Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
Symbioses with the dinoflagellate Symbiodinium are widespread among marine invertebrates and protists, especially in nutritionally demanding habitats, such as tropical coral reefs, where they play a major role in ecosystem survival. Moreover, apart from corals and sea anemones, many of the Symbiodinium species and clades involved in these partnerships remain to be characterized. This study provides new insights into nudibranch and sponge associations with Symbiodinium by sequencing regions of the Symbiodinium 28S rDNA and the host mitochondrial COI oxidase. Specimens were sampled between 2011 and 2013 from locations around the islands of Moorea and Tahiti, French Polynesia. Our results revealed that some of the sponges and nudibranchs harbored typical Symbiodinium from clade B or C while others harbored new, undescribed Symbiodinium-like dinoflagellates. A detailed analysis of the different life stages of the nudibranch Phestilla lugubris and of its specific coral prey, Porites rus, suggests a prey-predator horizontal transfer of the symbiont and its vertical inheritance from the parent to the eggs.
Les symbioses à zooxanthelles, dinoflagellés du genre Symbiodinium, sont largement répandues chez les invertébrés marins et les protozoaires, notamment dans les eaux oligotrophes, où ils jouent un rôle important dans la survie des récifs coralliens. De plus, excepté chez les coraux et les anémones, les différentes espèces et clades de Symbiodinium impliqués dans ces associations restent à être caractérisés. Notre étude, grâce à l’utilisation des marqueurs génétiques 28S ADNr des Symbiodinium et la sous-unité 1 de la cytochrome oxydase mitochondriale (COI) de l’hôte, procure de nouvelles données quant aux associations des éponges et des nudibranches avec les Symbiodinium. L’échantillonnage a eu lieu autour de Moorea et de Tahiti (Polynésie française), entre 2011 et 2013. Nos résultats révèlent que certaines espèces d’éponges et de nudibranches possèdent les clades B et C communément retrouvés, chez les coraux notamment, alors que d’autres présentent de nouveaux dinoflagellés « Symbiodinium-like ». Une analyses détaillée des Symbiodinium à différents stades du cycle de vie du nudibranche corallivore Phestilla lugubris et de son corail hôte Porites rus suggèrent l’existence d’un transfert horizontal de Symbiodinium proie–prédateur et un transfert vertical du parent P. lugubris à ses œufs.
ISSN: 1631-0691

hal-01145518
https://hal.archives-ouvertes.fr/hal-01145518
DOI : 10.1016/j.crvi.2015.01.005

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The actin cytoskeleton is a dynamic structure that provides an interactive platform for organelles and cellular components. It also serves as track for membranes and vesicles that move via myosin. The actin cytoskeleton of Symbiodinium is a well-organized reticular structure suggestive of multiple membrane interactions, very likely including those of the chloroplast. The Symbiodinium chloroplast membrane network is, in turn, a highly organized structure, suggestive of being under the control of an organizing network. We visualized the chloroplast membranes of cultured Symbiodinium sp. under various light conditions and observed changes dependent on illumination intensity. Since we suspected interaction between these two organelles, and we knew that the Symbiodinium actin cytoskeleton collapses upon treatment with either latrunculin B, an actin microfilament-disrupting agent, or butanedione monoxime, a myosin function inhibitor, we tested the Symbiodinium sp. oxygen evolution in their presence. Upon latrunculin B addition, the oxygen production decreased compared to non-treated cells; however, this was not observed after a 24 h latrunculin treatment. On the contrary, butanedione monoxime treatment caused a non-recoverable dysfunction of the chloroplast causing a severe loss in oxygen production even after long-term exposure. Using electron microscopy, we observed an alteration of the Symbiodinium sp. chloroplast distribution after latrunculin B treatment, with respect to untreated cells. Furthermore, a thorough disorganization of the chloroplast grana was observed after butanedione monoxime treatment. These data suggest that an actomyosin system would be important for chloroplast organization and distribution, and critical for normal photosynthetic function of Symbiodinium sp.
ISSN: 0166-8595

hal-01546164
https://hal.archives-ouvertes.fr/hal-01546164
DOI : 10.1007/s11120-015-0142-9

Éditeur(s) : HAL CCSD Oldendorf/Luhe
Résumé : International audience
Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure (pCO(2)) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO(2) on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO(2), i.e. sampling in situ natural CO2 vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO(2) had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO(2) induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO(2), we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO3- to a CO2 user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.
ISSN: 0171-8630

hal-01546163
https://hal.archives-ouvertes.fr/hal-01546163
DOI : 10.3354/meps11916

