Analyse protéique de la matrice organique chez le genre Corallium, approche biochimique comparative et mécanistique

Les espèces du genre Corallium représentent un modèle d étude de la biominéralisation très intéressant : elles sont capables d élaborer deux structures squelettiques, un axe squelettique et des sclérites. Malgré des différences morphologiques et morphométriques importantes, ces structures sont toutes les deux composées d une fraction minérale de carbonate de calcium et d une fraction organique appelée matrice organique (MO). Cette MO interviendrait dans les différentes étapes du processus de biominéralisation. L étude comparée de cette MO représente donc une formidable opportunité pour déterminer les mécanismes de biominéralisation chez ces espèces. Par des approches comparatives intra- et inter-espèces, nous avons mis en évidence les caractéristiques biochimiques des protéines de MO chez différentes populations et espèces de Corallium. Nos résultats montrent à la fois des caractéristiques communes et des spécificités. Nous avons également établi que la caractérisation biochimique des protéines de MO est un critère d identification taxonomique chez ces espèces. De manière plus spécifique, la comparaison des protéines de MO des deux structures squelettiques chez C. rubrum a montré que certaines protéines présentent des caractéristiques biochimiques communes mais également des caractéristiques biochimiques différentes. Par la combinaison d approches biochimiques avec une approche transcriptomique, nous avons caractérisé la première protéine de MO chez l Octocoralliaire de Méditerranée, Corallium rubrum. Nos résultats montrent que le processus de formation du squelette chez les espèces du genre Corallium se fait par un mécanisme général commun aux différentes espècesCorallium genus species are very interesting biomineralization models: they build two skeletal structures with different size and form: an axial skeleton and sclerites. Despite their important morphological and morphometrical differences, both are composed of a mineral fraction of calcium carbonate and an organic fraction called organic matrix (OM). This OM is supposed to be involved in several biomineralization steps: nucleation, growth and orientation of crystals, final nano- and macro-architecture of biominerals. Comparative study of this OM thus represents a great opportunity to determine the fundamental mechanisms of biomineralization within these species. The aim of this PhD research project was to characterize OM proteins and inform on the skeletogenesis mechanisms among the Corallium genus. By comparative intra- and interspecies approaches, we have found OM proteic differences and similarities in different Corallium populations and species. Our results confirm a common growth mechanism and the possibility to use OM as a taxonomic criterion for these species. Moreover the comparison of OM proteins between the two skeletal structures in C. rubrum reveals proteins with identical biochemical characteristics and other with differences. Finally by the combinaison of these biochemical approaches with a transcriptomic one, we have characterized the first OM protein in the octocorallian species from the Mediterranean Sea, Corallium rubrumPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Lesion regeneration capacities in populations of the massive coral Porites lutea at Réunion Island: environmental correlates

The capacity of corals for repairing partial mortality is a fundamental determinant of reef resilience. This capacity was assessed in the major reef-building coral Porites lutea by monitoring the regeneration of artificially induced lesions of standard size (330 ± 50 mm2, 3 mm deep) in 4 shallow reef flat populations at Réunion Island, under different environmental conditions related to sites and seasons, during a period without positive temperature anomalies. An exponential decay model with an asymptote described the lesion regeneration through 14 experiments. In spite of fast initial lesion regeneration, limited capacity for repair in this massive coral was indicated, as only 18% of the inflicted lesions healed completely within 6 to 9 mo. Lesion regeneration was fastest and most complete in the cooling and cool seasons, and may be impaired during the warming and hot seasons. Both solar radiation and seawater temperature contributed to seasonal changes in regeneration capacity, although they had opposite effects. While high radiation during the warming season decreased lesion regeneration rate, potentially through reduction of the photosynthetic efficiency of zooxanthellae, high temperature boosted it but also increased the amount of lesion area that could not be regenerated. Study sites were characterised by different temperature and radiation regimes, but these parameters alone could not explain all site effects on lesion regeneration capacity. Additional factors, most probably chronic stress caused by inputs of organic matter and run-off from land, may further compromise the regeneration capacity of corals and the resilience of coral populations

Fast Growth May Impair Regeneration Capacity in the Branching Coral Acropora muricata

International audienceRegeneration of artificially induced lesions was monitored in nubbins of the branching coral Acropora muricata at two reef-flat sites representing contrasting environments at Réunion Island (21u079S, 55u329E). Growth of these injured nubbins was examined in parallel, and compared to controls. Biochemical compositions of the holobiont and the zooxanthellae density were determined at the onset of the experiment, and the photosynthetic efficiency (F v /F m) of zooxanthellae was monitored during the experiment. Acropora muricata rapidly regenerated small lesions, but regeneration rates significantly differed between sites. At the sheltered site characterized by high temperatures, temperature variations, and irradiance levels, regeneration took 192 days on average. At the exposed site, characterized by steadier temperatures and lower irradiation, nubbins demonstrated fast lesion repair (81 days), slower growth, lower zooxanthellae density, chlorophyll a concentration and lipid content than at the former site. A trade-off between growth and regeneration rates was evident here. High growth rates seem to impair regeneration capacity. We show that environmental conditions conducive to high zooxanthellae densities in corals are related to fast skeletal growth but also to reduced lesion regeneration rates. We hypothesize that a lowered regenerative capacity may be related to limited availability of energetic and cellular resources, consequences of coral holobionts operating at high levels of photosynthesis and associated growth

Environmental conditions.

<p>Daily average sea surface temperature (SST; ± SD, gray area) and cumulative daily solar radiation during the experimental period at (<b>a</b>) Planch’Alizé and (<b>b</b>) Kiosque.</p

Biochemical properties of nubbins of <i>Acropora muricata</i> at the onset of the lesion regeneration experiment.

*<p><i>p</i><0.05;</p>**<p><i>p</i><0.01;</p>***<p><i>p</i><0.001.</p

Calcification and lesion healing of <i>Acropora muricata</i>.

<p>Relationship between calcification rates and lesion healing for injured nubbins from Planch’Alizé and Kiosque.</p

Growth of <i>Acropora muricata</i>.

<p>The mean (± SD) relative increase in the projected surface area (‰ d⁻¹) of control and injured nubbins by site.</p

Molecular Cloning and Characterization of First Organic Matrix Protein from Sclerites of Red Coral, Corallium rubrum*

Background: Sclerites of alcyonarian species are biominerals formed of organic matrix molecules trapped inside a mineral inorganic fraction