Calcium signaling in plant defense (involvement of subcellular compartments and glutamate receptors)

Les plantes présentent une forme d immunité innée face à des agents potentiellement pathogènes qui se traduit par l induction de réponses de défense. Les réponses immunes des plantes sont induites après détection de motifs moléculaires associés à des pathogènes ou à des micro-organismes par des récepteurs reconnaissant spécifiquement ces motifs et/ou des molécules dérivées des agents pathogènes ou de la plante, appelés éliciteurs de réaction de défense. La cryptogéine (Cry) et les oligogalacturonates (OGs) sont des éliciteurs établis de réactions de défense et leur reconnaissance induit une signalisation Ca2+-dépendante : un influx calcique et une variation de la concentration cytosolique en Ca2+ libre ([Ca]cyt) sont des événements précoces induisant une voie de signalisation de défense. Nous avons démontré que chez le tabac, les éliciteurs induisent une signalisation calcique dans les mitochondries et les chloroplastes. Des études pharmacologiques indiquent que des canaux IP3-dépendants régulent la signalisation calcique induite par la Cry dans les mitochondries et les chloroplastes. La respiration mitochondriale et les mécanismes de dissipation de l énergie dans les chloroplastes sont régulés en partie par la [Ca2+] dans ces organites. De plus, nous montrons par des approches pharmacologiques et génétiques, que des homologues aux récepteurs du glutamate (GLRs) participent à la signalisation calcique induite par les OGs dans Arabidopsis. Les GLRs contrôlent en partie la production d oxyde nitrique (NO) et d espèces réactives de l oxygène (ROS), ainsi que l expression de gènes de défense. Par ailleurs, les plantes traitées par des antagonistes des GLRs, présentent une moindre résistance au pathogène fongique nécrotrophique, Botrytis cinerea et à l oomycète biotrophique, Hyaloperonospora arabidopsidis. L analyse de mutants Atglr révèle l importante contribution de AtGLR3.3 dans la résistance envers H. arabidopsidis. De plus, de frappantes similarités dans l expression de gènes sont observées après traitement par les OGs ou après infection par H. arabidopsidis. Enfin, une analyse transcriptomique montre qu environ 60 % des gènes modulés par les OGs ont une expression qui dépend de GLRs. Ces gènes dépendants de GLRs appartiennent à diverses familles fonctionnelles dont celle répondant aux stress biotiques. En conclusion, ces études montrent 1) que les mitochondries et les chloroplastes présentent aussi une signalisation calcique induite par des éliciteurs de réaction de défense chez le tabac et 2) l implication de GLRs dans la signalisation calcique induite par des éliciteurs ou des agents pathogènes et la résistance envers des agents pathogènes chez ArabidopsisPlants do not display an adaptive immune system but express an efficient innate immune system defending them by inducing sophisticated multilevel defense responses against different potential pathogens. Indeed, plant immune responses are triggered upon the detection of many common pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) through specific pattern-recognition receptors (PRRs) and/or pathogen- or plant-derived signal molecules called elicitors. Cryptogein (Cry) and oligogalacturonides (OGs) are well known elicitors of defense reactions and their recognition induce a Ca2+-dependent signaling pathway: Ca2+ influx and subsequent free cytosolic [Ca2+] ([Ca2+]cyt) variations are earliest steps to trigger downstream plant defense signaling. Here we have demonstrated that elicitor-induced Ca2+ signaling in tobacco also takes place in mitochondria and chloroplasts. Pharmacological studies indicated that IP3-channels play an important role in the regulation of Ca2+ signaling in mitochondria and chloroplasts. Mitochondrial respiration and energy dissipation mechanisms in chloroplasts are partly controlled by [Ca2+] in these organelles. Moreover, using pharmacological and genetic approaches, our data demonstrated that glutamate receptors homologs (GLRs) participate in OGs-mediated Ca2+ signaling in Arabidopsis. GLRs partly control OGs-induced nitric oxide (NO) production, reactive oxygen species (ROS) production and expression of defense-related genes. Importantly, plants treated with GLRs antagonists exhibited compromised resistance to necrotrophic fungal pathogen, Botrytis cinerea and biotrophic oomycete, Hyaloperonospora arabidopsidis. Analysis of Atglr single mutants revealed the important contribution of AtGLR3.3 in resistance against H. arabidopsidis. Moreover, striking similarities in gene expression levels were observed after OGs elicitation/H. arabidopsidis infection. Finally, transcriptomic analysis demonstrated that about 60 % of the total OGs-modulated genes modified their expression in GLRs-dependent manner. These GLRs-dependent genes belong to different functional categories including the category responses to biotic stresses . Taken together, these data provide strong evidences of 1) elicitor-induced Ca2+ signaling in mitochondria and chloroplasts in tobacco and 2) the regulation of elicitor/pathogen mediated plant defense signaling pathways through GLRs in Arabidopsis thalianaDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Etude de la signalisation calcique induite par le glutamate chez le tabac (un récepteur du glutamate putatif comme nouvel acteur dans la défense des plantes)

