51
|
Kvitt H, Rosenfeld H, Zandbank K, Tchernov D. Regulation of apoptotic pathways by Stylophora pistillata (Anthozoa, Pocilloporidae) to survive thermal stress and bleaching. PLoS One 2011; 6:e28665. [PMID: 22194880 PMCID: PMC3237478 DOI: 10.1371/journal.pone.0028665] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 11/12/2011] [Indexed: 11/25/2022] Open
Abstract
Elevated seawater temperatures are associated with coral bleaching events and related mortality. Nevertheless, some coral species are able to survive bleaching and recover. The apoptotic responses associated to this ability were studied over 3 years in the coral Stylophora pistillata from the Gulf of Eilat subjected to long term thermal stress. These include caspase activity and the expression profiles of the S. pistillata caspase and Bcl-2 genes (StyCasp and StyBcl-2-like) cloned in this study. In corals exposed to thermal stress (32 or 34°C), caspase activity and the expression levels of the StyBcl-2-like gene increased over time (6–48 h) and declined to basal levels within 72 h of thermal stress. Distinct transcript levels were obtained for the StyCasp gene, with stimulated expression from 6 to 48 h of 34°C thermal stress, coinciding with the onset of bleaching. Increased cell death was detected in situ only between 6 to 48 h of stress and was limited to the gastroderm. The bleached corals survived up to one month at 32°C, and recovered back symbionts when placed at 24°C. These results point to a two-stage response in corals that withstand thermal stress: (i) the onset of apoptosis, accompanied by rapid activation of anti-oxidant/anti-apoptotic mediators that block the progression of apoptosis to other cells and (ii) acclimatization of the coral to the chronic thermal stress alongside the completion of symbiosis breakdown. Accordingly, the coral's ability to rapidly curb apoptosis appears to be the most important trait affecting the coral's thermotolerance and survival.
Collapse
Affiliation(s)
- Hagit Kvitt
- Marine Biology Department, The Leon H. Charney School of Marine Sciences, University of Haifa, Mount Carmel, Haifa, Israel.
| | | | | | | |
Collapse
|
52
|
Detournay O, Weis VM. Role of the sphingosine rheostat in the regulation of cnidarian-dinoflagellate symbioses. THE BIOLOGICAL BULLETIN 2011; 221:261-269. [PMID: 22186914 DOI: 10.1086/bblv221n3p261] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The symbiosis between host cnidarians, such as corals and anemones, and their dinoflagellate symbionts is regulated by largely undescribed mechanisms that stabilize the symbiosis during normal conditions but lead to symbiosis breakdown, or cnidarian bleaching, during stress. Previous transcriptomic studies identified the sphingosine rheostat as a putative symbiosis regulatory pathway. The sphingosine rheostat, which includes the sphingolipids sphingosine (Sph) and sphingosine 1-phosphate (S1P), is a key homeostatic cell regulatory pathway known to function in cell fate and immunity in animals. This study explores the role of sphingosine rheostat components in the stability of the symbiotic partnership. The anemone Aiptasia pallida, host to the dinoflagellate Symbiodinium sp., was used to test the hypothesis that S1P promotes symbiosis stability whereas Sph increases bleaching induced by heat stress. Anemones pre-incubated in exogenous S1P and FTY720, a synthetic S1P analog, were partially rescued from heat-stress-induced bleaching. In addition, they displayed a decrease in caspase activity, a measure of apoptosis, compared to controls. In contrast, when anemones were pre-incubated with Sph, both bleaching and caspase activity increased compared to untreated, heat-stressed controls. These data suggest that the sphingosine rheostat may play a role in the balance between stability and dysfunction in cnidarian-dinoflagellate symbioses.
Collapse
Affiliation(s)
- Olivier Detournay
- Department of Zoology, Oregon State University, Corvallis, Oregon 97331, USA.
| | | |
Collapse
|
53
|
Ganot P, Moya A, Magnone V, Allemand D, Furla P, Sabourault C. Adaptations to endosymbiosis in a cnidarian-dinoflagellate association: differential gene expression and specific gene duplications. PLoS Genet 2011; 7:e1002187. [PMID: 21811417 PMCID: PMC3141003 DOI: 10.1371/journal.pgen.1002187] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 06/01/2011] [Indexed: 12/23/2022] Open
Abstract
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.
Collapse
Affiliation(s)
- Philippe Ganot
- Université de Nice-Sophia-Antipolis, Nice, France
- Université Pierre et Marie Curie, Paris, France
- Centre National de la Recherche Scientifique, Roscoff, France
- UMR7138 Systématique, Adaptation, Evolution, Nice, France
| | - Aurélie Moya
- Université de Nice-Sophia-Antipolis, Nice, France
- Université Pierre et Marie Curie, Paris, France
- Centre National de la Recherche Scientifique, Roscoff, France
- UMR7138 Systématique, Adaptation, Evolution, Nice, France
| | - Virginie Magnone
- Université de Nice-Sophia-Antipolis, Nice, France
- Centre National de la Recherche Scientifique, Roscoff, France
- Institut de Pharmacologie Moléculaire et Cellulaire, UMR 6097, Sophia Antipolis, France
| | - Denis Allemand
- Université de Nice-Sophia-Antipolis, Nice, France
- Centre Scientifique de Monaco, Monaco, Monaco
| | - Paola Furla
- Université de Nice-Sophia-Antipolis, Nice, France
- Université Pierre et Marie Curie, Paris, France
- Centre National de la Recherche Scientifique, Roscoff, France
- UMR7138 Systématique, Adaptation, Evolution, Nice, France
| | - Cécile Sabourault
- Université de Nice-Sophia-Antipolis, Nice, France
- Université Pierre et Marie Curie, Paris, France
- Centre National de la Recherche Scientifique, Roscoff, France
- UMR7138 Systématique, Adaptation, Evolution, Nice, France
| |
Collapse
|
54
|
Apoptosis and the selective survival of host animals following thermal bleaching in zooxanthellate corals. Proc Natl Acad Sci U S A 2011; 108:9905-9. [PMID: 21636790 DOI: 10.1073/pnas.1106924108] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
During the past several decades, numerous reports from disparate geographical areas have documented an increased frequency of "bleaching" in reef-forming corals. The phenomenon, triggered by increased sea surface temperatures, occurs when the cnidarian hosts digest and/or expel their intracellular, photosynthetic dinoflagellate symbionts ("zooxanthellae" in the genus Symbiodinium). Although coral bleaching is often followed by the death of the animal hosts, in some cases, the animal survives and can be repopulated with viable zooxanthellae. The physiological factors determining the ability of the coral to survive bleaching events are poorly understood. In this study, we experimentally established that bleaching and death of the host animal involve a caspase-mediated apoptotic cascade induced by reactive oxygen species produced primarily by the algal symbionts. In addition, we demonstrate that, although some corals naturally suppress caspase activity and significantly reduce caspase concentration under high temperatures as a mechanism to prevent colony death from apoptosis, even sensitive corals can be prevented from dying by application of exogenous inhibitors of caspases. Our results indicate that variability in response to thermal stress in corals is determined by a four-element, combinatorial genetic matrix intrinsic to the specific symbiotic association. Based on our experimental data, we present a working model in which the phenotypic expression of this symbiont/host relationship places a selective pressure on the symbiotic association. The model predicts the survival of the host animals in which the caspase-mediated apoptotic cascade is down-regulated.