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
High sea surface temperature accompanied by high levels of solar irradiance is responsible for the disruption of the symbiosis between cnidarians and their symbiotic dinoflagellates from the genus Symbiodinium. This phenomenon, known as coral bleaching, is one of the major threats affecting coral reefs around the world. Because an important molecular trigger to bleaching appears related to the production of reactive oxygen species (ROS), it is critical to understand the function of the antioxidant network of Symbiodinium species. In this study we investigated the response of two Symbiodinium species, from contrasting environments, to a chemically induced oxidative stress. ROS produced during this oxidative burst reduced photosynthesis by 30 to 50% and significantly decreased the activity of superoxide dismutase. Lipid peroxidation levels and carotenoid concentrations, especially diatoxanthin, confirm that these molecules act as antioxidants and contribute to the stabilization of membrane lipids. The comparative analysis between the two Symbiodinium species allowed us to highlight that Symbiodinium sp. clade A temperate was more tolerant to oxidative stress than the tropical S. kawagutii clade F. These differences are very likely a consequence of adaptation to their natural environment, with the temperate species experiencing conditions of temperature and irradiance much more variable and extreme.
ISSN: 0140-7791

hal-01546161
https://hal.archives-ouvertes.fr/hal-01546161
DOI : 10.1111/pce.12825

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
The aim of this chapter is to provide a general overview of the main ecological aspects of Anthozoan-Symbiodinium mutualisms in the Mediterranean Sea. There are reports of at least twelve species of symbiotic anthozans in the basin. These anthozoans establish symbiotic relations with Symbiodinium Temperate A and B2 (Symbiodinium psygmophilum), corresponding to the only two species of Symbiodinium described in the region. A synthesis of the trophic and biochemical aspects of the interaction between Symbiodinum and their cnidarian hosts is given to contribute to the understanding of the mechanisms that maintain this special association. Finally, current knowledge about the ecological importance of this interaction in engineering species is examined. This review is framed to highlight the ecological importance of this symbiotic relationship in ecosystem construction and maintenance on an enclosed, temperate marine basin.
The Cnidaria, Past, Present and Future

ISBN : 978-3-319-31303-0
hal-01546929
http://hal.upmc.fr/hal-01546929
DOI : 10.1007/978-3-319-31305-4_24

Éditeur(s) : HAL CCSD PeerJ
Résumé : International audience
The adaptative bleaching hypothesis (ABH) states that, depending on the symbiotic flexibility of coral hosts (i.e., the ability of corals to ''switch'' or ''shuffle'' their algal symbionts), coral bleaching can lead to a change in the composition of their associated Symbiodinium community and, thus, contribute to the coral's overall survival. In order to determine the flexibility of corals, molecular tools are required to provide accurate species delineations and to detect low levels of coral-associated Symbiodinium. Here, we used highly sensitive quantitative (real-time) PCR (qPCR) technology to analyse five common coral species from Moorea (French Polynesia), previously screened using only traditional molecular methods, to assess the presence of low-abundance (background) Symbiodinium spp. Similar to other studies, each coral species exhibited a strong specificity to a particular clade, irrespective of the environment. In addition, however, each of the five species harboured at least one additional Symbiodinium clade, among clades A–D, at background levels. Unexpectedly, and for the first time in French Polynesia, clade B was detected as a coral symbiont. These results increase the number of known coral-Symbiodinium associations from corals found in French Polynesia, and likely indicate an underestimation of the ability of the corals in this region to associate with and/or ''shuffle'' different Symbiodinium clades. Altogether our data suggest that corals from French Polynesia may favor a trade-off between optimizing symbioses with a specific Symbiodinium clade(s), maintaining associations with particular background clades that may play a role in the ability of corals to respond to environmental change. How to cite this article Rouzé et al. (2017), An updated assessment of Symbiodinium spp. that associate with common scleractinian corals from Moorea (French Polynesia) reveals high diversity among background symbionts and a novel finding of clade B.
ISSN: 2167-8359

Droits : info:eu-repo/semantics/OpenAccess
hal-01430294
https://hal-sde.archives-ouvertes.fr/hal-01430294
https://hal-sde.archives-ouvertes.fr/hal-01430294/document
https://hal-sde.archives-ouvertes.fr/hal-01430294/file/Rouze-2017-PeerJ-Updated.pdf
DOI : 10.7717/peerj.2856

