc ◽  
Martine Gilleron ◽  
Jacques Prandi ◽  
Ok-ryul Song ◽  
Mi-Seon Jang ◽  
...  
Keyword(s):  
Immune Responses ◽  
Molecular Mechanisms ◽  
Cytokine Production ◽  
Cell Envelope ◽  
Costimulatory Molecule ◽  
Immune Defense ◽  
Innate Immune ◽  
Host Cells ◽  
Innate Immune Responses ◽  
Reporter System

Mycobacterium tuberculosisis a major human pathogen that is able to survive inside host cells and resist immune clearance. Most particularly, it inhibits several arms of the innate immune response, including phagosome maturation or cytokine production. To better understand the molecular mechanisms by whichM. tuberculosiscircumvents host immune defenses, we used a transposon mutant library generated in a virulent clinical isolate ofM. tuberculosisof the W/Beijing family to infect human macrophages, utilizing a cell line derivative of THP-1 cells expressing a reporter system for activation of the transcription factor NF-κB, a key regulator of innate immunity. We identified severalM. tuberculosismutants inducing a NF-κB activation stronger than that of the wild-type strain. One of these mutants was found to be deficient for the synthesis of cell envelope glycolipids, namely sulfoglycolipids, suggesting that the latter can interfere with innate immune responses. Using natural and synthetic molecular variants, we determined that sulfoglycolipids inhibit NF-κB activation and subsequent cytokine production or costimulatory molecule expression by acting as competitive antagonists of Toll-like receptor 2, thereby inhibiting the recognition ofM. tuberculosisby this receptor. Our study reveals that producing glycolipid antagonists of pattern recognition receptors is a strategy used byM. tuberculosisto undermine innate immune defense. Sulfoglycolipids are major and specific lipids ofM. tuberculosis, considered for decades as virulence factors of the bacilli. Our study uncovers a mechanism by which they may contribute toM. tuberculosisvirulence.

scholarly journals Mechanisms of Action of Probiotics in Intestinal Diseases

2007 ◽  
Vol 7 ◽  
pp. 31-46 ◽  
Author(s):  
Ann M. O'Hara ◽  
Fergus Shanahan
Keyword(s):  
Immune Responses ◽  
Molecular Mechanisms ◽  
Clinical Medicine ◽  
Mechanisms Of Action ◽  
Host Cells ◽  
Positive Health ◽  
Beneficial Effects ◽  
Potential Therapeutic Role ◽  
Conditioning Effect ◽  
Clinical Conditions

Intestinal microbiota is a positive health asset that exerts a conditioning effect on intestinal homeostasis. Resident bacteria deliver regulatory signals to the epithelium and instruct mucosal immune responses. Recent research has revealed a potential therapeutic role for the manipulation of the microbiota and exploitation of host-microbial signalling pathways in the maintenance of human health and treatment of various mucosal disorders. A variety of pharmabiotic strategies, such as the use of specific members of the microbiota, their surface components, or metabolites, as well as genetically modified commensal bacteria, are being investigated for their ability to enhance the beneficial components of the microbiota. It is clear that engagement with host cells is central to pharmabiotic action, and several strain-specific mechanisms of action have been elucidated. However, the molecular details underpinning these mechanisms remain almost entirely unknown. Understanding how pharmabiotics exert their beneficial effects is critical for the establishment of definitive selection criteria for certain pharmabiotic strategies for specific clinical conditions. Scientifically accredited evidence of efficacy and studies to elucidate the molecular mechanisms of host-microbiota interactions are needed to lend credence to the use of pharmabiotic strategies in clinical medicine.

scholarly journals Immunogold Labeling of Hrp Pili of Pseudomonas syringae pv. tomato Assembled in Minimal Medium and In Planta

