Final Report Summary - CORALCLIMRESPONS (Revealing the response of the coral and its endosymbiotic algae to climate changes by molecular techniques)
The EU funded research project CORALCLIMRESPONSE is revealing the response of the coral and its endosymbiotic algae to different environmental stress by molecular techniques.
Tropical coral reefs shelter a high rate of marine biodiversity and provide a sizeable amount of ecological services. This ecosystem of interest face tremendous and pervasive challenges from human demography, sky rockets and inherent development pressures, as well as climate change and associated sea level rise. Prospects of coral reefs conservation, critically inevitable, will achieve through the growth of understanding their ecological mechanisms. The basis for the existence of tropical coral reefs is a mutualistic relationship between the coral polyp and its endosymbiotic dinoflagellates, the Symbiodinium sp.. Due to the consequence of global warming coral bleaching became one of the most important threats to coral reefs in the last decade. The higher temperatures and solar radiation disrupt photosynthesis in the coral’s symbiotic algae and result in the production of toxic free oxygen radicals that cause the corals to loose the algae. These stressed corals have lost their major source of energy and are effectively starving. Some corals can regain their algae and recover; but the increased stress often results in lethal coral diseases or reduced coral reproduction and growth during the next year. Surprisingly although bleaching events have been intensively studied worldwide little is known about the origin of algal rejection or the involved signalling pathways.
Since 2009 the CRIOBE is establishing a holistic approach to elucidate the molecular and physiological coral response to various environmental stresses by using diverse molecular technique, like metabolomics, transcriptomics and cytology. CORALCLIMRESPONSE is embedded in this approach.
The three major expected accomplishments of the project were
1) Molecular characterization of the Symbiodinium population in the host and its dynamics upon stress
2) Cytological staining of the organelles of the polyp and of the Symbiodinium, firstly without and secondly under thermal stress via immunofluorescence microscopy and
3) Comparison of the expression of genes encoding proteins involved in production and degradation of toxic free oxygen radicals notably those involved in organelle protein biosynthesis during a thermal stress experiment and, in collaboration, the identification of secondary metabolites produced by the host and its symbionts in response to the same stress.
The original plan was to conduct thermal stress experiments under natural conditions (in situ) in the lagoon of Moorea. However, the completion of the submersible tent stopped due to time frame and technical problems (Figure1). Instant, the experiments were modified by running the time thermal stress experiments in running seawater aquaria mimicking natural conditions. During the experiment 3-5 coral nubbins (replicates) were taken at each time point and each nubbin was divided into 5 parts for the following analysis: transcriptome (RNA), symbiotic diversity and microbiome (DNA and tissue), organelle function (tissue) and metabolome (tissue) (Figure2). The secondary metabolome is analyzed by Dr. C. Bertrand from the University of Perpignan. Combining the state of the art techniques Fluorescence in situ Hybridisation (FISH), immunofluorescence microscopy, transcriptomics and metabolomics to explore the mechanism of the stress response in one coral is a novelty and has not been done so far. It shows us for the first time a nearly complete picture of the coral stress response. Linking gene expression data with cytology results revealed fundamental information about the dynamic of some organelles in the coral.
Nevertheless, gene expression studies upon stress generally lead to the identification of numbers of up- and down-regulated genes. To enlighten which of these genes are indeed involved in the coral stress response, we decided to enlarge the stress factors. Two additional time series stress experiments were carried out in the same manner as mentioned above, acidification and pesticide contamination. The comparison, in similar conditions, of the coral stress response to three different stressors is unique (Figure3).
Especially, the transcriptomic inter-stress comparison allows us for the first time to precise if the response is stress specific or common.
Our first results are highly promising and the project was extended for another year to continue the data analysis. CORALCLIMRESPONS is expected to show by September 2014 for the first time a nearly complete picture of the corals common and general response stress (cytological, transcriptomic and metabolomic). It will give us a better understanding of the mechanisms taking place during the bleaching process in the coral holobiont. This will lead to the discovery of key genes, which may serve as biomarkers for eutrophication and environmental stress. It will therefore enhance the European excellence in coral scientific community while studying this so far unknown field.
Figure1: Submersible tent in the lagoon of Moorea
Figure2: Interdisciplinary approach to understand the stress response of corals: Each nubbin was divided into 5 parts for the following analysis: a) transcriptome (totalRNA), b) symbiotic diversity and microbiome (DNA and tissue), c) organelle function (tissue) and d) metabolome (tissue).
