Endosymbiosis drives transcriptomic adjustements and genomic adapatations in cnidarians

To decipher inter-partner signaling within the cnidarian-dinoflagellate endosymbiosis, we developed genomic resources (cDNA library and microarrays) for the symbiotic sea anemone Anemonia viridis. Differential gene expression was quantified during thermal stress, with and without UV radiation, between symbiotic vs aposymbiotic specimens and gastroderm vs epidermis tissues. During stress time-course experiments, each stress showed a specific gene expression profile with very little overlap. We show that the major response to thermal stress is rapid (24 hours) but returns to the baseline levels after 2 days. UVR alone has little effect but potentiates thermal stress, as expression of a second set of genes becomes differentially expressed at day 5. Analysis of genes differentially expressed between symbiotic vs bleached and symbiotic vs stressed specimens defined a restricted subset of genes (Kern). Tissue specific expression mapping of Kern genes showed that many were specifically enhanced in the symbiotic cells (gastroderm). Altogether, these data define the Kern genes as major molecular components of the symbiotic interaction. Functional annotations highlighted several pathways including collagen fibrillogenesis, vesicular trafficking, lipid metabolism, calcium signaling, inorganic carbon transfer and cell death, that were modified by stress. Phylogenomic investigations of several Kern genes (calumenin, NPC2, SYM32, dermatopontin, and Rhbg) demonstrate that these issued from cnidarian specific duplication events, with the Kern member being preferentially expressed in the gastroderm and specifically responding to stress. Such host specific genes subfunctionalizations suggest both genomic and transcriptomic adaptations driven by the physiological constraints of endosymbiosis

Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation

Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance

Stable Photosymbiotic Relationship under CO2-Induced Acidification in the Acoel Worm Symsagittifera Roscoffensis

As a consequence of anthropogenic CO2 emissions, oceans are becoming more acidic, a phenomenon known as ocean acidification. Many marine species predicted to be sensitive to this stressor are photosymbiotic, including corals and foraminifera. However, the direct impact of ocean acidification on the relationship between the photosynthetic and nonphotosynthetic organism remains unclear and is complicated by other physiological processes known to be sensitive to ocean acidification (e.g. calcification and feeding). We have studied the impact of extreme pH decrease/pCO2 increase on the complete life cycle of the photosymbiotic, non-calcifying and pure autotrophic acoel worm, Symsagittifera roscoffensis. Our results show that this species is resistant to high pCO2 with no negative or even positive effects on fitness (survival, growth, fertility) and/or photosymbiotic relationship till pCO2 up to 54 K µatm. Some sub-lethal bleaching is only observed at pCO2 up to 270 K µatm when seawater is saturated by CO2. This indicates that photosymbiosis can be resistant to high pCO2. If such a finding would be confirmed in other photosymbiotic species, we could then hypothesize that negative impact of high pCO2 observed on other photosymbiotic species such as corals and foraminifera could occur through indirect impacts at other levels (calcification, feeding)

Adaptations to Endosymbiosis in a Cnidarian-Dinoflagellate Association: Differential Gene Expression and Specific Gene Duplications

Trophic endosymbiosis between anthozoans and photosynthetic dinoflagellates forms the key foundation of reef ecosystems. Dysfunction and collapse of symbiosis lead to bleaching (symbiont expulsion), which is responsible for the severe worldwide decline of coral reefs. Molecular signals are central to the stability of this partnership and are therefore closely related to coral health. To decipher inter-partner signaling, we developed genomic resources (cDNA library and microarrays) from the symbiotic sea anemone Anemonia viridis. Here we describe differential expression between symbiotic (also called zooxanthellate anemones) or aposymbiotic (also called bleached) A. viridis specimens, using microarray hybridizations and qPCR experiments. We mapped, for the first time, transcript abundance separately in the epidermal cell layer and the gastrodermal cells that host photosynthetic symbionts. Transcriptomic profiles showed large inter-individual variability, indicating that aposymbiosis could be induced by different pathways. We defined a restricted subset of 39 common genes that are characteristic of the symbiotic or aposymbiotic states. We demonstrated that transcription of many genes belonging to this set is specifically enhanced in the symbiotic cells (gastroderm). A model is proposed where the aposymbiotic and therefore heterotrophic state triggers vesicular trafficking, whereas the symbiotic and therefore autotrophic state favors metabolic exchanges between host and symbiont. Several genetic pathways were investigated in more detail: i) a key vitamin K–dependant process involved in the dinoflagellate-cnidarian recognition; ii) two cnidarian tissue-specific carbonic anhydrases involved in the carbon transfer from the environment to the intracellular symbionts; iii) host collagen synthesis, mostly supported by the symbiotic tissue. Further, we identified specific gene duplications and showed that the cnidarian-specific isoform was also up-regulated both in the symbiotic state and in the gastroderm. Our results thus offer new insight into the inter-partner signaling required for the physiological mechanisms of the symbiosis that is crucial for coral health