2001 ◽  
Vol 14 (2) ◽  
pp. 234-241 ◽  
Author(s):  
Wenqi Hu ◽  
Jing Yuan ◽  
Qiao-Ling Jin ◽  
Patrick Hart ◽  
Sheng Yang He
Keyword(s):  
Arabidopsis Thaliana ◽  
Pseudomonas Syringae ◽  
Minimal Medium ◽  
Leaf Tissue ◽  
Hypersensitive Reaction ◽  
Immunogold Labeling ◽  
Structural Protein ◽  
In Planta ◽  
Hrp Genes

Hypersensitive reaction and pathogenicity (hrp) genes are required for Pseudomonas syringae pv. tomato (Pst) DC3000 to cause disease in susceptible tomato and Arabidopsis thaliana plants and to elicit the hypersensitive response in resistant plants. The hrp genes encode a type III protein secretion system known as the Hrp system, which in Pst DC3000 secretes HrpA, HrpZ, HrpW, and AvrPto and assembles a surface appendage, named the Hrp pilus, in hrp-gene-inducing minimal medium. HrpA has been suggested to be the Hrp pilus structural protein on the basis of copurification and mutational analyses. In this study, we show that an antibody against HrpA efficiently labeled Hrp pili, whereas antibodies against HrpW and HrpZ did not. Immunogold labeling of bacteria-infected Arabidopsis thaliana leaf tissue with an Hrp pilus antibody revealed a characteristic lineup of gold particles around bacteria and/or at the bacterium-plant contact site. These results confirm that HrpA is the major structural protein of the Hrp pilus and provide evidence that Hrp pili are assembled in vitro and in planta.

scholarly journals Interaction of bacterial extracellular microvesicles with eukaryotic cells.

2021 ◽  
Vol 22 (6) ◽  
pp. 1065-1084
Author(s):  
D. S. Shlykova ◽  
V. M. Pisarev ◽  
A. M. Gaponov ◽  
A. V. Tutelyan
Keyword(s):  
Immune Response ◽  
Dendritic Cells ◽  
Inflammatory Cytokines ◽  
Human Body ◽  
Molecular Mechanisms ◽  
Host Cells ◽  
Eukaryotic Cells ◽  
Signal Molecules ◽  
Opportunistic Bacteria ◽  
Cytokines Secretion

Bacterial extracellular microvesicles (BMV) are formed by nonpathogenic, pathogenic and opportunistic bacteria. BMV are spherical bilayer-membrane organelles containing different cargoes: lipopolysaccharides, pathogen associated molecular patterns (PUMP), DNA, RNA, signal molecules, proteins, antibiotic resistance factors, virulence factors, toxins providing various immune response options and conducive to the survival and pathogen dissemination in the human body. BMVs secretion play an important role in the ability of microorganisms to cause various diseases. BMV are involved in biofilms formation, help bacteria to obtain nutrition in a nutrient-poor conditions, to evade the host's immune response, provide communication and surviving in a stressful environment during infection inside the host. The heterogeneity of the biogenesis mechanisms causes differences in the BMV and their characteristics including virulence rate. BMVs host cells entering is mediated by several mechanisms and helps to activate innate and adaptive immune reactions. This review focuses on interaction study of BMV with various eukaryotic cells types including neutrophils, dendritic cells, macrophages, epithelial, endothelial cells. This interaction depends on bacteria species, type of target cell and number of vesicles and can lead to different responses: non-immunogenic, pro-inflammatory, cytotoxic. Subcellular and molecular mechanisms related to the involvement of extracellular microvesicles in host's immune response modulation are presented. Stimulation of immune response is provided by increased secretion of proinflammatory cytokines and chemokines. In some cases BMV use mechanisms to evade immune surveillance: anti-inflammatory cytokines secretion, alterations of phagocytosis and chemotaxis of macrophages, increasing the proteolytic cleavage of CD14 on the macrophage surface, alterations of antigen-presenting function of dendritic cells, T-cell proliferation suppression, reducing the pro-inflammatory cytokines secretion, evasion of host-immune cells direct interactions, destruction of neutrophilic traps. These features allow bacterial cells to survive in the human body, increase their invasive potential, and reduce the excessive inflammatory reactions leading to death of the pathogen itself and life-threatening damage of tissues and organs of the host. Further studies of these mechanisms will improve existing therapeutic approaches to the infectious diseases treatment.

