Transcriptome analysis of Sinorhizobium meliloti during symbiosis

BACKGROUND: Rhizobia induce the formation on specific legumes of new organs, the root nodules, as a result of an elaborated developmental program involving the two partners. In order to contribute to a more global view of the genetics underlying this plant-microbe symbiosis, we have mined the recently determined Sinorhizobium meliloti genome sequence for genes potentially relevant to symbiosis. We describe here the construction and use of dedicated nylon macroarrays to study simultaneously the expression of 200 of these genes in a variety of environmental conditions, pertinent to symbiosis. RESULTS: The expression of 214 S. meliloti genes was monitored under ten environmental conditions, including free-living aerobic and microaerobic conditions, addition of the plant symbiotic elicitor luteolin, and a variety of symbiotic conditions. Five new genes induced by luteolin have been identified as well as nine new genes induced in mature nitrogen-fixing bacteroids. A bacterial and a plant symbiotic mutant affected in nodule development have been found of particular interest to decipher gene expression at the intermediate stage of the symbiotic interaction. S. meliloti gene expression in the cultivated legume Medicago sativa (alfalfa) and the model plant M. truncatula were compared and a small number of differences was found. CONCLUSIONS: In addition to exploring conditions for a genome-wide transcriptome analysis of the model rhizobium S. meliloti, the present work has highlighted the differential expression of several classes of genes during symbiosis. These genes are related to invasion, oxidative stress protection, iron mobilization, and signaling, thus emphasizing possible common mechanisms between symbiosis and pathogenesis

Auxotrophy accounts for nodulation defect of most Sinorhizobium meliloti mutants in the branched-chain amino acid biosynthesis pathway

Some Sinorhizobium meliloti mutants in genes involved in isoleucine, valine, and leucine biosynthesis were previously described as being unable to induce nodule formation on host plants. Here, we present a reappraisal of the interconnection between the branched-chain amino acid biosynthesis pathway and the nodulation process in S. meliloti. We characterized the symbiotic phenotype of seven mutants that are auxotrophic for isoleucine, valine, or leucine in two closely related S. meliloti strains, 1021 and 2011. We showed that all mutants were similarly impaired for nodulation and infection of the Medicago sativa host plant. In most cases, the nodulation phenotype was fully restored by the addition of the missing amino acids to the plant growth medium. This strongly suggests that auxotrophy is the cause of the nodulation defect of these mutants. However, we confirmed previous findings that ilvC and ilvD2 mutants in the S. meliloti 1021 genetic background could not be restored to nodulation by supplementation with exogenous amino acids even though their Nod factor production appeared to be normal.Instituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Exacta

Simulateur de Production Solaire : un outil pédagogique innovant dédié à l’enseignement des principes fondamentaux de l’énergie photovoltaïque

Cet article décrit une nouvelle approche pédagogique pour l’enseignement des connaissances de base de l'énergie solaire et des applications photovoltaïques. Cette méthode d'enseignement expérimentale et interactive permet aux étudiants et aux concepteurs de systèmes photovoltaïques de manipuler un simulateur de production solaire. Cet outil de simulation reproduit à échelle réduite la trajectoire du soleil quelle que soit la période de l’année. La production d'énergie est ensuite calculée pour différentes inclinaisons et orientations d'un capteur solaire. Le simulateur offre aux étudiants l'occasion d'acquérir d’une façon ludique les fondamentaux de l’énergie photovoltaïque. Plusieurs exemples de travaux pratiques sont détaillés afin de donner une vue d'ensemble des exercices d'apprentissage qui pourraient être faits par les étudiants pour découvrir les multiples applications du photovoltaïque. À titre d’exemple, de nombreux cas d’études peuvent être traités tels que la mise en oeuvre des calculs de position du soleil, la caractérisation électrique des cellules solaires avec différentes technologies ou encore la programmation de suiveurs du point de puissance maximale