Chez les mammifères, le glutamate est un neuromédiateur bien connu au niveau du système nerveux central et plus récemment un rôle immunomodulateur lui a été reconnu. Le glutamate est le ligand de récepteurs ionotopiques (iGluRs) qui sont des récepteurs-canaux perméables à divers cations dont le calcium (non-selective cation channels, NSCC). Chez Arabidopsis thaliana, une famille de 20 gènes de iGluRs homologues des iGluRs de mammifères a été identifiée et leur implication dans divers processus biologiques est suggérée. Dans ce travail où nous utilisons des suspensions de cellules de tabac (Nicotiana tabacum var Xanthi), divers arguments suggèrent que ces iGluR sont fonctionnels dans le tabac : influx de calcium et élévation rapide et transitoire de la concentration en calcium cytosolic libre en réponse à l addition de glutamate, inhibition de ces effets par 4 antagonistes de iGluRs animaux (compétitifs ou non compétitifs), désensibilisation, et pH dépendance des effets. Pour la première fois chez les plantes nous montrons que le glutamate induit la production de NO très vraisemblablement via l activation de iGluRs. De plus, nous démontrons que ce(s) iGluRs sont impliqués dans le mode d action, via les flux de calcium, de la cryptogéine une protéine de 10 kDa de Phytophthora cryptogea, éliciteur des réactions de défense chez le tabac. Néanmoins, à ce niveau, les iGluRs ne sont pas impliqués dans la plupart des événements calcium-dépendants induits par la cryptogéine dont l activation des MAPKs et de canaux anioniques, la production de H2O2 (activation de la NADPH-oxydase) et la réponse hypersensible. En revanche, ils sont tout ou partiellement responsables de la production de NO décrite pour la première fois par le passé en réponse à la cryptogéine. Ces résultats suggèrent que différents types de canaux calciques activés par divers médiateurs, génèrent, via le calcium, des messages spécifiques décodés par des protéines associées à chacun de ces types de canaux et impliquées dans des réponses biologiques différentes. Dans le mode d action de la cryptogéine, nous démontrons que l activation des iGluRs est possible grâce à l exocytose de glutamate dans l apoplaste, induite par la cryptogéine. Ainsi, ce travail est la première démonstration du rôle de iGluRs potentiels dans la défense chez les plantes et de leur implication dans la production de NO. Nos résultats sont un argument supplémentaire à la conservation des mécanismes de la défense dans le monde vivant et posent le problème du rôle du glutamate dans la signalisation chez les plantes.Glutamate is recognized as the primary excitatory neurotransmitter in the mammalian central nervous system (CNS) but recent studies have shown that glutamate has an important additional immunomodulator role. Glutamate is the ligand of ionotropic glutamate receptors (iGluRs), which are non-selective cation channels (NSCC), permeable to calcium. In plants, animal iGluR homologs were found that were involved in many developmental processes. Here we demonstrate the involvement of putative iGluRs in calcium signalling in response to cryptogein which is a 10 kDa protein secreted by the oomycete Phytophthora cryptogea and is an elicitor of defence in tobacco. Using transformed tobacco cell suspensions expressing aequorin in the cytosol or in the nucleus, our results have shown that glutamate induces a strong and transient [Ca2+]cyt elevation without [Ca2+]nuc changes. Glutamate-induced [Ca2+]cyt elevation was a result of calcium influx from the extracellular medium and was inhibited by different GluR inhibitors. This data suggest the presence of functional calcium channels of GluRs-type in tobacco. Nevertheless, glutamate does not induce some of the calcium-dependent characteristic events of the defence pathways, which are H2O2 production, MAPK activation and hypersensitive response, but promoted NO production. Further, Ca2+ influx,[Ca2+]cyt elevation and NO production induced by cryptogein were shown to be partially inhibited by the glutamate receptor inhibitors, suggesting that cryptogein treatment could activate a calcium channel of the GluR-type leading to plant defense signalling through NO production. We have also demonstrated that cryptogein induces an efflux of glutamate in the apoplast by the process of exocytosis thus activating the GluRs in tobacco. This is the first demonstration for a potential GluR(s) involvement in plant defense signalling, furthermore by mechanisms that showed homology with glutamate effect on neuronal cells.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Involvement of putative glutamate receptors in plant defence signaling and NO production

