Transition to Chaos in an acoustically-driven cavity flow

We consider the unsteady regimes of an acoustically-driven jet that forces a recirculating flow through successive reflections on the walls of a square cavity. The specific question being addressed is to know whether the system can sustain states of low-dimensional chaos when the acoustic intensity driving the jet is increased, and, if so, to characterise the pathway and underlying physical mechanisms. We adopt two complementary approaches, both based on data extracted from numerical simulations: (i) We first characterise successive bifurcations through the analysis of leading frequencies. Two successive phases in the evolution of the system are singled out in this way, both leading to potentially chaotic states. The two phases are separated by a drastic simplification of the dynamics that immediately follows the emergence of intermittency. The second phase also features a second intermediate state where the dynamics is simplified due to frequency-locking. (ii) Nonlinear time series analysis enables us to reconstruct the attractor of the underlying dynamical system, and to calculate its correlation dimension and leading Lyapunov exponent. Both these quantities bring confirmation that the state preceding the dynamic simplification that initiates the second phase is chaotic. Poincar\'e maps further reveal that this chaotic state in fact results from a dynamic instability of the system between two non-chaotic states respectively observed at slightly lower and slightly higher acoustic forcing.Comment: 28 pages, 19 figure

Phytosphingosine-phosphate is a signal for AtMPK6 activation and Arabidopsis response to chilling

Long-chain bases (LCBs) are pleiotropic sphingolipidic signals in eukaryotes. We investigated the source and function of phytosphingosine-1-phosphate (PHS-P), a phospho-LCB rapidly and transiently formed in Arabidopsis thaliana on chilling.PHS-P was analysed by thin-layer chromatography following in vivo metabolic radiolabelling. Pharmacological and genetic approaches were used to identify the sphingosine kinase isoforms involved in cold-responsive PHS-P synthesis. Gene expression, mitogen-activated protein kinase activation and growth phenotypes of three LCB kinase mutants (lcbk1, sphk1 and lcbk2) were studied following cold exposure. Chilling provoked the rapid and transient formation of PHS-P in Arabidopsis cultured cells and plantlets. Cold-evoked PHS-P synthesis was reduced by LCB kinase inhibitors and abolished in the LCB kinase lcbk2 mutant, but not in lcbk1 and sphk1 mutants. lcbk2 presented a constitutive AtMPK6 activation at 22°C. AtMPK6 activation was also triggered by PHS-P treatment independently of PHS/PHS-P balance. lcbk2 mutants grew comparably with wild-type plants at 22 and 4°C, but exhibited a higher root growth at 12°C, correlated with an altered expression of the cold-responsive DELLA gene RGL3. Together, our data indicate a function for LCBK2 in planta. Furthermore, they connect PHS-P formation with plant response to cold, expanding the field of LCB signalling in plants

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

Looking for suppressors of the induced toxicity by the type 3 effector DspA/E in Arabidopsis thaliana and study of the oxidative stress during the infection.