Auxotrophy accounts for nodulation defect of most Sinorhizobium meliloti mutants in the branched-chain amino acid biosynthesis pathway

Some Sinorhizobium meliloti mutants in genes involved in isoleucine, valine, and leucine biosynthesis were previously described as being unable to induce nodule formation on host plants. Here, we present a reappraisal of the interconnection between the branched-chain amino acid biosynthesis pathway and the nodulation process in S. meliloti. We characterized the symbiotic phenotype of seven mutants that are auxotrophic for isoleucine, valine, or leucine in two closely related S. meliloti strains, 1021 and 2011. We showed that all mutants were similarly impaired for nodulation and infection of the Medicago sativa host plant. In most cases, the nodulation phenotype was fully restored by the addition of the missing amino acids to the plant growth medium. This strongly suggests that auxotrophy is the cause of the nodulation defect of these mutants. However, we confirmed previous findings that ilvC and ilvD2 mutants in the S. meliloti 1021 genetic background could not be restored to nodulation by supplementation with exogenous amino acids even though their Nod factor production appeared to be normal.Instituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Exacta

Endosymbiotic Sinorhizobium meliloti modulate Medicago root susceptibility to secondary infection via ethylene

A complex network of pathways coordinates nodulation and epidermal root hair infection in the symbiotic interaction between rhizobia and legume plants. Whereas nodule formation was known to be autoregulated, it was so far unclear whether a similar control is exerted on the infection process. We assessed the capacity of Medicago plants nodulated by Sinorhizobium meliloti to modulate root susceptibility to secondary bacterial infection or to purified Nod factors in split-root and volatile assays using bacterial and plant mutant combinations. Ethylene implication in this process emerged from gas production measurements, use of a chemical inhibitor of ethylene biosynthesis and of a Medicago mutant affected in ethylene signal transduction. We identified a feedback mechanism that we named AOI (for Autoregulation Of Infection) by which endosymbiotic bacteria control secondary infection thread formation by their rhizospheric peers. AOI involves activation of a cyclic adenosine 30,50-monophosphate (cAMP) cascade in endosymbiotic bacteria, which decreases both root infectiveness and root susceptibility to bacterial Nod factors. These latter two effects are mediated by ethylene. AOI is a novel component of the complex regulatory network controlling the interaction between Sinorhizobium meliloti and its host plants that emphasizes the implication of endosymbiotic bacteria in fine-tuning the interaction

Experimental Evolution of a Plant Pathogen into a Legume Symbiont

Following acquisition of a rhizobial symbiotic plasmid, adaptive mutations in the virulence pathway allowed pathogenic Ralstonia solanacearum to evolve into a legume symbiont under plant selection

Fiabilité du réseau électrique

Le concept de fiabilité est de plus en plus utilisé dans le monde scientifique et technique. Que peut-il apporter au planificateur du système électrique ? Après avoir défini la fiabilité du système électrique, nous le situons dans le contexte de la planification, puis en exposons un cadre d'évaluation. Nous présentons ensuite les besoins du planificateur en la matière, en particulier pour l'évaluation de la fiabilité (méthode de calcul et données), et signalons enfin une possible rétroaction de la planification du système sur la conception des composants. Mots-Clés : Fiabilité - Planification - Système production-transport ďélectricité - Méthode de calcul - Données de fiabilité - Conception des composants.Batut Jacques. Fiabilité du réseau électrique. In: Cahier / Groupe Réseaux, n°9, 1987. pp. 33-42

Etudes structurales de plasmides de Rhizobium meliloti

CNRS T 55758 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Probabilistic design of power-system special stability controls

A probabilistic approach to the design of power-system special stability controls is presented here. Using Monte-Carlo simulations, it takes into account all the potential causes of blackouts, slow and fast dynamics, and modeling uncertainties. A large number of scenarios are simulated in parallel by time-domain numerical integration, and the relevant parameters of the resulting system trajectories are stored in a database. Data-mining tools are used to identify the most important system weaknesses and possible improvements. The approach is tested on a large-scale study on the SouthÐEastern part of the extra-high-voltage system of Electricité de France