International audienceIonotropic glutamate receptors (iGluRs) are non-selective cation channels permeable to calcium, present in animals and plants. In mammals, glutamate is a well-known neurotransmitter and recently has been recognized as an immunomodulator. As animals and plants share common mechanisms that govern innate immunity with calcium playing a key role in plant defence activation, we have checked the involvement of putative iGluRs in plant defence signaling. Using tobacco cells, we first provide evidence supporting the activity of iGluRs as calcium channels and their involvement in NO production as reported in animals. Thereafter, iGluRs were shown to be activated in response to cryptogein, a well studied elicitor of defence response, and partly responsible for cryptogein-induced NO production. However, other cryptogein-induced calcium-dependent events including anion efflux, H2O2 production, MAPK activation and hypersensitive response (HR) did not depend on iGluRs indicating that different calcium channels regulate different processes at the cell level. We have also demonstrated that cryptogein induces efflux of glutamate in the apoplast by exocytosis. Taken together, our results demonstrate for the first time, an involvement of a putative iGluR in plant defence signaling and NO production, by mechanisms that show homology with glutamate mode of action in mammals

Calcium signatures and signaling in cytosol and organelles of tobacco cells induced by plant defense elicitors

International audienceCalcium signatures induced by two elicitors of plant defense reactions, namely cryptogein and oligogalacturonides, were monitored at the subcellular level, using apoaequorin-transformed Nicotiana tabacum var Xanthi cells, in which the apoaequorin calcium sensor was targeted either to cytosol, mitochondria or chloroplasts. Our study showed that both elicitors induced specific Ca2+ signatures in each compartment, with the most striking difference relying on duration. Common properties also emerged from the analysis of Ca2+ signatures: both elicitors induced a biphasic cytosolic [Ca2+] elevation together with a single mitochondrial [Ca2+] elevation concomitant with the first cytosolic [Ca2+] peak. In addition, both elicitors induced a chloroplastic [Ca2+] elevation peaking later in comparison to cytosolic [Ca2+] elevation. In cryptogein-treated cells, pharmacological studies indicated that IP3 should play an important role in Ca2+ signaling contrarily to cADPR or nitric oxide, which have limited or no effect on [Ca2+] variations. Our data also showed that, depending on [Ca2+] fluxes at the plasma membrane, cryptogein triggered a mitochondrial respiration increase and affected excess energy dissipation mechanisms in chloroplasts. Altogether the results indicate that cryptogein profoundly impacted cell functions at many levels, including organelles. (C) 2012 Elsevier Ltd. All rights reserved

Involvement of the glutamate receptor AtGLR3.3 in plant defense signaling and resistance to Hyaloperonospora arabidopsidis