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
This study provides a baseline describing natural small scale variability of Symbiodinium density in the sentinel coral Acropora globiceps during the summer, under non-bleaching conditions. Spatial scales investigated range from the colony scale (1-10 cm, i.e. among branches of the same colony) to the reef scale (1-10 km, i.e. among stations distributed over several locations and depths), at Moorea Island, French Polynesia. The coral-Symbiodinium symbiosis is a key process in scleractinian coral physiology, and Symbiodinium density provides an easy-to-measure and inexpensive biomarker of this symbiosis health. Spatial variability of three major environmental factors: light intensity, sedimentation and water motion was also assessed to evaluate their potential link with Symbiodinium density. Density of Symbiodinium did not significantly differ within colonies or among colonies within a station. However, a marked depth gradient was observed, showing increasing density with increasing depth and decreasing light intensity. These observations provide an interesting reference for forthcoming comparisons with disturbed conditions, such as bleaching events.
ISSN: 0025-3154

hal-00905942
https://hal.archives-ouvertes.fr/hal-00905942
https://hal.archives-ouvertes.fr/hal-00905942/document
https://hal.archives-ouvertes.fr/hal-00905942/file/Ladriereetal2014.pdf
DOI : 10.1017/S0025315413001252

Éditeur(s) : HAL CCSD Wiley Open Access
Résumé : International audience
Coral disease outbreaks have increased over the last three decades, but their causal agents remain mostly unclear (e.g., bacteria, viruses, fungi, protists). This study details a 14-month-long survey of coral colonies in which observations of the development of disease was observed in nearly half of the sampled colonies. A bimonthly qPCR method was used to quantitatively and qualitatively evaluate Symbiodinium assemblages of tagged colonies, and to detect the presence of Vibrio spp. Firstly, our data showed that predisposition to disease development in general, and, more specifically, infection by Vibrio spp. in Acropora cytherea depended on which clades of Symbiodinium were harbored. In both cases, harboring clade D rather than A was beneficial to the coral host. Secondly, the detection of Vibrio spp. in only colonies that developed disease strongly suggests opportunistic traits of the bacteria. Finally, even if sporadic cases of switching and probably shuffling were observed, this long-term survey does not suggest specific-clade recruitment in response to stressors. Altogether, our results demonstrate that the fitness of the coral holobiont depends on its initial consortium of Symbiodinium, which is distinct among colonies, rather than a temporary adaptation achieved through acquiring different Symbiodinium clades.
ISSN: 2045-7758

hal-01346931
https://hal-uvsq.archives-ouvertes.fr/hal-01346931
https://hal-uvsq.archives-ouvertes.fr/hal-01346931/document
https://hal-uvsq.archives-ouvertes.fr/hal-01346931/file/2016%20Rouze%20EcolEvol.pdf
DOI : 10.1002/ece3.1895

Éditeur(s) : HAL CCSD Wiley Open Access
Résumé : International audience
Coral disease outbreaks have increased over the last three decades, but their causal agents remain mostly unclear (e.g., bacteria, viruses, fungi, protists). This study details a 14-month-long survey of coral colonies in which observations of the development of disease was observed in nearly half of the sampled colonies. A bimonthly qPCR method was used to quantitatively and qualitatively evaluate Symbiodinium assemblages of tagged colonies, and to detect the presence of Vibrio spp. Firstly, our data showed that predisposition to disease development in general, and, more specifically, infection by Vibrio spp. in Acropora cytherea depended on which clades of Symbiodinium were harbored. In both cases, harboring clade D rather than A was beneficial to the coral host. Secondly, the detection of Vibrio spp. in only colonies that developed disease strongly suggests opportunistic traits of the bacteria. Finally, even if sporadic cases of switching and probably shuffling were observed, this long-term survey does not suggest specific-clade recruitment in response to stressors. Altogether, our results demonstrate that the fitness of the coral holobiont depends on its initial consortium of Symbiodinium, which is distinct among colonies, rather than a temporary adaptation achieved through acquiring different Symbiodinium clades.
ISSN: 2045-7758

hal-01270779
https://hal-univ-perp.archives-ouvertes.fr/hal-01270779
https://hal-univ-perp.archives-ouvertes.fr/hal-01270779/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01270779/file/41080.pdf
DOI : 10.1002/ece3.1895