La bactérie Erwinia amylovora est responsable de la maladie du feu bactérien des Maleae (pommier, poirier…). Le pouvoir pathogène de cette bactérie dépend d'une seringue moléculaire appelé système de sécrétion de type 3 (SSTT). Ce SSTT permet à la bactérie d’injecter des effecteurs dans les cellules de la plante. Parmi les effecteurs injectés, DspA/E est l'effecteur indispensable au pouvoir pathogène d’E. amylovora. Cet effecteur est à lui seul capable de provoquer la mort des cellules chez le pommier et le tabac et permet à la bactérie de se multiplier de manière transitoire chez A. thaliana. L’objectif de ce travail de thèse était de comprendre la fonction de DspA/E dans la cellule végétale et d’identifier des facteurs végétaux impliqués dans la toxicité de DspA/E. Afin de répondre à cette question, des plantes transgéniques exprimant DspA/E sous contrôle d’un promoteur inductible à l’estradiol ont été construites.Dans un premier temps, la caractérisation phénotypique des lignées exprimant DspA/E a été effectuée. Les résultats obtenus montrent que DspA/E est toxique lorsqu'il est exprimé in planta (il provoque la mort des cellules, inhibe la germination, la croissance racinaire et la traduction) et permet la multiplication in planta d’un mutant dspA/E. Un crible de mutants suppresseurs de la toxicité de l'effecteur DspA/E a été effectué sur une lignée transgénique exprimant DspA/E dans le but d'identifier un ou plusieurs gènes impliqués dans la toxicité de DspA/E. Ce crible suppresseur a permis d'identifier un candidat potentiel impliqué dans la photo-respiration, la glycolate oxydase 2 (GOX2). L’analyse fonctionnelle réalisée sur le mutant gox2-2 a permis de montrer que le gène GOX2 est un régulateur positif des réponses de défense d’A. thaliana en réponse à l’infection par E. amylovora.Enfin, la caractérisation du stress oxydant a permis de montrer que plusieurs formes actives de l’oxygène (H2O2 et O2.-) s’accumulent au cours de l’interaction entre A. thaliana et E. amylovora. Ceci a permis également de comprendre le rôle de DspA/E sur ce stress oxydant. Nos résultats suggèrent que la glycolate oxydase 2 participerait à l’induction du stress oxydant en perturbant le métabolisme des sucres.The bacterium E. amylovora is responsible for the fire blight disease of Maleae (apple, pear…). The pathogenicity of this bacterium relies on a molecular syringe, the type three secretion system (TTSS). This TTSS allows the bacterium to inject effector proteins into the plant cell. Among these effectors, DspA/E is essential for the pathogenicity of E. amylovora. This effector can provoke cell death on apple and tobacco and allows the bacterium to multiply transiently in A. thaliana.The purpose of the thesis was to understand the function of DspA/E in the plant cell and to identify plant factors involved in the toxicity of DspA/E. To answer this question, transgenic plants which express DspA/E under an estradiol-inducible promoter were built.At first, phenotypical characterization of DspA/E transgenic lines was performed. Our results showed that DspA/E is toxic when expressed in planta (it provokes cell death, inhibits germination, root growth and translation) and allows in planta multiplication of dspA/E bacterial mutant. A screening for suppressor mutants of DspA/E toxicity was performed on a DspA/E transgenic line in order to identify one or several genes involved in the toxicity of DspA/E. This screening allowed us to identify a potential candidate involved in photorespiration, the glycolate oxidase 2 (GOX2). Functional analysis performed on the gox2-2 mutant allowed us to show that the GOX2 gene is a positive regulator of A. thaliana responses against E. amylovora.Finally, characterization of oxidative stress allowed us to show that several reactive oxygen species (H2O2 et O2.-) accumulate during A. thaliana and E. amylovora interaction. This allowed us to understand the role of DspA/E in the oxidative stress. Our results suggest that the glycolate oxidase 2 could be involved in the induction of the oxidative stress by disrupting sugar metabolism

Recherche de suppresseurs de la toxicité induite chez Arabidopsis thaliana par l’effecteur de type 3 DspA/E et étude du stress oxydant au cours de l’infection

The bacterium E. amylovora is responsible for the fire blight disease of Maleae (apple, pear…). The pathogenicity of this bacterium relies on a molecular syringe, the type three secretion system (TTSS). This TTSS allows the bacterium to inject effector proteins into the plant cell. Among these effectors, DspA/E is essential for the pathogenicity of E. amylovora. This effector can provoke cell death on apple and tobacco and allows the bacterium to multiply transiently in A. thaliana.The purpose of the thesis was to understand the function of DspA/E in the plant cell and to identify plant factors involved in the toxicity of DspA/E. To answer this question, transgenic plants which express DspA/E under an estradiol-inducible promoter were built.At first, phenotypical characterization of DspA/E transgenic lines was performed. Our results showed that DspA/E is toxic when expressed in planta (it provokes cell death, inhibits germination, root growth and translation) and allows in planta multiplication of dspA/E bacterial mutant. A screening for suppressor mutants of DspA/E toxicity was performed on a DspA/E transgenic line in order to identify one or several genes involved in the toxicity of DspA/E. This screening allowed us to identify a potential candidate involved in photorespiration, the glycolate oxidase 2 (GOX2). Functional analysis performed on the gox2-2 mutant allowed us to show that the GOX2 gene is a positive regulator of A. thaliana responses against E. amylovora.Finally, characterization of oxidative stress allowed us to show that several reactive oxygen species (H2O2 et O2.-) accumulate during A. thaliana and E. amylovora interaction. This allowed us to understand the role of DspA/E in the oxidative stress. Our results suggest that the glycolate oxidase 2 could be involved in the induction of the oxidative stress by disrupting sugar metabolism.La bactérie Erwinia amylovora est responsable de la maladie du feu bactérien des Maleae (pommier, poirier…). Le pouvoir pathogène de cette bactérie dépend d'une seringue moléculaire appelé système de sécrétion de type 3 (SSTT). Ce SSTT permet à la bactérie d’injecter des effecteurs dans les cellules de la plante. Parmi les effecteurs injectés, DspA/E est l'effecteur indispensable au pouvoir pathogène d’E. amylovora. Cet effecteur est à lui seul capable de provoquer la mort des cellules chez le pommier et le tabac et permet à la bactérie de se multiplier de manière transitoire chez A. thaliana. L’objectif de ce travail de thèse était de comprendre la fonction de DspA/E dans la cellule végétale et d’identifier des facteurs végétaux impliqués dans la toxicité de DspA/E. Afin de répondre à cette question, des plantes transgéniques exprimant DspA/E sous contrôle d’un promoteur inductible à l’estradiol ont été construites.Dans un premier temps, la caractérisation phénotypique des lignées exprimant DspA/E a été effectuée. Les résultats obtenus montrent que DspA/E est toxique lorsqu'il est exprimé in planta (il provoque la mort des cellules, inhibe la germination, la croissance racinaire et la traduction) et permet la multiplication in planta d’un mutant dspA/E. Un crible de mutants suppresseurs de la toxicité de l'effecteur DspA/E a été effectué sur une lignée transgénique exprimant DspA/E dans le but d'identifier un ou plusieurs gènes impliqués dans la toxicité de DspA/E. Ce crible suppresseur a permis d'identifier un candidat potentiel impliqué dans la photo-respiration, la glycolate oxydase 2 (GOX2). L’analyse fonctionnelle réalisée sur le mutant gox2-2 a permis de montrer que le gène GOX2 est un régulateur positif des réponses de défense d’A. thaliana en réponse à l’infection par E. amylovora.Enfin, la caractérisation du stress oxydant a permis de montrer que plusieurs formes actives de l’oxygène (H2O2 et O2.-) s’accumulent au cours de l’interaction entre A. thaliana et E. amylovora. Ceci a permis également de comprendre le rôle de DspA/E sur ce stress oxydant. Nos résultats suggèrent que la glycolate oxydase 2 participerait à l’induction du stress oxydant en perturbant le métabolisme des sucres

