78 research outputs found
Viral cystatin evolution and three-dimensional structure modelling: A case of directional selection acting on a viral protein involved in a host-parasitoid interaction
<p>Abstract</p> <p>Background</p> <p>In pathogens, certain genes encoding proteins that directly interact with host defences coevolve with their host and are subject to positive selection. In the lepidopteran host-wasp parasitoid system, one of the most original strategies developed by the wasps to defeat host defences is the injection of a symbiotic polydnavirus at the same time as the wasp eggs. The virus is essential for wasp parasitism success since viral gene expression alters the immune system and development of the host. As a wasp mutualist symbiont, the virus is expected to exhibit a reduction in genome complexity and evolve under wasp phyletic constraints. However, as a lepidopteran host pathogenic symbiont, the virus is likely undergoing strong selective pressures for the acquisition of new functions by gene acquisition or duplication. To understand the constraints imposed by this particular system on virus evolution, we studied a polydnavirus gene family encoding cyteine protease inhibitors of the cystatin superfamily.</p> <p>Results</p> <p>We show that <it>cystatins </it>are the first bracovirus genes proven to be subject to strong positive selection within a host-parasitoid system. A generated three-dimensional model of <it>Cotesia congregata </it>bracovirus cystatin 1 provides a powerful framework to position positively selected residues and reveal that they are concentrated in the vicinity of actives sites which interact with cysteine proteases directly. In addition, phylogenetic analyses reveal two different <it>cystatin </it>forms which evolved under different selective constraints and are characterized by independent adaptive duplication events.</p> <p>Conclusion</p> <p>Positive selection acts to maintain <it>cystatin </it>gene duplications and induces directional divergence presumably to ensure the presence of efficient and adapted cystatin forms. Directional selection has acted on key cystatin active sites, suggesting that cystatins coevolve with their host target. We can strongly suggest that cystatins constitute major virulence factors, as was already proposed in previous functional studies.</p
Genomic dissection of an extended phenotype:Oak galling by a cynipid gall wasp
Galls are plant tissues whose development is induced by another organism for the inducer's benefit. 30,000 arthropod species induce galls, and in most cases the inducing effectors and target plant systems are unknown. Cynipid gall wasps are a speciose monophyletic radiation that induce structurally complex galls on oaks and other plants. We used a model system comprising the gall wasp Biorhiza pallida and the oak Quercus robur to characterise inducer and host plant gene expression at defined stages through the development of galled and ungalled plant tissues, and tested alternative hypotheses for the origin and type of galling effectors and plant metabolic pathways involved. Oak gene expression patterns diverged markedly during development of galled and normal buds. Young galls showed elevated expression of oak genes similar to legume root nodule Nod factor-induced early nodulin (ENOD) genes and developmental parallels with oak buds. In contrast, mature galls showed substantially different patterns of gene expression to mature leaves. While most oak transcripts could be functionally annotated, many gall wasp transcripts of interest were novel. We found no evidence in the gall wasp for involvement of third-party symbionts in gall induction, for effector delivery using virus-like-particles, or for gallwasp expression of genes coding for plant hormones. Many differentially and highly expressed genes in young larvae encoded secretory peptides, which we hypothesise are effector proteins exported to plant tissues. Specifically, we propose that host arabinogalactan proteins and gall wasp chitinases interact in young galls to generate a somatic embryogenesis-like process in oak tissues surrounding the gall wasp larvae. Gall wasp larvae also expressed genes encoding multiple plant cell wall degrading enzymes (PCWDEs). These have functional orthologues in other gall inducing cynipids but not in figitid parasitoid sister groups, suggesting that they may be evolutionary innovations associated with cynipid gall induction