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cnidarian-dinoflagellate symbiosis mainly relies on nutrient recycling, thus providing both partners with a competitive advantage in nutrient-poor waters. Essential processes related to lipid metabolism can be influenced by various factors, including hyperthermal stress. This can affect the lipid content and distribution in both partners, while contributing to symbiosis disruption and bleaching. In order to gain further insight into the role and distribution of lipids in the cnidarian metabolism, we investigated the lipid composition of the sea anemone Anemonia viridis and its photosynthetic dinoflagellate endosymbionts (Symbiodinium). We compared the lipid content and fatty acid profiles of the host cellular layers, non-symbiotic epidermal and symbiont-containing gastrodermal cells, and those of Symbiodinium, in a mass spectrometry-based assessment. Lipids were more concentrated in Symbiodinium cells, and the lipid class distribution was dominated by polar lipids in all tissues. The fatty acid distribution between host cell layers and Symbiodinium cells suggested potential lipid transfers between the partners. The lipid composition and distribution was modified during short-term hyperthermal stress, mainly in Symbiodinium cells and gastrodermis. Exposure to elevated temperature rapidly caused a decrease in polar lipid C18 unsaturated fatty acids and a strong and rapid decrease in the abundance of polar lipid fatty acids relative to sterols. These lipid indicators could therefore be used as sensitive biomarkers to assess the physiology of symbiotic cnidarians, especially the effect of thermal stress at the onset of cnidarian bleaching. Overall, the findings of this study provide some insight on key lipids that may regulate maintenance of the symbiotic interaction.
ISSN: 1095-6433

hal-01546160
https://hal.archives-ouvertes.fr/hal-01546160
DOI : 10.1016/j.cbpa.2015.10.017

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cnidarians living in symbiosis with photosynthetic dinoflagellates (commonly named zooxanthellae) are exposed to high concentrations of reactive oxygen species (ROS) upon illumination. To quench ROS production, both the cnidarian host and zooxanthellae express a full suite of antioxidant enzymes. Studying antioxidative balance is therefore crucial to understanding how symbiotic cnidarians cope with ROS production. We characterized glutathione peroxidases (GPx) in the symbiotic cnidarian Anemonia viridis by analysis of their isoform diversity, their activity distribution in the three cellular compartments (ectoderm, endoderm and zooxanthellae) and their involvement in the response to thermal stress. We identified a GPx repertoire through a phylogenetic analysis showing 7 GPx transcripts belonging to the A. viridis host and 4 GPx transcripts strongly related to Symbiodinium sp. The biochemical approach, used for the first time with a cnidarian species, allowed the identification of GPx activity in the three cellular compartments and in the animal mitochondrial fraction, and revealed a high GPx electrophoretic diversity. The symbiotic lifestyle of zooxanthellae requires more GPx activity and diversity than that of free-living species. Heat stress induced no modification of GPx activities. We highlight a high GPx diversity in A. viridis tissues by genomic and biochemical approaches. GPx activities represent an overall constitutive enzymatic pattern inherent to symbiotic lifestyle adaptation. This work allows the characterization of the GPx family in a symbiotic cnidarian and establishes a foundation for future studies of GPx in symbiotic cnidarians.
ISSN: 0300-9084

hal-01404424
http://hal.upmc.fr/hal-01404424
http://hal.upmc.fr/hal-01404424/document
http://hal.upmc.fr/hal-01404424/file/Pey_Characterization_of.pdf
DOI : 10.1016/j.biochi.2016.10.016

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Cnidarian-dinoflagellate symbiosis disruption and subsequent bleaching are major concerns, especially regarding their ecological consequences on coral reefs and temperate coralligenous communities. Cnidarian bleaching is caused by a variety of environmental stressors, such as elevated seawater temperature associated with global climate change, and by pollutants, such as herbicides and metals. Several cellular events have been described to explain symbiosis dysfunction and bleaching. Excess or damaged Symbiodinium symbionts are removed through a variety of mechanisms, including exocytosis, apoptosis, necrosis and autophagy. However, few studies have compared in the same species the relative involvement of these mechanisms, according to the stress inducing the bleaching. In this study, we used two different treatments —temperature and menthol— to induce bleaching in the sea anemone Anemonia viridis. By monitoring the ultrastructural tissue modifications, in control specimens we observed a basal rate of in situ symbiont digestion —or symbiophagy— induced by starvation. Symbiophagy was strongly induced in menthol-treated specimens and was the main cellular process of bleaching, whereas apoptosis and necrosis predominated in hyperthermal-induced bleaching. These results suggested a host effect through autophagy in menthol-treated specimens. These observations also suggested that symbiont removal may result from reengagement of the phagosomal maturation process in the host. These overall data demonstrate that several Symbiodinium cell removal mechanisms coexist and that stressors can activate one or more of these pathways, depending on the stress type, intensity or duration.
ISSN: 0334-5114

