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Évolution paléogéographique et karstogenèse du bassin d'Issirac (Gard, France) du Crétacé supérieur au Miocène inférieur
No full textSince the emergence of the carbonated platform of the southeastern basin of France during the Albian-Cénomanian, a long process of complex polyphased karstification is being installed under joint influence of tectonics, eustatism and climate. The endorheic basin of Issirac includes terrains from Cretaceous until Eocene age. Connected to the Alès groove, it has been undergoing eustatic variations combined with flows coming at the same time from the Cevennes and, apparently, from the installing endokarst in the regional carbonated platform englobing the plateau of Méjannes-le-Clap, located in the north of the Gard department, and the Cèze-Ardèche interfluvium. These observations underline a karstogenesis going back to late Cretaceous and early Paleogene times, related to the installation of a basin in conjunction with a planation surface in and on which redesigned sediments have been deposed of which, at present time, only relics remain. Nevertheless its poor visibility at the level of Paleocene and Eocene terrains of the Issirac basin, the karstogenesis permits to observe in the underlying limestone levels of the late Barrémian and Aptian (Bédoulian), indications of excavation whose infillings show strong proportions of alterites containing minerals of volcanic or magmatic origin coming from the Central Massif. The development of karstic aquiphers is orienting hypogeous drains towards successive base levels installing into the endorheic basin during the same periods, before their accomodations during Oligocene and Miocene times. This dynamic is modeling new endokarstic shaping of various gradations. The most recent geological in situ observations are indicating a progressive inversion of hypogeous drains changing from sedimentary base level aggradations formed by the endorheic basin of Issirac towards those of successive low levels related to the incision of Cèze and Ardèche rivers during Cenozoïc eras.Depuis l'émersion de la plate-forme carbonatée du bassin du Sud-Est de la France à l'époque de l'Albien-Cénomanien, un long processus de karstification complexe et polyphasé se met en place, sous les contraintes conjointes de la tectonique, de l'eustatisme et du climat. Le bassin endoréique d'Issirac comprend des terrains allant du Crétacé à l'Éocène. Connecté au sillon d'Alès, il a été soumis à des variations eustatiques combinées à des écoulements provenant à la fois des Cévennes et vraisemblablement de l'endokarst en cours d'édification dans la plate-forme carbonatée régionale qui englobe le plateau de Méjannes-le-Clap, situé au nord du département du Gard, et l'interfluve Cèze-Ardèche. Une karstogenèse s'instaure au Crétacé supérieur et au début du Paléogène. Elle est liée à l'installation d'un bassin et la formation d'une surface d'aplanissement où se déposent des sédiments remaniés dont il ne reste à ce jour que des reliquats. Peu visible au niveau des formations du Paléocène et de l'Éocène du bassin d'Issirac, la karstogenèse laisse entrevoir dans les assises calcaires du Barrémien supérieur et de l'Aptien (Bédoulien), des indices de creusement dont les remplissages contiennent en forte proportion des altérites présentant de minéraux d'origine volcanique ou magmatique en provenance du Massif Central. L'élaboration d'aquifères karstiques oriente des écoulements hypogés dirigés en premier lieu vers les niveaux de base successifs s'établissant dans le bassin endoréique au cours des mêmes périodes puis leurs accommodations au cours de l'Oligocène et du Miocène. Cette dynamique modèle des nouveaux façonnements endokarstiques de diverses ampleurs. Les dernières observations géologiques in situ mettent en exergue un changement de direction progressif des écoulements hypogés passant ainsi des aggradations sédimentaires du niveau de base constitué par le bassin endoréique d'Issirac à des points bas successifs liés à l'enfoncement des cours d'eau de la Cèze et de l'Ardèche durant l'ère Cénozoïque
Conjugacy class of homeomorphisms and distortion elements in groups of homeomorphisms
No full textLet S be a compact connected surface and let f be an element of the group Homeo_0(S) of homeomorphisms of S isotopic to the identity. Denote by \tilde{f} a lift of f to the universal cover of S. Fix a fundamental domain D of this universal cover. The homeomorphism f is said to be non-spreading if the sequence (d_{n}/n) converges to 0, where d_{n} is the diameter of \tilde{f}^{n}(D). Let us suppose now that the surface S is orientable with a nonempty boundary. We prove that, if S is different from the annulus and from the disc, a homeomorphism is non-spreading if and only if it has conjugates in Homeo_{0}(S) arbitrarily close to the identity. In the case where the surface S is the annulus, we prove that a homeomorphism is non-spreading if and only if it has conjugates in Homeo_{0}(S) arbitrarily close to a rotation (this was already known in most cases by a theorem by Béguin, Crovisier, Le Roux and Patou). We deduce that, for such surfaces S, an element of Homeo_{0}(S) is distorted if and only if it is non-spreading
Ecological impact of a secondary bacterial symbiont on the clones of Sitobion avenae (Fabricius) (Hemiptera: Aphididae)
No full textMany insects harbor heritable endosymbionts, whether obligatory or facultative, and the role of facultative endosymbionts in shaping the phenotype of these species has become increasingly important. However, little is known about whether micro-injected endosymbionts can have any effects on aphid clones, which was measured using various ecological parameters. We examined the effects between symbiotic treatments and the vital life history traits generated by Regiella insecticola on the life table parameters of Sitobion avenae. The results showed that R. insecticola can decrease the intrinsic rate of increase (r), the finite rate of increase (lambda) and birth rate and can increase the mean generation times (T) of S. avenae clones, suggesting that R. insecticola may decelerate the normal development of the hosts. No significant differences of these parameters were observed between the examined Sitobion avenae clones, and the symbiont treatment by genotype interaction affected only the net reproduction rate R-0, pre-adult duration and total longevity but not the other parameters. Additionally, a population projection showed that R. insecticola decelerated the growth of the S. avenae clones. The evocable effects of R. insecticola on the S. avenae clones may have significant ramifications for the control of S. avenae populations under field/natural conditions
Cytokinins in Symbiotic Nodulation: When, Where, What For?