Death and the Societies of Late Antiquity
Ce volume bilingue, comprenant un ensemble de 28 contributions disponibles en français et en anglais (dans leur version longue ou abrĂ©gĂ©e), propose dâĂ©tablir un Ă©tat des lieux des rĂ©flexions, recherches et Ă©tudes conduites sur le fait funĂ©raire Ă lâĂ©poque tardo-antique au sein des provinces de lâEmpire romain et sur leurs rĂ©gions limitrophes, afin dâouvrir de nouvelles perspectives sur ses Ă©volutions possibles. Au cours des trois derniĂšres dĂ©cennies, les transformations considĂ©rables des mĂ©thodologies dĂ©ployĂ©es sur le terrain et en laboratoire ont permis un renouveau des questionnements sur les populations et les pratiques funĂ©raires de lâAntiquitĂ© tardive, pĂ©riode marquĂ©e par de multiples changements politiques, sociaux, dĂ©mographiques et culturels. Lâapparition de ce qui a Ă©tĂ© initialement dĂ©signĂ© comme une « Anthropologie de terrain », qui fut le dĂ©but de la dĂ©marche archĂ©othanatologique, puis le rĂ©cent dĂ©veloppement dâapproches collaboratives entre des domaines scientifiques divers (archĂ©othanatologie, biochimie et gĂ©ochimie, gĂ©nĂ©tique, histoire, Ă©pigraphie par exemple) ont Ă©tĂ© dĂ©cisives pour le renouvellement des problĂ©matiques dâĂ©tude : rĂ©vision dâanciens concepts comme apparition dâaxes dâanalyse inĂ©dits. Les recherches rassemblĂ©es dans cet ouvrage sont articulĂ©es autour de quatre grands thĂšmes : lâĂ©volution des pratiques funĂ©raires dans le temps, lâidentitĂ© sociale dans la mort, les ensembles funĂ©raires en transformation (organisation et topographie) et les territoires de lâempire (du cĆur aux marges). Ces Ă©tudes proposent un rĂ©examen et une rĂ©vision des donnĂ©es, tant anthropologiques quâarchĂ©ologiques ou historiques sur lâAntiquitĂ© tardive, et rĂ©vĂšlent, Ă cet Ă©gard, une mosaĂŻque de paysages politiques, sociaux et culturels singuliĂšrement riches et complexes. Elles accroissent nos connaissances sur le traitement des dĂ©funts, lâemplacement des aires funĂ©raires ou encore la structure des sĂ©pultures, en rĂ©vĂ©lant une diversitĂ© de pratiques, et permettent au final de relancer la rĂ©flexion sur la maniĂšre dont les sociĂ©tĂ©s tardo-antiques envisagent la mort et sur les Ă©lĂ©ments permettant dâidentifier et de dĂ©finir la diversitĂ© des groupes qui les composent. Elles dĂ©montrent ce faisant que nous pouvons vĂ©ritablement apprĂ©hender les structures culturelles et sociales des communautĂ©s anciennes et leurs potentielles transformations, Ă partir de lâĂ©tude des pratiques funĂ©raires.This bilingual volume proposes to draw up an assessment of the recent research conducted on funerary behavior during Late Antiquity in the provinces of the Roman Empire and on their borders, in order to open new perspectives on its possible developments. The considerable transformations of the methodologies have raised the need for a renewal of the questions on the funerary practices during Late Antiquity, a period marked by multiple political, social, demographic and cultural changes. The emergence field anthropology, which was the beginning of archaeothanatology, and then the recent development of collaborative approaches between various scientific fields (archaeothanatology, biochemistry and geochemistry, genetics, history, epigraphy, for example), have been decisive. The research collected in this book is structured around four main themes: Evolution of funerary practices over time; Social identity through death; Changing burial grounds (organisation and topography); Territories of the Empire (from the heart to the margins). These studies propose a review and a revision of the data, both anthropological and archaeological or historical on Late Antiquity, and reveal a mosaic of political, social, and cultural landscapes singularly rich and complex. In doing so, they demonstrate that we can truly understand the cultural and social structures of ancient communities and their potential transformations, based on the study of funerary practices