Structural Insights into Viral Determinants of Nematode Mediated Grapevine fanleaf virus Transmission

Many animal and plant viruses rely on vectors for their transmission from host to host. Grapevine fanleaf virus (GFLV), a picorna-like virus from plants, is transmitted specifically by the ectoparasitic nematode Xiphinema index. The icosahedral capsid of GFLV, which consists of 60 identical coat protein subunits (CP), carries the determinants of this specificity. Here, we provide novel insight into GFLV transmission by nematodes through a comparative structural and functional analysis of two GFLV variants. We isolated a mutant GFLV strain (GFLV-TD) poorly transmissible by nematodes, and showed that the transmission defect is due to a glycine to aspartate mutation at position 297 (Gly297Asp) in the CP. We next determined the crystal structures of the wild-type GFLV strain F13 at 3.0 Å and of GFLV-TD at 2.7 Å resolution. The Gly297Asp mutation mapped to an exposed loop at the outer surface of the capsid and did not affect the conformation of the assembled capsid, nor of individual CP molecules. The loop is part of a positively charged pocket that includes a previously identified determinant of transmission. We propose that this pocket is a ligand-binding site with essential function in GFLV transmission by X. index. Our data suggest that perturbation of the electrostatic landscape of this pocket affects the interaction of the virion with specific receptors of the nematode's feeding apparatus, and thereby severely diminishes its transmission efficiency. These data provide a first structural insight into the interactions between a plant virus and a nematode vector

Approches physiologique et moléculaire de la calcification et de la "light-enhanced calcification" chez le corail Scléractiniaire Stylophora pistillata (Esper, 1797)

Les récifs coralliens, majoritairement édifiés par les coraux Scléractiniaires, constituent la plus importante construction biologique à l échelle mondiale. De nombreux coraux Scléractiniaires établissent une symbiose avec un Dinobionte photosynthétique. Cette symbiose est responsable, entre autres, d une stimulation de la calcification des coraux en présence de lumie re, phénomène décrit sous le terme de light-enhanced calcification (LEC). Malgré de nombreuses recherches, les mécanismes responsables de ce phénomène de LEC restent méconnus. Ma thèse a consisté en l étude de la calcification et du phénomène de LEC chez le corail Stylophora pistillata par une double approche physiologique (caractérisation du phénomène chez cette espèce, cycle journalier, temps de transition) et moléculaire (caractérisation moléculaire et localisation tissulaire d une anhydrase carbonique impliquée dans le processus de calcification, régulation transcriptionnelle entre les conditions "Jour" et "Nuit").Scleractinian corals are the main calcifying organisms of coral reefs. Most scleractinian corals establish a symbiotic relationship with phototrophic Dinoflagellates. This symbiosis is responsible for the stimulation of coral calcification by light, a phenomenon called light enhanced calcification (LEC). Despite numerous studies performed on this subject, the mechanisms linking photosynthesis of the symbionts to coral calcification remain largely unknown. The aim of the present work is to gain a better understanding of the calcification process and of the light-enhanced calcification phenomenon in the scleractinian coral Stylophora pistillata (Esper, 1797), using both physiological (characterization of the LEC phenomenon in S. pistillata, daily cycle, time transitions) and molecular approaches (molecular characterization and tissular localization of a carbonic anhydrase involved in the calcification process, transcriptional regulation between light and dark conditions).AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceMonacoFRM

Seawater carbonate chemistry, growth rate and hatching processes of Symsagittifera roscoffensis during experiments, 2012

As a consequence of anthropogenic CO2 emissions, oceans are becoming more acidic, a phenomenon known as ocean acidification. Many marine species predicted to be sensitive to this stressor are photosymbiotic, including corals and foraminifera. However, the direct impact of ocean acidification on the relationship between the photosynthetic and nonphotosynthetic organism remains unclear and is complicated by other physiological processes known to be sensitive to ocean acidification (e.g. calcification and feeding). We have studied the impact of extreme pH decrease/pCO2 increase on the complete life cycle of the photosymbiotic, non-calcifying and pure autotrophic acoel worm, Symsagittifera roscoffensis. Our results show that this species is resistant to high pCO2 with no negative or even positive effects on fitness (survival, growth, fertility) and/or photosymbiotic relationship till pCO2 up to 54 K µatm. Some sub-lethal bleaching is only observed at pCO2 up to 270 K µatm when seawater is saturated by CO2. This indicates that photosymbiosis can be resistant to high pCO2. If such a finding would be confirmed in other photosymbiotic species, we could then hypothesize that negative impact of high pCO2 observed on other photosymbiotic species such as corals and foraminifera could occur through indirect impacts at other levels (calcification, feeding)

Endosymbiosis drives transcriptomic adjustements and genomic adapatations in cnidarians

To decipher inter-partner signaling within the cnidarian-dinoflagellate endosymbiosis, we developed genomic resources (cDNA library and microarrays) for the symbiotic sea anemone Anemonia viridis. Differential gene expression was quantified during thermal stress, with and without UV radiation, between symbiotic vs aposymbiotic specimens and gastroderm vs epidermis tissues. During stress time-course experiments, each stress showed a specific gene expression profile with very little overlap. We show that the major response to thermal stress is rapid (24 hours) but returns to the baseline levels after 2 days. UVR alone has little effect but potentiates thermal stress, as expression of a second set of genes becomes differentially expressed at day 5. Analysis of genes differentially expressed between symbiotic vs bleached and symbiotic vs stressed specimens defined a restricted subset of genes (Kern). Tissue specific expression mapping of Kern genes showed that many were specifically enhanced in the symbiotic cells (gastroderm). Altogether, these data define the Kern genes as major molecular components of the symbiotic interaction. Functional annotations highlighted several pathways including collagen fibrillogenesis, vesicular trafficking, lipid metabolism, calcium signaling, inorganic carbon transfer and cell death, that were modified by stress. Phylogenomic investigations of several Kern genes (calumenin, NPC2, SYM32, dermatopontin, and Rhbg) demonstrate that these issued from cnidarian specific duplication events, with the Kern member being preferentially expressed in the gastroderm and specifically responding to stress. Such host specific genes subfunctionalizations suggest both genomic and transcriptomic adaptations driven by the physiological constraints of endosymbiosis

Summary of the impact of low <i>p</i>CO₂ (27063 µatm) on <i>S. roscoffensis</i> life cycle.

<p>Summary of the impact of low <i>p</i>CO₂ (27063 µatm) on <i>S. roscoffensis</i> life cycle.</p

Impact of a range of <i>p</i>CO₂ on: A. number of eggs produced per female; B. number of eggs per cocoon; C. number of cocoon produced per female (experiment 4).

<p>The number of eggs produced per female was 3 times higher in high compared to low <i>p</i>CO₂ (27 k vs 0.4 k µatm) and a significant logarithmic relationship was observed between the two parameters (F = 8.36, p<0.016; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029568#pone-0029568-g003" target="_blank">Figure 3A</a>). This was the consequence of an increased number of cocoon produced per female (significant logarithmic relationship, F = 7.79, p<0.02; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029568#pone-0029568-g003" target="_blank">Figure 3B</a>) with no effect on the number of eggs per cocoon (non significant logarithmic relationship, F = 0.43, p<0.53; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029568#pone-0029568-g003" target="_blank">Figure 3C</a>).</p