International audienceLike their animal counterparts, plant glutamate receptor-like (GLR) homologs are intimately associated with Ca2+ influx through plasma membrane and participate in various physiological processes. In pathogen-associated molecular patterns (PAMP)-/elicitor-mediated resistance, Ca2+ fluxes are necessary for activating downstream signaling events related to plant defense. In this study, oligogalacturonides (OGs), which are endogenous elicitors derived from cell wall degradation, were used to investigate the role of Arabidopsis GLRs in defense signaling. Pharmacological investigations indicated that GLRs are partly involved in free cytosolic [Ca2+] ([Ca2+](cyt)) variations, nitric oxide (NO) production, reactive oxygen species (ROS) production and expression of defense-related genes by OGs. In addition, wild-type Col-0 plants treated with the glutamate-receptor antagonist 6,7-dinitriquinoxaline-2,3-dione (DNQX) had a compromised resistance to Botrytis cinerea and Hyaloperonospora arabidopsidis. Moreover, we provide genetic evidence that AtGLR3.3 is a key component of resistance against H.arabidopsidis. In addition, some OGs-triggered immune events such as defense gene expression, NO and ROS production are also to different extents dependent on AtGLR3.3. Taken together, these data provide evidence for the involvement of GLRs in elicitor/pathogen-mediated plant defense signaling pathways in Arabidopsis thaliana

Early signaling events induced by elicitors of plant defenses

International audiencePlant pathogen attacks are perceived through pathogenissued compounds or plant-derived molecules that elicit defense reactions. Despite the large variety of elicitors, general schemes for cellular elicitor signaling leading to plant resistance can be drawn. In this article, we review early signaling events that happen after elicitor perception, including reversible protein phosphorylations, changes in the activities of plasma membrane proteins, variations in free calcium concentrations in cytosol and nucleus, and production of nitric oxide and active oxygen species. These events occur within the first minutes to a few hours after elicitor perception. One specific elicitor transduction pathway can use a combination or a partial combination of such events which can differ in kinetics and intensity depending on the stimulus. The links between the signaling events allow amplification of the signal transduction and ensure specificity to get appropriate plant defense reactions. This review first describes the early events induced by cryptogein, an elicitor of tobacco defense reactions, in order to give a general scheme for signal transduction that will be use as a thread to review signaling events monitored in different elicitor or plant models

Caractérisation du mode d’action des rhamnolipides dans la défense des plantes et l’induction d’une résistance contre des agents phytopathogènes biotrophes et nécrotrophes

National audienceLes rhamnolipides (RL) sont des glycolipides amphiphiles produits par différentes bactéries notamment du genre Pseudomonas et Burkholderia. Les RL comprennent généralement une chaîne d’acides gras couplée à un ou plusieurs rhamnoses. Il sont impliqués dans la formation de biofilms, dans la mobilité bactérienne et constituent, pour certaines bactéries, des facteurs de virulence (Vatsa et al. 2010). Nous avons montré que les RL sont perçus en tant qu’éliciteurs par les cellules de vigne et que cette reconnaissance provoque un influx de Ca2+, l’activation de plusieurs MAPK (Mitogen-Activated Protein Kinase), la production de formes actives de l’oxygène ainsi que l’expression d’une batterie de gènes de défense. Les RL permettent de protéger efficacement des vitroplants de vigne contre le champignon nécrotrophe Botrytis cinerea (Varnier et al. 2009). Les RL sont aussi capables de potentialiser les réponses de défense activées par d’autres éliciteurs, notamment issus de B. cinerea. Chez la plante modèle Arabidopsis thaliana, le prétraitement avec les RL active une résistance à l’oomycète biotrophe Hyaloperonospora arabidopsidis, à la bactérie hémibiotrophe Pseudomonas syringae pv. tomato ainsi qu’au champignon B. cinerea. En utilisant une approche mutant, nous avons démontré que la résistance induite par les RL implique des voies de signalisation différentes en fonction du type d’interaction (Sanchez et al. 2012). D’autre part, les RL ont une activité antimicrobienne directe sur les champignons ou les oomycètes. De manière plus générale, les RL sont reconnus pour leurs propriétés de biosurfactants et leur potentiel en bioremédiation. Ils sont aussi utilisés dans l’industrie alimentaire. Nos résultats suggèrent que ces molécules ont un potentiel important pour une utilisation en tant que SDN (stimulateur de défense naturel) dans le cadre de stratégies alternatives de lutte parasitaire chez la vigne. Sanchez L, Courteaux B, Hubert J, Kauffmann S, Renault JH, et al. (2012) Rhamnolipids Elicit Defense Responses and Induce Disease Resistance against Biotrophic, Hemibiotrophic, and Necrotrophic Pathogens That Require Different Signaling Pathways in Arabidopsis and Highlight a Central Role for Salicylic Acid. Plant Physiology 160: 1630-1641. Vatsa P, Sanchez L, Clément C, Baillieul F, Dorey S (2010) Rhamnolipid biosurfactants as new players in animal and plant defense against microbes. International Journal of Molecular Sciences 11: 5095-5108. Varnier AL, Sanchez L, Vatsa P, Boudesocque L, Garcia-Brugger A, et al. (2009) Bacterial rhamnolipids are novel MAMPs conferring resistance to Botrytis cinerea in grapevine. Plant, Cell & Environment 32: 178-193

