Rôle des Escherichia coli producteurs de cytotoxines dans la diarrhée du veau

Escherichia coli peut produire des cytotoxines (Verotoxines, Cytotoxic Necrotizing Factors, Cytolethal Distending Toxins) qui induisent des modifications caractéristiques chez des lignées cellulaires en culture. Ces colibacilles sont impliqués dans de graves pathologies à point de départ digestif, chez l'Homme et les Porcins notamment. Après une revue des éléments mettant en relief le pouvoir pathogène de ces colibacilles, l'auteur présente les résultats d'une enquête étiologique réalisée chez des veaux issus d'élevages de la région Bourgogne. L'étude compare des veaux sains et diarrhéiques âgés de moins d'un mois. Des souches d'E. coli isolées de leurs fèces sont analysées par différentes technique détectant les cytotoxines et leurs gènes, afin de déterminer si ces colibacilles sont présents et s'ils peuvent avoir une incidence sur les diarrhées observées. Si ces colibacilles sont effectivement rencontrés chez un tiers des veaux, il n'est pas possible de mettre en évidence une relation claire entre leur présence et la diarrhée des jeunes bovins. Ce types d'enquête cas-témoins n'est sans doute pas le moyen le plus adéquat pour démontrer la pathogénicité de ces germes sur le terrain

Auxin fluxes in the root apex co-regulate gravitropism and lateral root initiation

International audienceRoot architecture plays an important role in water and nutrient acquisition and in the ability of the plant to adapt to the soil. Lateral root development is the main determinant of the shape of the root system and is controlled by external factors such as nutrient concentration. Here it is shown that lateral root initiation and root gravitropism, two processes that are regulated by auxin, are co-regulated in Arabidopsis. A mathematical model was generated that can predict the effects of gravistimulations on lateral root initiation density and suggests that lateral root initiation is controlled by an inhibitory fields mechanism. Moreover, gene transactivation experiments suggest a mechanism involving a single auxin transport route for both responses. Finally, co-regulation may offer a selective advantage by optimizing soil exploration as supported by a simple quantitative analysis

Modeling auxin fluxes and Arabidopsis root ramification at different scales

International audienceno abstrac

Harvesting Plant and Microbial Biodiversity for Sustainably Enhanced Food Security

According to the United Nations, the World population will reach 9 billion by 2050, with the majority of this growth occurring in developing countries. More than half of global population growth is expected to occur in Africa. On the other hand, one in nine of the World’s population suffers from chronic hunger, the vast majority of which live in developing countries (FAO et al., 2015). We therefore need to find new and sustainable solutions to feed this increasing population and alleviate the predicted negative impact of global changes on crop production. This e-Book summarize current research to improve food security and livelihoods in rural communities, reduce vulnerability, increase resilience, and mitigate land degradation in developing countries..

Symbiotic Performance of Diverse Frankia Strains on Salt-Stressed Casuarina glauca and Casuarina equisetifolia Plants

Symbiotic nitrogen-fixing associations between Casuarina trees and the actinobacteria Frankia are widely used in agroforestry in particular for salinized land reclamation. The aim of this study was to analyze the effects of salinity on the establishment of the actinorhizal symbiosis between C. glauca and two contrasting Frankia strains (salt sensitive; CcI3 vs. salt tolerant; CeD) and the role of these isolates in the salt tolerance of C. glauca and C. equisetifolia plants. We show that the number of root nodules decreased with increasing salinity levels in both plants inoculated with CcI3 and CeD. Nodule formation did not occur in seedlings inoculated with CcI3 and CeD, at NaCl concentrations above 100 and 200 mM, respectively. Salinity also affected the early deformation of plant root hairs and reduced their number and size. In addition, expression of symbiotic marker Cg12 gene, which codes for a subtilase, was reduced at 50 mM NaCl. These data suggest that the reduction of nodulation in C. glauca under salt stress is in part due to inhibition of early mechanisms of infection. We also show that prior inoculation of C. glauca and C. equisetifolia with Frankia strains CcI3 and CeD significantly improved plant height, dry biomass, chlorophyll and proline contents at all levels of salinity tested, depending on the Casuarina-Frankia association. There was no correlation between in vitro salt tolerance of Frankia strains and efficiency in planta under salt-stressed conditions. Our results strongly indicate that increased N nutrition, photosynthesis potential and proline accumulation are important factors responsible for salt tolerance of nodulated C. glauca and C. equisetifolia

The role of hydraulics FSPMs in the context of root breeding : a case study on Pearl Millet