No full textSubstantial progress has been made in the understanding of early stages of the symbiotic interaction between legume plants and rhizobium bacteria. Those include the specific recognition of symbiotic partners, the initiation of bacterial infection in root hair cells, and the inception of a specific organ in the root cortex, the nodule. Increasingly complex regulatory networks have been uncovered in which cytokinin (CK) phytohormones play essential roles in different aspects of early symbiotic stages. Intriguingly, these roles can be either positive or negative, cell autonomous or non-cell autonomous, and vary, depending on time, root tissues, and possibly legume species. Recent developments on CK symbiotic functions and interconnections with other signaling pathways during nodule initiation are the focus of this review
Advances on plant-pathogen interactions from molecular toward systems biology perspectives
No full textautre Projet Européen : 3334036, SEPARATE Identification of Sclerotinia sclerotiorum Effector Proteins mediating virulence on Arabidopsis thaliana ecotypesIn the past 2 decades, progress in molecular analyses of the plant immune system has revealed key ele-ments of a complex response network. Current paradigms depict the interaction of pathogen-secreted mole-cules with host target molecules leading to the activation of multiple plant response pathways. Furtherresearch will be required to fully understand how these responses are integrated in space and time, andexploit this knowledge in agriculture. In this review, we highlight systems biology as a promising approachto reveal properties of molecular plant–pathogen interactions and predict the outcome of such interactions.We first illustrate a few key concepts in plant immunity with a network and systems biology perspective.Next, we present some basic principles of systems biology and show how they allow integrating multi-omics data and predict cell phenotypes. We identify challenges for systems biology of plant–pathogen inter-actions, including the reconstruction of multiscale mechanistic models and the connection of host andpathogen models. Finally, we outline studies on resistance durability through the robustness of immunesystem networks, the identification of trade-offs between immunity and growth and in silico plant–patho-gen co-evolution as exciting perspectives in the field. We conclude that the development of sophisticatedmodels of plant diseases incorporating plant, pathogen and climate properties represent a major challengefor agriculture in the future
Advances in pyramiding resistance genes to root-knot nematodes in Prunus rootstocks
No full textAdvances in pyramiding resistance genes to root-knot nematodes in Prunus rootstocks. 9. International Peach symposiumH
HpaB-Dependent Secretion of Type III Effectors in the Plant Pathogens Ralstonia solanacearum and Xanthomonas campestris pv. vesicatoria
No full textPlant pathogenic bacteria exerts their pathogenicity through the injection of large repertoires of type III effectors (T3Es) into plant cells, a mechanism controlled in part by type III chaperones (T3Cs). In Ralstonia solanacearum, the causal agent of bacterial wilt, little is known about the control of type III secretion at the post-translational level. Here, we provide evidence that the HpaB and HpaD proteins do act as bona fide R. solanacearum class IB chaperones that associate with several T3Es. Both proteins can dimerize but do not interact with each other. After screening 38 T3Es for direct interactions, we highlighted specific and common interacting partners, thus revealing the first picture of the R. solanacearum T3C-T3E network. We demonstrated that the function of HpaB is conserved in two phytopathogenic bacteria, R. solanacearum and Xanthomonas campestris pv. vesicatoria (Xcv). HpaB from Xcv is able to functionally complement a R. solanacearum hpaB mutant for hypersensitive response elicitation on tobacco plants. Likewise, Xcv is able to translocate a heterologous T3E from R. solanacearum in an HpaB-dependent manner. This study underlines the central role of the HpaB class IB chaperone family and its potential contribution to the bacterial plasticity to acquire and deliver new virulence factors
OAD Serre : Développement d’outils d'aide à la décision en cultures horticoles sous serres : vers une horticulture de précision
No full textprésentaté lors du Colloque Casdar 2017Conventional crop protection is reaching its limits through the inefficacy of the products and the unintended impacts on the environment. Integrated protection, using in particular auxiliaries, nevertheless depends on the development of reliable methods for estimating population densities of pests and auxiliaries. From a tool already partially developed for research, the Sophia@datamarket (S@M), a decision support tool dedicated to the horticultural profession was designed. Modules for the monitoring of the crop - the overall monitoring of pests and auxiliaries - have been developed. The design of tools for visual representation of epidemics or the distribution of auxiliaries and their dynamics over time facilitates