Host-specific competitiveness to form nodules in Rhizobium leguminosarum symbiovar viciae

Fabeae legumes such as pea and faba bean form symbiotic nodules with a large diversity of soil Rhizobium leguminosarum symbiovar viciae (Rlv) bacteria. However, bacteria competitive to form root nodules (CFN) are generally not the most efficient to fix dinitrogen, resulting in a decrease in legume crop yields. Here, we investigate differential selection by host plants on the diversity of Rlv. A large collection of Rlv was collected by nodule trapping with pea and faba bean from soils at five European sites. Representative genomes were sequenced. In parallel, diversity and abundance of Rlv were estimated directly in these soils using metabarcoding. The CFN of isolates was measured with both legume hosts. Pea/faba bean CFN were associated to Rlv genomic regions. Variations of bacterial pea and/or faba bean CFN explained the differential abundance of Rlv genotypes in pea and faba bean nodules. No evidence was found for genetic association between CFN and variations in the core genome, but variations in specific regions of the nod locus, as well as in other plasmid loci, were associated with differences in CFN. These findings shed light on the genetic control of CFN in Rlv and emphasise the importance of host plants in controlling Rhizobium diversity

Sorbitol uptake is regulated by glucose through the hexokinase pathway in vegetative peach-tree buds

In peach trees (Prunus persica L. Batsch cv. Redhaven), sorbitol is a primary photosynthetic product and may play an important role in the budbreak process. Surprisingly, before budbreak (from January to early March), the concentration of sorbitol in the xylem sap decreases, while that of hexoses (glucose and fructose) increases. The aim of this work was to study the control of sorbitol uptake into vegetative buds by hexoses. Sorbitol uptake was selectively inhibited by hexoses at low and physiological concentrations and this effect was both reversible and concentration-dependent. In addition, the active uptake of sorbitol significantly declined in the plasma membrane vesicles-enriched fraction purified from glucose-treated vegetative buds, suggesting that the inhibitory action of glucose was at the membrane level. Finally, among several glucose analogues tested, only hexokinase substrates (2-deoxyglucose and mannose) were able to mimic the glucose effect, which was completely blocked by the hexokinase inhibitor mannoheptulose. These results represent the first steps towards a better understanding of polyol transport control in plants

Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses

Vegetative buds of peach (Prunus persica L. Batsch.) trees act as strong sinks and their bud break capacity can be profoundly affected by carbohydrate availability during the rest period (November-February). Analysis of xylem sap revealed seasonal changes in concentrations of sorbitol and hexoses (glucose and fructose). Sorbitol concentrations decreased and hexose concentrations increased with increasing bud break capacity. Sucrose concentration in xylem sap increased significantly but remained low. To clarify their respective roles in the early events of bud break, carbohydrate concentrations and uptake rates, and activities of NAD-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX) and cell wall invertase (CWI) were determined in meristematic tissues, cushion tissues and stem segments. Only CWI activity increased in meristematic tissues shortly before bud break. In buds displaying high bud break capacity (during January and February), concentrations of sorbitol and sucrose in meristematic tissues were almost unchanged, paralleling their low rates of uptake and utilization by meristematic tissues, and indicating that sorbitol and sucrose play a negligible role in the bud break process. Hexose concentrations in meristematic tissues and glucose imported by meristematic tissues correlated positively with bud break capacity, suggesting that hexoses are involved in the early events of bud break. These findings were confirmed by data for buds that were unable to break because they had been collected from trees deprived of cold. We therefore conclude that hexoses are of greater importance than sorbitol or sucrose in the early events of bud break in peach trees

Controlling the morphology of mesostructured silicas by pseudomorphic transformations: a route towards applications

International audienceMicelle-templated silicas (MTS) such as MCM-41 and MCM-48 feature unique textural properties owing to their uniform distribution of mesopores with tunable sizes. MTS synthesis is relevant to unique self-assembly processes between surfactants and inorganic matter. The properties of MTSs have been explored in view of applications in fields as diverse as catalysis, chromatography, sensing, photonics, optics, drug delivery, etc. The aim of this contribution is to review, and to highlight by new results, a synthesis strategy we have developed since 2002 to control the particle morphology of MTSs at the micro- to millimeter scale, a key step for transferring these materials from the state of beautiful artworks to applicable products. It is based on the concept of pseudomorphic suynthesis. éseudomorphism is well known in the mineral world. It allows preparation of a mineral with a morphology which is not related to its crystallographic symmetry group. The reuslting mineral assumes the outward crystal habit of a different mineral. This principle occurs at a nonconstant matter content by using a mineralization solution that exchanges anions (or cations) with an existing (preshaped) solid body, and allows the new structure to precipitate while maintaining the existing morphology. The comcept of pseudomorphic transformation is now applied to amorphous preshaped silica particles to produce MTSs with the same morphology, using an alkaline solution to dissolve the silica and repricipitate it around surfactant micelles into the ordered MTS structures. MTSs with hexagonal and cubic symmetry, different pore sizes, and controlled morphology have been synthesized. The new pseudomorphs have been successfully used as supports in chromatography, a very demanding application in terms of particle size and morphology

Glucose at physiological concentrations could regulate sorbitol transport into peach vegetative bud shortly before the bud break process

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Genetic bases of variation in plant architecture and rhizobial partner choice along the pea domestication gradient