Developing a sustainable agricultural model is one of the great challenges of the coming years. The agricultural practices inherited from the Green Revolution of the 1960s show their limits today, and new paradigms need to be explored in the context of counter rising issues such as the multiplication of climate-change related drought episodes. Two such new paradigms are the use of functional-structural plant models to complement and rationalize breeding approaches and a renewed focus on root systems as untapped sources of plant improvement. Since the late 1980s, numerous functional and structural models of root systems were developed and used to investigate the properties of root systems in soil or lab-conditions. In this talk, we present a review on the use of multiscale functional-structural hydraulic root models in the context of drought tolerance breeding. We discuss how root models predictions can be linked to breeding studies to improve plant resistance to drought and how they can be validated to demonstrate models reliability and use. To illustrate this topic, we present a new structural model of pearl millet root system growth dynamics, combining stochastic and data-driven modules. The model is capable of simulating the development of observed root phenotypic variability of two millet genotypes chosen for their contrasted root traits. Model description, principle, assumptions, formalism and simulations will be presented during the talk

Experimental evidence of strong phonon scattering in isotopical disordered systems: The case of LiH_xD_{1-x} crystals

The observation of the local - mode vibration, the two - mode behavior of the LO phonons at large isotope concentration, as well as large line broadening in LIH - D mixed crystals directly evidence strong additional phonon scattering due to the isotope - induced disorder.Comment: 9 pages, 4 figure

Actinorhizal nitrogen fixing nodules: infection process, molecular biology and genomics

Actinorhizal hosts are non-leguminous perennial plants belonging to 8 angiosperm families. They are capable of forming root nodules as a result of infection by a nitrogen-fixing actinomycete called Frankia. Actinorhizal nodules consist of multiple lobes, each of which represents a modified lateral root with infected cells in the expanded cortex. This article summarizes the most recent knowledge about this original symbiotic process. The infection process is described both at cytological and molecular levels. The use of transgenic Casuarinaceae for studying in actinorhizal nodules the regulation of several symbiotic promoters from legumes is also discussed. With progress in plant genome sequencing, comparative genomics in legumes and actinorhizal plants should contribute to the understanding of the evolutionary history of nitrogen-fixing symbioses. Key words : Nitrogen-fixation, actinorhizal nodules, Frankia, Casuarina, symbiotic gene. African Journal of Biotechnology Vol. 2 (12), pp. 528-538, December 200

Heart of endosymbioses : transcriptomics reveals a conserved genetic program among arbuscular mycorrhizal, actinorhizal and legume-rhizobial symbioses

To improve their nutrition, most plants associate with soil microorganisms, particularly fungi, to form mycorrhizae. A few lineages, including actinorhizal plants and legumes are also able to interact with nitrogen-fixing bacteria hosted intracellularly inside root nodules. Fossil and molecular data suggest that the molecular mechanisms involved in these root nodule symbioses (RNS) have been partially recycled from more ancient and widespread arbuscular mycorrhizal (AM) symbiosis. We used a comparative transcriptomics approach to identify genes involved in establishing these 3 endosymbioses and their functioning. We analysed global changes in gene expression in AM in the actinorhizal tree C. glauca. A comparison with genes induced in AM in Medicago truncatula and Oryza sativa revealed a common set of genes induced in AM. A comparison with genes induced in nitrogen-fixing nodules of C. glauca and M. truncatula also made it possible to define a common set of genes induced in these three endosymbioses. The existence of this core set of genes is in accordance with the proposed recycling of ancient AM genes for new functions related to nodulation in legumes and actinorhizal plants

Inference of the Arabidopsis Lateral Root Gene Regulatory Network Suggests a Bifurcation Mechanism That Defines Primordia Flanking and Central Zones

A large number of genes involved in lateral root (LR) organogenesis have been identified over the last decade using forward and reverse genetic approaches in Arabidopsis thaliana. Nevertheless, how these genes interact to form a LR regulatory network largely remains to be elucidated. In this study, we developed a time-delay correlation algorithm (TDCor) to infer the gene regulatory network (GRN) controlling LR primordium initiation and patterning in Arabidopsis from a time-series transcriptomic data set. The predicted network topology links the very early-activated genes involved in LR initiation to later expressed cell identity markers through a multistep genetic cascade exhibiting both positive and negative feedback loops. The predictions were tested for the key transcriptional regulator AUXIN RESPONSE FACTOR7 node, and over 70% of its targets were validated experimentally. Intriguingly, the predicted GRN revealed a mutual inhibition between the ARF7 and ARF5 modules that would control an early bifurcation between two cell fates. Analyses of the expression pattern of ARF7 and ARF5 targets suggest that this patterning mechanism controls flanking and central zone specification in Arabidopsis LR primordia