IDENTIFICATION ET CARACTERISATION DE GENES DE SINORHIZOBIUM MELILOTI REGULES AU COURS DE L'INTERACTION SYMBIOTIQUE AVEC MEDICAGO SATIVA

SINORHIZOBIUM MELILOTI INDUIT SUR LES RACINES DE LA LUZERNE LA FORMATION D'ORGANES SPECIALISES DANS LA FIXATION DE L'AZOTE, LES NODOSITES. LE DEVELOPPEMENT DE CES NODOSITES NECESSITE L'EXPRESSION COORDONNEE DE NOMBREUX GENES VEGETAUX ET BACTERIENS. AFIN D'IDENTIFIER DE TELS GENES, POTENTIELLEMENT IMPORTANTS POUR L'ETABLISSEMENT DE LA SYMBIOSE, NOUS NOUS SOMMES INTERESSE AUX GENES BACTERIENS DONT L'EXPRESSION EST REGULEE DANS LES NODOSITES. NOUS AVONS ISOLE PAR RNA FINGERPRINTING BY ARBITRARILY PRIMED PCR 17 ADNC DIFFERENTIELLEMENT EXPRIMES EN CONDITIONS SYMBIOTIQUES PAR RAPPORT AUX CONDITIONS DE CULTURE PURE. 13 ADNC CORRESPONDENT A DES GENES REGULES POSITIVEMENT EN SYMBIOSE ALORS QUE 4 SONT REPRIMES EN CONDITIONS SYMBIOTIQUES. L'ANALYSE DETAILLEE DE L'EXPRESSION DES GENES CORRESPONDANTS NOUS A PERMIS DE METTRE EN EVIDENCE UNE VARIETE INSOUPCONNEE DE PROFILS DE REGULATION. 7 ADNC CORRESPONDENT A DES GENES NIF ET FIX CONNUS OU PREDITS. LES PRODUITS DE 4 ADNC PRESENTENT UNE FORTE SIMILARITE AVEC DES PROTEINES NON IDENTIFIEES CHEZ S. MELILOTI, A SAVOIR UN COMPOSANT DU COMPLEXE PYRUVATE DESHYDROGENASE, UNE PROTEINE DE SURFACE DE LA CELLULE, UN TRANSPORTEUR DE CUIVRE ET UNE ARGININOSUCCINATE LYASE. LES PRODUITS DES 6 AUTRES ADNC NE MONTRENT AUCUNE SIMILARITE AVEC DES PROTEINES CONNUES. UN DES ADNC CODE POUR UN DES COMPOSES DU COMPLEXE PYRUVATE DESHYDROGENASE, UN ELEMENT CLE DU METABOLISME CARBONE QUI CATALYSE LA FORMATION D'ACETYL-COA A PARTIR DE PYRUVATE. NOUS AVONS MONTRE QUE L'EXPRESSION DE PDHA EST TRES FORTEMENT INDUITE EN SYMBIOSE ET EST INDEPENDANTE DE LA CASCADE QUI REGULE LES GENES DE FIXATION DE L'AZOTE ET LES GENES DE RESPIRATION DE S. MELILOTI. L'EXPRESSION DE PDHA EST INDUITE EN CULTURE PURE PAR LE PYRUVATE. CETTE INDUCTION AINSI QUE L'ACTIVATION SYMBIOTIQUE DES GENES PDH ONT LIEU AU MEME PROMOTEUR. CES RESULTATS SUGGERENT UN ROLE ESSENTIEL DE LA PYRUVATE DESHYDROGENASE POUR LE METABOLISME BACTERIEN SYMBIOTIQUE ET UN ROLE REGULATEUR DU PYRUVATE EN SYMBIOSE.TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF