Le s symbioses fixatrices d’azote : types et régulateurs t ranscriptionnels de la nodulation

Les symbioses fixatrices d’azote sont des interactions à bénéfice réciproque entre certaines espèces végétales (légumineuses et plantes actinorhiziennes principalement) et des microorganismes du sol ( r hizobium ou Frankia ). Ces symbioses contribuent de façon considérable à la nutrition azotée de ces plantes e t donc à leur développement particulièrement sur l es sols pauvres en azote . L’établissement de ces symbioses démarre par un dialogue moléculaire , puis par la formation de structures appelées nodules ou nodosités , siège des échanges entre les deux partenaires (plante et bactérie) La formation et le développement de nodules requièrent la médiation de gènes spécifiques parmi les quels figurent les régulateurs transcriptionnels ( facteurs de transcription et microARN) microARN). Des facteurs de transcription dont CYCLOPS, NSP1 et NSP2 communs entre les symbioses r hizobium légumineuse et Frankia plante actinorhizienne ont été caractérisés à d ifférents stades du développement du nodule Ils interagissent avec les protéines DE LLA pour induire l’expression du gène NIN , n écessaire à l’initiation de l’infection . Ces facteurs de transcription sont régulés par divers microARN. Cette revue résume l es types de symbioses fixatrices d’azote et les récentes avancées sur l es régulateurs transcriptionnels impliqué s dans l es étapes de pré infection, d’infection et d’organogenèse du nodule . Pour ce faire, nous avons collecté et analysé des données pertinentes de la littérature sur des études moléculaires et cellulaires des symbioses fixatrices d’azote

The roots of future rice harvests

The authors thank the Global Rice Science Partnership and Agropolis Fondation (Special grant n° 1400–009 and Rhizopolis grant n° 1001–005) benefiting from a national ANR Investissement d’Avenir” grant ANR-10-LABX-001-01) for supporting the workshop. They acknowledge the assistance of Nathalie Pivot, Cirad and Véronique Rafin, INRA in workshop organization. The root research at Cirad and University of Aberdeen is supported by the European Grant (FP7/2007-2013) under grant agreement n° 289300.27 EURoot “Enhancing resource Uptake from ROOTs under stress in cereal crops”. Research at IRRI is supported by the Generation Challenge Program and the Bill and Melinda Gates Foundation. J.X. is supported by the AcRF Tier 2 grant (MOE2009-T2-1-060) from the Ministry of Education of Singapore and National Research Foundation Singapore under its Competitive Research Programme (CRP Award No. NRF2010 NRF-CRP002-018). Doan Trung Luu is supported by the EU Marie Curie International Outgoing Fellowship 'ORYZAQUA – Cell Biology of Rice Aquaporins' (PIOF-GA-2011-300150). AP acknowledges the Generation Challenge Programme funded project “Targeting drought avoidance root traits to enhance rice productivity under water limited environments”. Financial support for A.G. Diedhiou was provided by the Université Cheikh Anta Diop (UCAD, VE12/13, CpVIII-Ar4 ) and GRISP. *This paper is dedicated to the late memory of Pr Ping Wu who passed away in a tragic car accident on June 12th, 2014.Peer reviewedPublisher PD

Champignons ectomycorhiziens des forêts tropicales d'Afrique de l'Ouest (étude de la compétitivité et analyse de la diversité génétique)

MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Response of ectomycorrhizal communities to past Roman occupation in an oak forest

International audienc

The functional structure of ectomycorrhizal communities in an oak forest in central France witnesses ancient Gallo-Roman farming practices

Abbreviations Ce, cellobiohydrolase Chi, chitinase (n-acetyl glucosaminidase) Go, b-glucosidase Gu, glucuronidase La, laccase Le, leucine aminopeptidase Ph, acid phosphatase Xy, xylosidaseInternational audienceThe activities of nutrient-mobilising enzymes secreted by ectomycorrhizas of sessile oak (Quercus petraea) have been measured in 24 plots in a forested area in central France where many rural Gallo-Roman settlements (first to fifth centuries AD) have been discovered. Data have been related with tree growth and soil chemical properties. Although soil near the past settlements is still enriched in N and P, this does not always correspond to the higher productivity of oak trees. However, when this is the case, the ectomycorrhizal community displays higher chitinase, protease and phosphatase activities (involved in N and P mobilisation from soil organic matter). A few specialised ectomycorrhizal fungal species are responsible for this adaptation to the long-lasting modification of soil conditions

Rice developmental stages modulate rhizosphere bacteria and archaea co-occurrence and sensitivity to long-term inorganic fertilization in a West African Sahelian agro-ecosystem

Abstract Background Rhizosphere microbial communities are important components of the soil-plant continuum in paddy field ecosystems. These rhizosphere communities contribute to nutrient cycling and rice productivity. The use of fertilizers is a common agricultural practice in rice paddy fields. However, the long-term impact of the fertilizers usage on the rhizosphere microbial communities at different rice developmental stages remains poorly investigated. Here, we examined the effects of long-term (27 years) N and NPK-fertilization on bacterial and archaeal community inhabiting the rice rhizosphere at three developmental stages (tillering, panicle initiation and booting) in the Senegal River Delta. Results We found that the effect of long-term inorganic fertilization on rhizosphere microbial communities varied with the rice developmental stage, and between microbial communities in their response to N and NPK-fertilization. The microbial communities inhabiting the rice rhizosphere at panicle initiation appear to be more sensitive to long-term inorganic fertilization than those at tillering and booting stages. However, the effect of developmental stage on microbial sensitivity to long-term inorganic fertilization was more pronounced for bacterial than archaeal community. Furthermore, our data reveal dynamics of bacteria and archaea co-occurrence patterns in the rice rhizosphere, with differentiated bacterial and archaeal pivotal roles in the microbial inter-kingdom networks across developmental stages. Conclusions Our study brings new insights on rhizosphere bacteria and archaea co-occurrence and the long-term inorganic fertilization impact on these communities across developmental stages in field-grown rice. It would help in developing strategies for the successful manipulation of microbial communities to improve rice yields

Pairwise Transcriptomic Analysis of the Interactions Between the Ectomycorrhizal Fungus Laccaria bicolor S238N and Three Beneficial, Neutral and Antagonistic Soil Bacteria

Ectomycorrhizal fungi are surrounded by bacterial communities with which they interact physically and metabolically during their life cycle. These bacteria can have positive or negative effects on the formation and the functioning of ectomycorrhizae. However, relatively little is known about the mechanisms by which ectomycorrhizal fungi and associated bacteria interact. To understand how ectomycorrhizal fungi perceive their biotic environment and the mechanisms supporting interactions between ectomycorrhizal fungi and soil bacteria, we analysed the pairwise transcriptomic responses of the ectomycorrhizal fungus Laccaria bicolor (Basidiomycota: Agaricales) when confronted with beneficial, neutral or detrimental soil bacteria. Comparative analyses of the three transcriptomes indicated that the fungus reacted differently to each bacterial strain. Similarly, each bacterial strain produced a specific and distinct response to the presence of the fungus. Despite these differences in responses observed at the gene level, we found common classes of genes linked to cell–cell interaction, stress response and metabolic processes to be involved in the interaction of the four microorganisms

Réponse du fonio blanc (Digitaria exilis Stapf) à l’inoculation avec des champignons mycorhiziens à arbuscules en conditions semi-contrôlées

Objectif : Le fonio blanc (Digitaria exilis Stapf), malgré ses nombreuses qualités nutritionnelles et thérapeutiques, est considéré comme une culture négligée ou mineure dans plusieurs pays ouest-africains. Bien que le fonio, comme toute céréale s’associerait à des champignons mycorhiziens à arbuscules (CMA), aucune donnée n’a encore été publiée sur son statut mycorhizien. L’objectif de cette étude était de déterminer la dépendance mycorhizienne du fonio à l’inoculation avec des champignons mycorhiziens à arbuscules (CMA). Méthodologie et résultats: Une accession de fonio provenant de la région de Sédhiou (sud du Sénégal) a été inoculée avec sept espèces de CMA (Glomus aggregatum, G. fasciculatum, G. etunicatum, G. manihotis, G. mosseae, G. verriculosum et Rhizophagus irregularis). Un dispositif expérimental complètement aléatoire avec dix plants par traitement a été utilisé pour comparer les sept traitements inoculés avec les sept souches de CMA en conditions semi-contrôlées. Après 110 jours de culture, les paramètres de mycorhzation et de croissance ont été mesurés. Les résultats ont montré que les taux de mycorhization les plus élevés ont été obtenus avec G. aggregatum et R. irregularis alors que l’inoculation avec G. verriculosum, G. manihotis et R. irregularis a amélioré significativement la biomasse des plants de fonio. Des effets positifs significatifs de l’inoculation mycorhizienne ont également été observés en fonction des espèces de CMA avec des augmentations sur la biomasse totale (+14,44% à +45,56%), le tallage(+15,79% à 31,58% à l’exception de G. etunicatum, G. manihotis), la production de feuilles (+13,41% à +35,79%), de panicules (+20,70% à 39,24%) et de racèmes (+52,94% à +125,29%). Conclusion et application : Les résultats ont montré que le fonio répond bien à l’inoculation mycorhizienne avec cependant un degré de dépendance variable en fonction de l’espèce de CMA. Ceci suggère que l’utilisation de CMA comme biofertilisant pourrait constituer une stratégie prometteuse pour contribuer à l’amélioration de la productivité du fonio au Sénégal et dans d’autres pays ouest-africains.Mots clés : Fonio, champignons mycorhiziens arbusculaires, inoculation, conditions semi-contrôlée

Development of a model estimating root length density from root impacts on a soil profile in pearl millet (Pennisetum glaucum (L.) R. Br). Application to measure root system response to water stress in field conditions

International audiencePearl millet is able to withstand dry and hot conditions and plays an important role for food security in arid and semi-arid areas of Africa and India. However, low soil fertility and drought constrain pearl millet yield. One target to address these constraints through agricultural practices or breeding is root system architecture. In this study, in order to easily phenotype the root system in field conditions, we developed a model to predict root length density (RLD) of pearl millet plants from root intersection densities (RID) counted on a trench profile in field conditions. We identified root orientation as an important parameter to improve the relationship between RID and RLD. Root orientation was notably found to depend on soil depth and to differ between thick roots (more anisotropic with depth) and fine roots (isotropic at all depths). We used our model to study pearl millet root system response to drought and showed that pearl millet reorients its root growth toward deeper soil layers that retain more water in these conditions. Overall, this model opens ways for the characterization of the impact of environmental factors and management practices on pearl millet root system development