1,721,012 research outputs found
DspA/E Contributes to apoplastic accumulation of ROS in non-host a-thaliana
No full textThe bacterium Erwinia amylovora is responsible for the fire blight disease of Maleae, which provokes necrotic symptoms on aerial parts. The pathogenicity of this bacterium in hosts relies on its type three-secretion system (T3SS), a molecular syringe that allows the bacterium to inject effectors into the plant cell. E. amylovora-triggered disease in host plants is associated with the T3SS-dependent production of reactive oxygen species (ROS), although ROS are generally associated with resistance in other pathosystems. We showed previously that E. amylovora can multiply transiently in the non-host plant Arabidopsis thaliana and that a T3SS-dependent production of intracellular ROS occurs during this interaction. In the present work we characterize the localization and source of hydrogen peroxide accumulation following E. arnylovora infection. Transmission electron microscope (TEM) analysis of infected tissues showed that hydrogen peroxide accumulation occurs in the cytosol, plastids, peroxisomes, and mitochondria as well as in the apoplast. Furthermore, TEM analysis showed that an E. amylovora dspA/E-deficient strain does not induce hydrogen peroxide accumulation in the apoplast. Consistently, a transgenic line expressing DspA/E accumulated ROS in the apoplast. The NADPH oxidase-deficient rbohD mutant showed a very strong reduction in hydrogen peroxide accumulation in response to E. amylovora inoculation. However, we did not find an increase in bacterial titers of E. amylovora in the rbohD mutant and the rbohD mutation did not suppress the toxicity of DspA/E when introgressed into a DspA/E-expressing transgenic line. Co-inoculation of E. amylovora with cycloheximide (CHX), which we found previously to suppress callose deposition and allow strong multiplication of E. amylovora in A. thaliana leaves, led to a strong reduction of apoplastic ROS accumulation but did not affect intracellular ROS. Our data strongly suggest that apoplastic ROS accumulation is one layer of the non-host defense response triggered by the type three effector (T3E) DspA/E, together with callose deposition
A bile acid elicits receptor-like kinase-dependent defenses in Arabidopsis and reduces bacterial infection
No full textLooking 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.
No full textLa 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Impact of nitrogen supply on the interactions of A. thaliana and bacterial phytopathogens
No full textL'azote (N) est l'un des principaux nutriments nécessaires pour la croissance des plantes et le rendement de cultures. Il est bien documenté que les changements dans la disponibilité du nitrate, principale source d’azote dans les sols agricoles, influent largement sur le processus de développement de la plante, y compris sur ses réponses de défense. La première partie de ce travail correspond à une analyse transcriptomique réalisée afin d’étudier les changements transcriptionnels au cours de l’infection d’A. thaliana par E. amylovora, dans les plantes cultivées à deux régimes de nutrition azotée (limitant ou non). L’analyse des données montre que, globalement, la réponse transcriptomique à la bactérie chez les plantes cultivées en azote limitant ou non est proche malgré la différence de développement de ces plantes. Malgré ces réponses globalement proches, des différences d’expression en réponse à l’infection ont été observés pour certaines voies de signalisation, notamment pour la voie de l’acide jasmonique. L’analyse de l’interaction entre les deux stress (N et bactérie) montre qu’en réponse à la combinaison des deux stress, 32.5% de gènes ont une réponse spécifique de la combinaison des stress, suggérant une interaction entre les réponses aux stresses simples. Parmi ces gènes, plusieurs sont liés à la défense contre les agents pathogènes, comme les facteurs de transcription de type WRKYs et les protéines de résistance. Dans la deuxième partie de ce travail, nous avons démontré l’effet de la disponibilité en azote sur l’expression des facteurs du pouvoir pathogène d’E. amylovora in planta. En effet, la bactérie E. amylovora se multiplie mieux dans des plantes cultivées à faible azote (2 mM NO3⁻) qu’à fort azote (10 mM NO3⁻). De plus, nous n’avions observé qu’un mutant affecté dans le pouvoir pathogène d’E. amylovora est aussi agressif que la souche sauvage dans des plantes cultivées à fort azote (10 mM NO3⁻), alors qu’on observe une différence d’agressivité entre les deux souches dans des plantes cultivées à faible azote (2 mM NO3⁻). Les expériences menées indiquent que l’effecteur de type 3 DspA/E, principal facteur du pouvoir pathogène d’E. amylovora, est significativement plus exprimé in planta à faible azote (2 mM NO3⁻) qu’à fort azote (10 mM NO3⁻). De plus, le niveau d’expression de ce facteur de virulence d’E. amylovora in planta est inversement corrélé avec l’expression des gènes de la voie de l’acide jasmonique PDF1.2 et JAR1. On a également observé une diminution de niveau des précurseurs chloroplastiques de l’acide jasmonique dans les plantes sensibles à Ea cultivées à faible N.Nitrogen (N) is one of the key nutrients needed for plant growth and crop yield. It is well documented that changes in the availability of nitrate, the main source of nitrogen in agricultural soils, greatly influence the process of plant development, including its defense responses.The first part of this work corresponds to a transcriptomic analysis, carried out in order to study the transcriptional changes during the infection of A. thaliana by E. amylovora, in plants grown under two nitrogen nutrition regimes (limiting or not). Analysis of the data shows that, generally, the transcriptomic response to the bacterium in plants grown in nitrogen limiting or not is close despite the difference in development of these plants. Despite these broadly similar responses, differences in expression in response to infection have been observed for some signaling pathways, notably for the jasmonic acid pathway. Analysis of the interaction between the two stresses (N and bacteria) shows that in response to the combination of the two stresses, 32.5% of genes have a specific response to stress combination, suggesting an interaction between simple stress responses. Among these genes, several are linked to defense against pathogens, such as WRKY transcription factors and resistance proteins.In the second part of this work, we demonstrated the effect of nitrogen availability on the expression of E. amylovora pathogenicity factors in planta. Indeed, bacteria multiplicated more in plants grown in low nitrogen (2 mM NO3⁻) than high nitrogen (10 mM NO3⁻). In addition, we only observed that mutant affected in the pathogenicity of E. amylovora is as aggressive as the wild-type strain in plants grown in high nitrogen (10 mM NO3⁻), while there is a difference in aggressiveness between the two strains in plants grown in low nitrogen (2 mM NO3⁻). The experiments indicate that the DspA / E effector, the main factor in the pathogenicity of E. amylovora, is significantly more expressed in planta at low nitrogen (2 mM NO3⁻) than at high nitrogen (10 mM NO3⁻). In addition, the level of expression of this virulence factor of E. amylovora in planta is inversely correlated with gene expression of the jasmonic acid pathway PDF1.2 and JAR1. Out results showed also a decrease in the level of chloroplastic precursors of jasmonic acid in susceptible plants to Ea grown in low N
- …