International audienceLegumes play an increasingly important role in sustainable agriculture due to their ability to form a beneficial symbiotic interaction with nitrogen-fixing Rhizobium bacteria. Legumes are also a valuable source of protein for both feed and food, but are not grown as extensively as expected in Europe due to their high yield variability. Many genomic approaches are being developed to improve stress tolerance traits. However, to date, little attention has been paid to improving the interaction between symbiotic partners. The establishment of the symbiotic interaction is a complex evolutionary process in which the interests of both partners are not always aligned. No evidence was found in pea for co-selection of competitiveness for nodulation and nitrogen (N) fixation efficiency (Bourion et al., 2018). Furthermore, several data indicated that N fixation and plant growth could be suboptimal in fields where pea is exposed to populations of heterogenous rhizobial strains with contrasting effects on nodule, root and shoot development (Laguerre et al., 2007). We performed Genome-Wide Association Studies to decipher the genetic determinants and relationships between the complex trait of pea choice between rhizobial strains in mixture and plant architecture. A large panel of 340 pea accessions including very diverse cultivars, wild accessions and landraces, all inoculated with the same mixture of 28 diverse rhizobial strains, was grown in two successive experiments, on a high throughput non-destructive phenotyping platform. The proportion of each strain in the nodules of each pea at harvest was determined by DNA metabarcoding, and 20 variables of nodulated root architecture or plant growth traits were estimated by image analysis or measured. The results highlighted differential variation and largely uncoupled genetic bases between rhizobial partner choice and architectural or growth traits, along the pea domestication gradient

Les nouveaux discours publicitaires

Suite à la mutation des contextes sociomédiatiques et à l’épuisement de ses modèles traditionnels, la publicité s’est profondément renouvelée au tournant du XXIème siècle. Alors que les supports publicitaires se sont diversifiés avec le développement des médias électroniques, les stratégies publicitaires privilégient progressivement la promotion des marques au détriment des produits. Parallèlement, les publicités récentes tendent à brouiller leurs messages en les parasitant par des contenus a priori étrangers au marketing. Quant au langage publicitaire lui-même, il évolue de plus en plus vers le second degré et les pratiques métadiscursives en jouant avec la culture du public et les codes médiatiques.Cette livraison de Semen se propose de rendre compte des transformations proprement discursives des pratiques publicitaires depuis une quinzaine d’années, en s’intéressant aux répercussions que ces pratiques ont sur la dimension linguistique et iconique des annonces. En quoi les nouveaux discours publicitaires affectent-ils la rhétorique des messages commerciaux ? Quelles incidences ont-ils sur leur fonctionnement communicationnel ? Comment se concrétisent-ils dans la production des slogans, des textes et des images ?Réunissant neuf contributions de chercheurs provenant d’horizons divers (France, Suisse, Italie, Chili), ce numéro offre une réflexion approfondie sur les tendances publicitaires les plus actuelles, à travers leur diversité : stratégies dialogiques, pratiques intertextuelles, émergence de l’éthos des marques, dépublicitarisation, brand content, buzz, marketing viral, publicité ethnique

Les nouveaux discours publicitaires

Suite à la mutation des contextes sociomédiatiques et à l’épuisement de ses modèles traditionnels, la publicité s’est profondément renouvelée au tournant du XXIème siècle. Alors que les supports publicitaires se sont diversifiés avec le développement des médias électroniques, les stratégies publicitaires privilégient progressivement la promotion des marques au détriment des produits. Parallèlement, les publicités récentes tendent à brouiller leurs messages en les parasitant par des contenus a priori étrangers au marketing. Quant au langage publicitaire lui-même, il évolue de plus en plus vers le second degré et les pratiques métadiscursives en jouant avec la culture du public et les codes médiatiques.Cette livraison de Semen se propose de rendre compte des transformations proprement discursives des pratiques publicitaires depuis une quinzaine d’années, en s’intéressant aux répercussions que ces pratiques ont sur la dimension linguistique et iconique des annonces. En quoi les nouveaux discours publicitaires affectent-ils la rhétorique des messages commerciaux ? Quelles incidences ont-ils sur leur fonctionnement communicationnel ? Comment se concrétisent-ils dans la production des slogans, des textes et des images ?Réunissant neuf contributions de chercheurs provenant d’horizons divers (France, Suisse, Italie, Chili), ce numéro offre une réflexion approfondie sur les tendances publicitaires les plus actuelles, à travers leur diversité : stratégies dialogiques, pratiques intertextuelles, émergence de l’éthos des marques, dépublicitarisation, brand content, buzz, marketing viral, publicité ethnique

The competitiveness to form nodules shapes the capacities of <em>Rhizobium leguminosarum</em> sv viciae communities to promote symbiosis with specific hosts

National audienceCultivated fabeae legumes (pea, fababean, lentil) develop root nodules resulting from the symbiotic interaction with Rhizobium leguminosarum sv. viciae (Rlv). Individual Rlv bacteria are able to associate with various potential hosts, but in soil they are in mixture and they display a wide range of competitiveness to form nodules (CFN). Because in Rlv, CFN and capacity to fix nitrogen are genetically independent, CFN limits the effectiveness of inoculation strategies as efficient bacteria are often outcompeted by poorly efficient Rlv bacteria of the soil community. We developed a strategy to identify bacterial genes controlling CFN. A worldwide collection of 240 Rlv isolates was obtained by combining bacteria described in GenBank with new isolates obtained worldwide by pea, fababean and lentil root nodule trapping. 100 genomes (22 already in GenBank) were sequenced. The extended Rlv complex species includes probably 16 genospecies and two main groups of symbiosis plasmids that can be horizontally transferred. We identified phylogenetic clades of Rlv displaying contrasted levels of CFN upon pea and fababean. A molecular barcode was designed on nodD gene to discriminate and quantify intraspecific variability of Rlv in root systems allowing estimate CFN in symbiotic pea, fababean or lentil associations with multiple Rlv potential partners. Several plasmid regions genetically associated with pea/fababean CFN phenotypes were identified. Candidate genes include specific nod genes as well as other genes with unknown function in symbiosis