hal-01546908
http://hal.upmc.fr/hal-01546908
DOI : 10.1007/s13199-016-0406-y

Éditeur(s) : HAL CCSD
Résumé : The trophic endosymbiosis interaction between a cnidarian host and its photosynthetic dinoflagellatessymbionts form the basis of coral reef ecosystems. Cnidarians host their symbionts in gastrodermis cells, in a phagocytosis-derived vacuole. Establishment and maintenance of the symbiotic interaction depend on an intimate molecular communication between the two partners. However, environmental and/or anthropogenic disturbances can lead to the breakdown of the symbiotic association, which is responsible for the worldwide decline of coral reefs. The main objectives of my research project are to improve the knowledge regarding symbiosis maintenance and disruption mechanisms, but also to define the molecular key players involved at the symbiotic interface in the sea anemone, Anemonia viridis. First, we have described the cellular mechanisms involved in the different types of symbiosis breackdown. Meanwhile, the characterization of npc1 and npc2 genes (involved in endosomal sterol transport), showed a duplication and a sub-functionalization of the npc2d gene. Both NPC1 and NPC2 proteins are expressed around symbionts. We therefore suggest that the duplicated protein NPC2-d is a biomarker of symbiosis health and that NPC1 protein is a marker of the perisymbiotic membrane. We then developed a protocol to characterize the proteome of the symbiotic interface between the two symbiotic partners. The newly-identified symbiotic key players will increase the general knowledge on the symbiotic interaction and its regulation during both stable and bleaching conditions.
L’endosymbiose trophique établie entre un hôte Cnidaire et ses symbiotes Dinoflagellés photosynthétiques est à l’origine du succès évolutif des écosystèmes coralliens. Les symbiotes sont internalisés par un mécanisme de phagocytose et maintenus dans les cellules du gastroderme de l'hôte. La symbiose est régie par un dialogue moléculaire intime entre les deux partenaires, interrompu lors de perturbations environnementales ou anthropiques, responsables du déclin mondial des récifs coralliens. Les objectifs de mon projet de recherche sont de définir les acteurs moléculaires localisés à l’interface symbiotique chez l’anémone de mer, Anemonia viridis. Premièrement, nous avons étudié les mécanismes cellulaires impliqués dans différents types de rupture de la symbiose et mis en évidence des phénomènes d’apoptose, nécrose et symbiophagie. Parallèlement, nous avons caractérisé chez l’anémone les gènes npc1 et npc2, impliqués chez les vertébrés dans le transport endosomal de stérols, et dont l’expression est modulée par l’état symbiotique. Nous avons pu montrer que le gène npc2d est issus d’une duplication et vraisemblablement d’une sub-fonctionnalisation et que les protéines NPC1 et NPC2 sont exprimées au voisinage des symbiotes. Nous proposons donc que la protéine NPC2-d soit utilisée comme marqueur de l’état de santé des Anthozoaires symbiotiques et que la protéine NPC1 soit un marqueur de la membrane périsymbiotique. Nous avons également développé un protocole afin d’identifier les protéines associées à l’interface symbiotique entre les deux partenaires. A terme, les cibles identifiées permettront une meilleure compréhension des mécanismes qui régulent la relation symbiotique.
https://tel.archives-ouvertes.fr/tel-01673491

NNT : 2015NICE4105
tel-01673491
https://tel.archives-ouvertes.fr/tel-01673491
https://tel.archives-ouvertes.fr/tel-01673491/document
https://tel.archives-ouvertes.fr/tel-01673491/file/2015NICE4105.pdf