A genomically tractable and ecologically relevant model herbivore for a model plant: new insights into the mechanisms of insectâplant interactions and evolution
International audienceThe availability of model microbial pathogens and plants has been key to characterizing resistance and virulence pathways and to shedding light on the mechanisms of hostâparasite interactions and co-evolution (e.g. Allen et al. 2004, Science 306, 1957â1960; Bergelson et al. 2001, Science 292, 2281â2285). However, the absence of genetically tractable arthropod parasites of model plants has impeded so far our ability to gain better insights into the mechanisms, evolution and ecological consequences of plantâherbivore interactions. In this issue of Molecular Ecology, Whiteman et al. (2011) highlight fascinating features of a drosophilid fly, Scaptomyza flava, that feeds on the model plant Arabidopsis thaliana. They explore the potential of this system for studying insectâplant interactions with a clever mix of phenotypic and genetic experiments providing a comprehensive and persuasive argument for the validity of this model system. This study sets the ground for key developments in the unravelling of mechanisms involved in (i) plantâinsect interactions and co-evolution, and (ii) transition to herbivory in arthropods and evolution of endophagous lifestyles
Evolution and Origin of Polydnavirus Virulence Genes. In Symbionts and Pathogens
International audiencePolydnaviruses (PDVs) have a unique life-cycle, comprised of a mutualistic lifestyle with their associated parasitoid wasps and a parasitic interaction with the lepidopteran wasp hosts. They are present as proviruses in the parasitoid wasps that harbor them. The female wasps produce particles that contain circular double-stranded DNA versions of the viruses that are injected into the wasps' lepidopteran hosts. This 'injected circular form' is replication deficient but is absolutely essential for the physiological regulation of caterpillars that leads to parasitoid survival. PDVs are divided into two genera, bracoviruses (BVs) and ichnoviruses (IVs) associated with tens of thousands of endoparasitoid braconid and ichneumonid wasps, respectively, belonging to the Ichneumonoidea superfamily. The absence of PDVs in basal lineages of Ichneumonoidea strongly suggests that the association of BVs with braconids and IVs with ichneumonids arose independently. In ichneumonids, PDVs have been identified in the Campopleginae and Banchinae subfamily. The unique genomic features of the first banchine virus examined to date also suggest they could have an origin distinct from those of IVs and BVs (Lapointe et al., 2007). The absence of genes involved in virus production in the injected circular form is likely to be a signature of the reductive evolution that these PDVs have been subjected to, due to their reliance on wasps for transmission and the absence of replication in host larvae. In this chapter, we will focus on the PDV circular genomes that are injected into the lepidopteran hosts and highlight how selection pressures are likely to have modeled their content, organization, gene function, and efficiency. These PDV genomes are atypical for viruses in the sense that they harbor numerous genes, many of whic
Génome et facteurs de virulence d'un polydnavirus d'hyménoptÚre parasitoïde
The hymenoptera Cotesia congregata lays its eggs into its host, a caterpillar of the lepidoptera Manduca sexta and introduces bracovirus (CcBV) particles. The proteins encoded by viral genes expressed in the parasitized host play an essential role for succesful parasitism, leading to modifications of host physiology such as alteration of immunity and prewandering developmental arrest. The introduction of this thesis summarizes up-to-date knowledge about insect immunity and bracoviral genes potentially involved in host physiology control. Sequencing and genome analyses demonstrated that the CcBV genome is composed of 30 double-stranded DNA circles coding for 9 multigenic families comprising protein tyrosine phosphatases, cystatins and ankyrin motif