scholarly journals molecular link from PAMP perception to a MAPK cascade associated with tomato disease resistance

2012 ◽  
Author(s):  
Guido Sessa ◽  
Gregory B. Martin
Keyword(s):  
Cell Death ◽  
Disease Resistance ◽  
Immune Responses ◽  
Map Kinase ◽  
Pseudomonas Syringae ◽  
Molecular Mechanisms ◽  
Plant Immunity ◽  
Defense Responses ◽  
Research Activities ◽  
Mapk Cascades

The research problem: The detection of pathogen-associated molecular patterns (PAMPs) by plant pattern recognition receptors (PRRs) is a key mechanism by which plants activate an effective immune response against pathogen attack. MAPK cascades are important signaling components downstream of PRRs that transduce the PAMP signal to activate various defense responses. Preliminary experiments suggested that the receptor-like cytoplasmickinase (RLCK) Mai5 plays a positive role in pattern-triggered immunity (PTI) and interacts with the MAPKKK M3Kε. We thus hypothesized that Mai5, as other RLCKs, functions as a component PRR complexes and acts as a molecular link between PAMP perception and activation of MAPK cascades. Original goals: The central goal of this research was to investigate the molecular mechanisms by which Mai5 and M3Kε regulate plant immunity. Specific objectives were to: 1. Determine the spectrum of PAMPs whose perception is transmitted by M3Kε; 2. Identify plant proteins that act downstream of M3Kε to mediate PTI; 3. Investigate how and where Mai5 interacts with M3Kε in the plant cell; 4. Examine the mechanism by which Mai5 contributes to PTI. Changes in research directions: We did not find convincing evidence for the involvement of M3Kε in PTI signaling and substituted objectives 1 and 3 with research activities aimed at the analysis of transcriptomic profiles of tomato plants during the onset of plant immunity, isolation of the novel tomato PRR FLS3, and investigation of the involvement of the RLCKBSKs in PTI. Main achievements during this research program are in the following major areas: 1. Functional characterization of Mai5. The function of Mai5 in PTI signaling was demonstrated by testing the effect of silencing the Mai5 gene by virus-induced gene silencing (VIGS) experiments and in cell death assays. Domains of Mai5 that interact with MAPKKKs and subcellular localization of Mai5 were analyzed in detail. 2. Analysis of transcriptional profiles during the tomato immune responses to Pseudomonas syringae (Pombo et al., 2014). We identified tomato genes whose expression is induced specifically in PTI or in effector-triggered immunity (ETI). Thirty ETI-specific genes were examined by VIGS for their involvement in immunity and the MAPKKK EPK1, was found to be required for ETI. 3. Dissection of MAP kinase cascades downstream of M3Kε (Oh et al., 2013; Teper et al., 2015). We identified genes that encode positive (SGT and EDS1) and negative (WRKY1 and WRKY2) regulators of the ETI-associated cell death mediated by M3Kε. In addition, the MKK2 MAPKK, which acts downstream of M3Kε, was found to interact with the MPK3 MAPK and specific MPK3 amino acids involved interaction were identified and found to be required for induction of cell death. We also identified 5 type III effectors of the bacterial pathogen Xanthomonaseuvesicatoria that inhibited cell death induced by components of ETI-associated MAP kinase cascades. 4. Isolation of the tomato PRR FLS3 (Hind et al., submitted). FLS3, a novel PRR of the LRR-RLK family that specifically recognizes the flagellinepitope flgII-28 was isolated. FLS3 was shown to bind flgII-28, to require kinase activity for function, to act in concert with BAK1, and to enhance disease resistance to Pseudomonas syringae. 5. Functional analysis of RLCKs of the brassinosteroid signaling kinase (BSK) family.Arabidopsis and tomato BSKs were found to interact with PRRs. In addition, certain ArabidospsisBSK mutants were found to be impaired in PAMP-induced resistance to Pseudomonas syringae. Scientific and agricultural significance: Our research activities discovered and characterized new molecular components of signaling pathways mediating recognition of invading pathogens and activation of immune responses against them. Increased understanding of molecular mechanisms of immunity will allow them to be manipulated by both molecular breeding and genetic engineering to produce plants with enhanced natural defense against disease.