Éditeur(s) : HAL CCSD
Résumé : The ecological success of cnidarian-dinoflagellate symbiosis mainly relies on nutrient recycling. Environmental changes, such as global warming or pollution, often result to symbiosis breakdown, also called cnidarian bleaching. The understanding of mechanisms regulating the symbiosis establishment, maintenance and breakdown is essential to prevent massive bleaching phenomena. In this respect, my PhD project focused on the characterization of chemical mediators expressed in the sea anemone Anemonia viridis, their localization and their modulation by stress conditions. A comparative study was first conducted to characterize the chemical mediators and analyze their distribution within the symbiotic sea anemone. We described a great abundance and diversity of lipids in A. viridis tissues. From these results, we proposed possible transfers of FAs between the symbiotic partners. A thermal stress and a chemical stress have also been applied in laboratory-controlled conditions in order to induce symbiosis breakdown and bleaching of the sea anemones, in order to correlate A. viridis metabolome to its symbiotic status. A mapping of these metabolites has been performed by MALDI-MSI of tentacle cross-sections, as well as their evolution following stress. Some betaine lipids have thus been proposed as short-term indicators of stress. A. viridis stress response has also been evaluated with a lipidomic approach, and allowed to identify 3 lipid indicators of early stress response based on membrane fluidity markers. Overall, this study provides insight on key chemical mediators that may regulate the symbiosis maintenance, and may contribute to the symbiosis breakdown.
Le succès évolutif des Cnidaires symbiotiques réside en grande partie dans leurs échanges trophiques établis avec les Dinoflagellés du genre Symbiodinium. Cependant, le réchauffement climatique global ainsi que les pollutions ont un impact fort sur les écosystèmes coralliens, notamment en conduisant à la rupture de la symbiose, phénomène appelé blanchissement. La compréhension des mécanismes qui régissent l’établissement, le maintien et la rupture de la symbiose est essentielle à la prévention des épisodes de blanchissement massif. Dans ce contexte, les objectifs de mon projet de thèse sont de caractériser les médiateurs chimiques de l’anémone de mer Anemonia viridis, de les localiser, et d’analyser leur réponse face à un stress. Parmi les composés caractérisés, les lipides et les bétaïnes sont les plus abondants et présentent une grande diversité. Certains sont transférés des symbiotes vers l’hôte. Des anémones de mer ont ensuite été traitées en laboratoire afin de provoquer la rupture de la symbiose et le blanchissement des individus. Une étude cinétique a été menée par une approche globale comparative identique à celle réalisée sur l’anémone symbiotique. Par ailleurs, une cartographie de l’évolution de composés clé a été réalisée par MALDI-MSI. La réponse au stress a été évaluée et a permis d’identifier des lipides de bétaïne et trois indicateurs lipidiques comme marqueurs de réponse précoce au stress. L’ensemble de ces résultats apporte de nouveaux éléments de réponse concernant le rôle des médiateurs chimiques clés dans le maintien de la symbiose, ainsi que leur influence sur sa rupture.
https://tel.archives-ouvertes.fr/tel-01310668

NNT : 2015NICE4108
tel-01310668
https://tel.archives-ouvertes.fr/tel-01310668
https://tel.archives-ouvertes.fr/tel-01310668/document
https://tel.archives-ouvertes.fr/tel-01310668/file/2015NICE4108.pdf

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The symbiotic interaction between cnidarians, such as corals and sea anemones, and the unicellular algae Symbiodinium is regulated by yet poorly understood cellular mechanisms, despite the ecological importance of coral reefs. These mechanisms, including host-symbiont recognition and metabolic exchange, control symbiosis stability under normal conditions, but also lead to symbiosis breakdown (bleaching) during stress. This study describes the repertoire of the sterol-trafficking proteins Niemann-Pick type C (NPC1 and NPC2) in the symbiotic sea anemone Anemonia viridis. We found one NPC1 gene in contrast to the two genes (NPC1 and NPC1L1) present in vertebrate genomes. While only one NPC2 gene is present in many metazoans, this gene has been duplicated in cnidarians, and we detected four NPC2 genes in A. viridis. However, only one gene (AvNPC2-d) was upregulated in symbiotic relative to aposymbiotic sea anemones and displayed higher expression in the gastrodermis (symbiont-containing tissue) than in the epidermis. We performed immunolabelling experiments on tentacle cross sections and demonstrated that the AvNPC2-d protein was closely associated with symbiosomes. In addition, AvNPC1 and AvNPC2-d gene expression was strongly downregulated during stress. These data suggest that AvNPC2-d is involved in both the stability and dysfunction of cnidarian-dinoflagellate symbioses.
ISSN: 0962-1083

hal-01546166
https://hal.archives-ouvertes.fr/hal-01546166
DOI : 10.1111/mec.12876