decision-making. The development of new modules is continuing and the tool is tested on other crops in the framework of other partnership projects.La protection des cultures selon les moyens conventionnels trouve aujourd’hui ses limites, par l’inefficacité des produits phytopharmaceutiques et aux impacts non intentionnels engendrés sur l’environnement. La protection intégrée utilisant notamment des auxiliaires reste toutefois conditionnée au développement de méthodes fiables d'estimation des densités de populations de ravageurs et d'auxiliaires. A partir d’un outil déjà partiellement développé pour la recherche, le Sophia@datamarket (S@M), un outil d'assistance à la décision dédié à la profession horticole a été conçu. Des modules permettant le monitoring de la culture - le suivi global de l'ensemble des ravageurs et auxiliaires - ont été développés. La conception d'outils de représentation visuelle des épidémies ou de la répartition des auxiliaires et leurs dynamiques dans le temps facilite la prise de décision. Le développement de nouveaux modules se poursuit et l’outil est testé sur d’autres cultures dans le cadre d’autres projets partenariaux
Improved methods and resources for paramecium genomics: transcription units, gene annotation and gene expression
No full textBackground: The 15 sibling species of the Paramecium aurelia cryptic species complex emerged after a whole genome duplication that occurred tens of millions of years ago. Given extensive knowledge of the genetics and epigenetics of Paramecium acquired over the last century, this species complex offers a uniquely powerful system to investigate the consequences of whole genome duplication in a unicellular eukaryote as well as the genetic and epigenetic mechanisms that drive speciation. High quality Paramecium gene models are important for research using this system. The major aim of the work reported here was to build an improved gene annotation pipeline for the Paramecium lineage. Results: We generated oriented RNA-Seq transcriptome data across the sexual process of autogamy for the model species Paramecium tetraurelia. We determined, for the first time in a ciliate, candidate P. tetraurelia transcription start sites using an adapted Cap-Seq protocol. We developed TrUC, multi-threaded Perl software that in conjunction with TopHat mapping of RNA-Seq data to a reference genome, predicts transcription units for the annotation pipeline. We used EuGene software to combine annotation evidence. The high quality gene structural annotations obtained for P. tetraurelia were used as evidence to improve published annotations for 3 other Paramecium species. The RNA-Seq data were also used for differential gene expression analysis, providing a gene expression atlas that is more sensitive than the previously established microarray resource. Conclusions: We have developed a gene annotation pipeline tailored for the compact genomes and tiny introns of Paramecium species. A novel component of this pipeline, TrUC, predicts transcription units using Cap-Seq and oriented RNA-Seq data. TrUC could prove useful beyond Paramecium, especially in the case of high gene density. Accurate predictions of 3 ' and 5 ' UTR will be particularly valuable for studies of gene expression (e.g. nucleosome positioning, identification of cis regulatory motifs). The P. tetraurelia improved transcriptome resource, gene annotations for P. tetraurelia, P. biaurelia, P. sexaurelia and P. caudatum, and Paramecium-trained EuGene configuration are available through ParameciumDB (http://paramecium.i2bc.paris-saclay.fr). TrUC software is freely distributed under a GNU GPL v3 licence (https://github.com/oarnaiz/TrUC)
Nod factors potentiate auxin signaling for transcriptional regulation and lateral root formation in Medicago truncatula
No full textNodulation (Nod) factors (NFs) are symbiotic molecules produced by rhizobia that are essential for establishment of the rhizobium-legume endosymbiosis. Purified NFs can stimulate lateral root formation (LRF) in Medicago truncatula, but little is known about the molecular mechanisms involved. Using a combination of reporter constructs, pharmacological and genetic approaches, we show that NFs act on early steps of LRF in M. truncatula, independently of the ethylene signaling pathway and of the cytokinin receptor MtCRE1, but in interaction with auxin. We conducted a whole-genome transcriptomic study upon NF and/or auxin treatments, using a lateral root inducible system adapted for M. truncatula. This revealed a large overlap between NF and auxin signaling and, more interestingly, synergistic interactions between these molecules. Three groups showing interaction effects were defined: group 1 contained more than 1500 genes responding specifically to the combinatorial treatment of NFs and auxin; group 2 comprised auxin-regulated genes whose expression was enhanced or antagonized by NFs; and in group 3 the expression of NF regulated genes was antagonized by auxin. Groups 1 and 2 were enriched in signaling and metabolic functions, which highlights important crosstalk between NF and auxin signaling for both developmental and symbiotic processes