scholarly journals Exploration of Pattern Recognition Receptor Agonists as Candidate Adjuvants

2021 ◽  
Vol 11 ◽  
Author(s):  
Guang Han Ong ◽  
Benedict Shi Xiang Lian ◽  
Takumi Kawasaki ◽  
Taro Kawai
Keyword(s):  
Immune Responses ◽  
Molecular Mechanisms ◽  
Innate Immune ◽  
Host Cells ◽  
Vaccine Adjuvants ◽  
Immune Reactions ◽  
Safety And Reliability ◽  
Pathogen Recognition Receptors ◽  
Acquired Immune Responses ◽  
Molecular Patterns

Adjuvants are used to maximize the potency of vaccines by enhancing immune reactions. Components of adjuvants include pathogen-associated molecular patterns (PAMPs) and damage-associate molecular patterns (DAMPs) that are agonists for innate immune receptors. Innate immune responses are usually activated when pathogen recognition receptors (PRRs) recognize PAMPs derived from invading pathogens or DAMPs released by host cells upon tissue damage. Activation of innate immunity by PRR agonists in adjuvants activates acquired immune responses, which is crucial to enhance immune reactions against the targeted pathogen. For example, agonists for Toll-like receptors have yielded promising results as adjuvants, which target PRR as adjuvant candidates. However, a comprehensive understanding of the type of immunological reaction against agonists for PRRs is essential to ensure the safety and reliability of vaccine adjuvants. This review provides an overview of the current progress in development of PRR agonists as vaccine adjuvants, the molecular mechanisms that underlie activation of immune responses, and the enhancement of vaccine efficacy by these potential adjuvant candidates.

scholarly journals ATF6β is a host cellular target of the Toxoplasma gondii virulence factor ROP18

2011 ◽  
Vol 208 (7) ◽  
pp. 1533-1546 ◽  
Author(s):  
Masahiro Yamamoto ◽  
Ji Su Ma ◽  
Christina Mueller ◽  
Naganori Kamiyama ◽  
Hiroyuki Saiga ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Immune Responses ◽  
Virulence Factor ◽  
Molecular Mechanisms ◽  
Host Cells ◽  
Type I ◽  
Cellular Functions ◽  
Susceptibility To Infection ◽  
Pathogenic Action ◽  
Acute Toxoplasmosis

The ROP18 kinase has been identified as a key virulence determinant conferring a high mortality phenotype characteristic of type I Toxoplasma gondii strains. This major effector molecule is secreted by the rhoptries into the host cells during invasion; however, the molecular mechanisms by which this kinase exerts its pathogenic action remain poorly understood. In this study, we show that ROP18 targets the host endoplasmic reticulum–bound transcription factor ATF6β. Disruption of the ROP18 gene severely impairs acute toxoplasmosis by the type I RH strain. Because another virulence factor ROP16 kinase modulates immune responses through its N-terminal portion, we focus on the role of the N terminus of ROP18 in the subversion of host cellular functions. The N-terminal extension of ROP18 contributes to ATF6β-dependent pathogenicity by interacting with ATF6β and destabilizing it. The kinase activity of ROP18 is essential for proteasome-dependent degradation of ATF6β and for parasite virulence. Consistent with a key role for ATF6β in resistance against this intracellular pathogen, ATF6β-deficient mice exhibit a high susceptibility to infection by ROP18-deficient parasites. The results reveal that interference with ATF6β-dependent immune responses is a novel pathogenic mechanism induced by ROP18.

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