Bacterial rhamnolipids are novel MAMPs conferring resistance to Botrytis cinerea in grapevine

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Impact of sex and gender on post-COVID-19 syndrome, Switzerland, 2020.

Background Women are overrepresented among individuals with post-acute sequelae of SARS-CoV-2 infection (PASC). Biological (sex) as well as sociocultural (gender) differences between women and men might account for this imbalance, yet their impact on PASC is unknown. Aim We assessed the impact of sex and gender on PASC in a Swiss population. Method Our multicentre prospective cohort study included 2,856 (46% women, mean age 44.2 ± 16.8 years) outpatients and hospitalised patients with PCR-confirmed SARS-CoV-2 infection.ResultsAmong those who remained outpatients during their first infection, women reported persisting symptoms more often than men (40.5% vs 25.5% of men; p < 0.001). This sex difference was absent in hospitalised patients. In a crude analysis, both female biological sex (RR = 1.59; 95% CI: 1.41-1.79; p < 0.001) and a score summarising gendered sociocultural variables (RR = 1.05; 95% CI: 1.03-1.07; p < 0.001) were significantly associated with PASC. Following multivariable adjustment, biological female sex (RR = 0.96; 95% CI: 0.74-1.25; p = 0.763) was outperformed by feminine gender-related factors such as a higher stress level (RR = 1.04; 95% CI: 1.01-1.06; p = 0.003), lower education (RR = 1.16; 95% CI: 1.03-1.30; p = 0.011), being female and living alone (RR = 1.91; 95% CI: 1.29-2.83; p = 0.001) or being male and earning the highest income in the household (RR = 0.76; 95% CI: 0.60-0.97; p = 0.030). Conclusion Specific sociocultural parameters that differ in prevalence between women and men, or imply a unique risk for women, are predictors of PASC and may explain, at least in part, the higher incidence of PASC in women. Once patients are hospitalised during acute infection, sex differences in PASC are no longer evident

Machine learning using the extreme gradient boosting (XGBoost) algorithm predicts 5-day delta of SOFA score at ICU admission in COVID-19 patients

Background: Accurate risk stratification of critically ill patients with coronavirus disease 2019 (COVID-19) is essential for optimizing resource allocation, delivering targeted interventions, and maximizing patient survival probability. Machine learning (ML) techniques are attracting increased interest for the development of prediction models as they excel in the analysis of complex signals in data-rich environments such as critical care. Methods: We retrieved data on patients with COVID-19 admitted to an intensive care unit (ICU) between March and October 2020 from the RIsk Stratification in COVID-19 patients in the Intensive Care Unit (RISC-19-ICU) registry. We applied the Extreme Gradient Boosting (XGBoost) algorithm to the data to predict as a binary out- come the increase or decrease in patients’ Sequential Organ Failure Assessment (SOFA) score on day 5 after ICU admission. The model was iteratively cross-validated in different subsets of the study cohort. Results: The final study population consisted of 675 patients. The XGBoost model correctly predicted a decrease in SOFA score in 320/385 (83%) critically ill COVID-19 patients, and an increase in the score in 210/290 (72%) patients. The area under the mean receiver operating characteristic curve for XGBoost was significantly higher than that for the logistic regression model (0.86 vs . 0.69, P < 0.01 [paired t -test with 95% confidence interval]). Conclusions: The XGBoost model predicted the change in SOFA score in critically ill COVID-19 patients admitted to the ICU and can guide clinical decision support systems (CDSSs) aimed at optimizing available resources