containing proteins. The characterisation of the viral genes expressed in the host is a key step toward further identification of the role of each protein in host physiology alteration. Field inversion gel electrophoresis (FIGE) allowed to physically localize PTP genes on the viral genome. Their expression was analysed on different host tissues by a multiplex RT PCR method. Next, biochemical activity tests of 2 PTPs were performed. Globally, genes of the described families are expressed in the parasitized host and some proteins have the biochemical function predicted by their conserved domains, suggesting these proteins play a role in the host physiological modifications induces by parasitism.L'hymĂ©noptĂšre Cotesia congregata pond dans un hĂŽte, la chenille du lĂ©pidoptĂšre Manduca sexta et introduit des particules virales de bracovirus (CcBV). Les protĂ©ines codĂ©es par les gĂšnes viraux exprimĂ©es dans l'hĂŽte parasitĂ© jouent un rĂŽle indispensable Ă la rĂ©ussite parasitaire, entraĂźnant des modifications de la physiologie de l'hĂŽte, notamment une altĂ©ration de l'immunitĂ© et un arrĂȘt du dĂ©veloppement au stade prĂ©-pupal. Une synthĂšse des connaissances actuelles sur l'immunitĂ© des insectes et les gĂšnes de bracovirus potentiellement impliquĂ©s dans le contro le de la physiologie des hĂŽtes est prĂ©sentĂ©e en introduction. Le sĂ©quençage et l'analyse du gĂ©nome de CcBV ont montrĂ© que ce gĂ©nome est composĂ© de 30 cercles d'ADN double-brin porteurs de 9 familles multigĂ©niques : la famille des protĂ©ines tyrosines phosphatases (PTP), des cystatines, des protĂ©ines ankyrines... La caractĂ©risation des gĂšnes viraux exprimĂ©s dans l'hĂŽte est une Ă©tape indispensable vers l'identification du rĂŽle individuel de chaque protĂ©ine dans le contrĂŽle de la physiologie de l'hĂŽte. La technique d'Ă©lectrophorĂšse en champs inversĂ©s (FIGE) a permis la localisation physique sur l'ensemble du gĂ©nome viral des gĂšnes de PTP. Leur expression a Ă©tĂ© analysĂ©e dans diffĂ©rents tissus de l'hĂŽte parasitĂ© par une mĂ©thode de PCR multiplex. Puis des tests d'activitĂ© biochimique de 2 PTP ont Ă©tĂ© menĂ©s. Les gĂšnes des familles dĂ©crites sont exprimĂ©s dans l'hĂŽte parasitĂ© et certaines protĂ©ines possĂšdent la fonction biochimique prĂ©dite par les domaines conservĂ©s, suggĂ©rant que ces protĂ©ines jouent un rĂŽle dans la modification de la physiologie de l'hĂŽte induite par le parasitisme.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF
Insect-induced effects on plants and possible effectors used by galling and leaf-mining insects to manipulate their host-plant
International audienc
When parasitic wasps hijacked viruses: genomic and functional evolution of polydnaviruses
International audienceThe Polydnaviridae (PDV), including the Bracovirus (BV) and Ichnovirus genera, originated from the integration of unrelated viruses in the genomes of two parasitoid wasp lineages, in a remarkable example of convergent evolution. Functionally active PDVs represent the most compelling evolutionary success among endogenous viral elements (EVEs). BV evolved from the domestication by braconid wasps of a nudivirus 100 Ma. The nudivirus genome has become an EVE involved in BV particle production but is not encapsidated. Instead, BV genomes have co-opted virulence genes, used by the wasps to control the immunity and development of their hosts. Gene transfers and duplications have shaped BV genomes, now encoding hundreds of genes. Phylogenomic studies suggest that BVs contribute largely to wasp diversification and adaptation to their hosts. A genome evolution model explains how multidirectional wasp adaptation to different host species could have fostered PDV genome extension. Integrative studies linking ecological data on the wasp to genomic analyses should provide new insights into the adaptive role of particular BV genes. Forthcoming genomic advances should also indicate if the associations between endoparasitoid wasps and symbiotic viruses evolved because of their particularly intimate interactions with their hosts, or if similar domesticated EVEs could be uncovered in other parasites
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