Figure3: ComparativeTranscriptomics: The data of the transcriptome analysis will be compared for common regulated genes. Furthermore, those selected candidate genes will be compared to all available coral transcriptome databases to elucidate marker genes.
Tropical coral reefs shelter a high rate of marine biodiversity and provide a sizeable amount of ecological services. This ecosystem of interest face tremendous and pervasive challenges from human demography, sky rockets and inherent development pressures, as well as climate change and associated sea level rise. Prospects of coral reefs conservation, critically inevitable, will achieve through the growth of understanding their ecological mechanisms. The basis for the existence of tropical coral reefs is a mutualistic relationship between the coral polyp and its endosymbiotic dinoflagellates, the Symbiodinium sp.. Due to the consequence of global warming coral bleaching became one of the most important threats to coral reefs in the last decade. The higher temperatures and solar radiation disrupt photosynthesis in the coral’s symbiotic algae and result in the production of toxic free oxygen radicals that cause the corals to loose the algae. These stressed corals have lost their major source of energy and are effectively starving. Some corals can regain their algae and recover; but the increased stress often results in lethal coral diseases or reduced coral reproduction and growth during the next year. Surprisingly although bleaching events have been intensively studied worldwide little is known about the origin of algal rejection or the involved signalling pathways.
Since 2009 the CRIOBE is establishing a holistic approach to elucidate the molecular and physiological coral response to various environmental stresses by using diverse molecular technique, like metabolomics, transcriptomics and cytology. CORALCLIMRESPONSE is embedded in this approach.
The three major expected accomplishments of the project were
1) Molecular characterization of the Symbiodinium population in the host and its dynamics upon stress
2) Cytological staining of the organelles of the polyp and of the Symbiodinium, firstly without and secondly under thermal stress via immunofluorescence microscopy and
3) Comparison of the expression of genes encoding proteins involved in production and degradation of toxic free oxygen radicals notably those involved in organelle protein biosynthesis during a thermal stress experiment and, in collaboration, the identification of secondary metabolites produced by the host and its symbionts in response to the same stress.
The original plan was to conduct thermal stress experiments under natural conditions (in situ) in the lagoon of Moorea. However, the completion of the submersible tent stopped due to time frame and technical problems (Figure1). Instant, the experiments were modified by running the time thermal stress experiments in running seawater aquaria mimicking natural conditions. During the experiment 3-5 coral nubbins (replicates) were taken at each time point and each nubbin was divided into 5 parts for the following analysis: transcriptome (RNA), symbiotic diversity and microbiome (DNA and tissue), organelle function (tissue) and metabolome (tissue) (Figure2). The secondary metabolome is analyzed by Dr. C. Bertrand from the University of Perpignan. Combining the state of the art techniques Fluorescence in situ Hybridisation (FISH), immunofluorescence microscopy, transcriptomics and metabolomics to explore the mechanism of the stress response in one coral is a novelty and has not been done so far. It shows us for the first time a nearly complete picture of the coral stress response. Linking gene expression data with cytology results revealed fundamental information about the dynamic of some organelles in the coral.
Nevertheless, gene expression studies upon stress generally lead to the identification of numbers of up- and down-regulated genes. To enlighten which of these genes are indeed involved in the coral stress response, we decided to enlarge the stress factors. Two additional time series stress experiments were carried out in the same manner as mentioned above, acidification and pesticide contamination. The comparison, in similar conditions, of the coral stress response to three different stressors is unique (Figure3).
Especially, the transcriptomic inter-stress comparison allows us for the first time to precise if the response is stress specific or common.
Our first results are highly promising and the project was extended for another year to continue the data analysis. CORALCLIMRESPONS is expected to show by September 2014 for the first time a nearly complete picture of the corals common and general response stress (cytological, transcriptomic and metabolomic). It will give us a better understanding of the mechanisms taking place during the bleaching process in the coral holobiont. This will lead to the discovery of key genes, which may serve as biomarkers for eutrophication and environmental stress. It will therefore enhance the European excellence in coral scientific community while studying this so far unknown field.
Figure1: Submersible tent in the lagoon of Moorea
Figure2: Interdisciplinary approach to understand the stress response of corals: Each nubbin was divided into 5 parts for the following analysis: a) transcriptome (totalRNA), b) symbiotic diversity and microbiome (DNA and tissue), c) organelle function (tissue) and d) metabolome (tissue).
Figure3: ComparativeTranscriptomics: The data of the transcriptome analysis will be compared for common regulated genes. Furthermore, those selected candidate genes will be compared to all available coral transcriptome databases to elucidate marker genes.