The bile acid deoxycholate elicits defences in Arabidopsis and reduces bacterial infection

Disease has an effect on crop yields, causing significant losses. As the worldwide demand for agricultural products increases, there is a need to pursue the development of new methods to protect crops from disease. One mechanism of plant protection is through the activation of the plant immune system. By exogenous application, 'plant activator molecules' with elicitor properties can be used to activate the plant immune system. These defence-inducing molecules represent a powerful and often environmentally friendly tool to fight pathogens. We show that the secondary bile acid deoxycholic acid (DCA) induces defence in Arabidopsis and reduces the proliferation of two bacterial phytopathogens: Erwinia amylovora and Pseudomonas syringae pv. tomato. We describe the global defence response triggered by this new plant activator in Arabidopsis at the transcriptional level. Several induced genes were selected for further analysis by quantitative reverse transcription-polymerase chain reaction. We describe the kinetics of their induction and show that abiotic stress, such as moderate drought or nitrogen limitation, does not impede DCA induction of defence. Finally, we investigate the role in the activation of defence by this bile acid of the salicylic acid biosynthesis gene SID2, of the receptor-like kinase family genes WAK1-3 and of the NADPH oxidase-encoding RbohD gene. Altogether, we show that DCA constitutes a promising molecule for plant protection which can induce complementary lines of defence, such as callose deposition, reactive oxygen species accumulation and the jasmonic acid and salicylic acid signalling pathways

Normal PAI-2 level in French FXII-HAE patients.

International audienc

Every cloud has a silver lining: how abiotic stresses affect gene expression in plant pathogen-interactions.

The current context of environmental and climate changes deeply influences the outcome of plant-pathogen interactions. Indeed, nowadays it is clear that abiotic stresses strongly affect biotic interactions at various levels. For instance, physiological parameters such as plant architecture and tissue organization along with primary and specialized metabolism are affected by environmental constraints, thus making the plant a more or less worthy host for a given pathogen. Moreover, abiotic stresses can affect the timely expression of plant defense and pathogen virulence. Indeed, several studies have shown that variations in temperature, water and mineral nutrient availability impact plant defense gene expression. Virulence gene expression, known to be crucial for disease outbreak, is also affected by environmental conditions, potentially modifying existing pathosystems and paving the way for emerging pathogens. The present review summarizes the current knowledge on the impact of abiotic stress on biotic interactions at the transcriptional level in both the plant and the pathogen side of the interaction. We performed a meta-data analysis of four different combinations of abiotic and biotic stresses. 197 modulated genes were common to all four combinations, with a strong defense-related GO term enrichment. We also describe the multistress-specific responses of selected defense-related genes.info:eu-repo/semantics/publishe