Collapse
|
55
|
Evidence for an instructive role of apoptosis during the metamorphosis of Hydractinia echinata (Hydrozoa). ZOOLOGY 2011; 114:11-22. [DOI: 10.1016/j.zool.2010.09.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 06/09/2010] [Accepted: 09/19/2010] [Indexed: 12/30/2022]
|
56
|
Pernice M, Dunn SR, Miard T, Dufour S, Dove S, Hoegh-Guldberg O. Regulation of apoptotic mediators reveals dynamic responses to thermal stress in the reef building coral Acropora millepora. PLoS One 2011; 6:e16095. [PMID: 21283671 PMCID: PMC3025915 DOI: 10.1371/journal.pone.0016095] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Accepted: 12/07/2010] [Indexed: 01/21/2023] Open
Abstract
Background Mass coral bleaching is increasing in scale and frequency across the world's coral reefs and is being driven primarily by increased levels of thermal stress arising from global warming. In order to understand the impacts of projected climate change upon corals reefs, it is important to elucidate the underlying cellular mechanisms that operate during coral bleaching and subsequent mortality. In this respect, increased apoptotic cell death activity is an important cellular process that is associated with the breakdown of the mutualistic symbiosis between the cnidarian host and their dinoflagellate symbionts. Methodology/Principal Findings The present study reports the impacts of different stressors (colchicine and heat stress) on three phases of apoptosis: (i) the potential initiation by differential expression of Bcl-2 members, (ii) the execution of apoptotic events by activation of caspase 3-like proteases and (iii) and finally, the cell disposal indicated by DNA fragmentation in the reef building coral Acropora millepora. In corals incubated with colchicine, an increase in caspase 3-like activity and DNA fragmentation was associated with a relative down-regulation of Bcl-2, suggesting that the initiation of apoptosis may be mediated by the suppression of an anti-apoptotic mechanism. In contrast, in the early steps of heat stress, the induction of caspase-dependent apoptosis was related to a relative up-regulation of Bcl-2 consecutively followed by a delayed decrease in apoptosis activity. Conclusions/Significance In the light of these results, we propose a model of heat stress in coral hosts whereby increasing temperatures engage activation of caspase 3-dependent apoptosis in cells designated for termination, but also the onset of a delayed protective response involving overexpression of Bcl-2 in surviving cells. This mitigating response to thermal stress could conceivably be an important regulatory mechanism for cell survival in corals exposed to sudden environmental changes.
Collapse
Affiliation(s)
- Mathieu Pernice
- Coral Reef Ecosystem Laboratory, Global Change Institute, ARC Centre for Excellence in Coral Reef Studies, The University of Queensland, St Lucia, Queensland, Australia.
| | | | | | | | | | | |
Collapse
|
57
|
Saragosti E, Tchernov D, Katsir A, Shaked Y. Extracellular production and degradation of superoxide in the coral Stylophora pistillata and cultured Symbiodinium. PLoS One 2010; 5:e12508. [PMID: 20856857 PMCID: PMC2939047 DOI: 10.1371/journal.pone.0012508] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Accepted: 07/28/2010] [Indexed: 11/19/2022] Open
Abstract
Background Reactive oxygen species (ROS) are thought to play a major role in cell death pathways and bleaching in scleractinian corals. Direct measurements of ROS in corals are conspicuously in short supply, partly due to inherent problems with ROS quantification in cellular systems. Methodology/Principal Findings In this study we characterized the dynamics of the reactive oxygen species superoxide anion radical (O2−) in the external milieu of the coral Stylophora pistillata. Using a sensitive, rapid and selective chemiluminesence-based technique, we measured extracellular superoxide production and detoxification activity of symbiont (non-bleached) and aposymbiont (bleached) corals, and of cultured Symbiodinium (from clades A and C). Bleached and non-bleached Stylophora fragments were found to produce superoxide at comparable rates of 10−11–10−9 mol O2− mg protein−1 min−1 in the dark. In the light, a two-fold enhancement in O2− production rates was observed in non-bleached corals, but not in bleached corals. Cultured Symbiodinium produced superoxide in the dark at a rate of . Light was found to markedly enhance O2− production. The NADPH Oxidase inhibitor Diphenyleneiodonium chloride (DPI) strongly inhibited O2− production by corals (and more moderately by algae), possibly suggesting an involvement of NADPH Oxidase in the process. An extracellular O2− detoxifying activity was found for bleached and non-bleached Stylophora but not for Symbiodinium. The O2− detoxifying activity was partially characterized and found to resemble that of the enzyme superoxide dismutase (SOD). Conclusions/Significance The findings of substantial extracellular O2− production as well as extracellular O2− detoxifying activity may shed light on the chemical interactions between the symbiont and its host and between the coral and its environment. Superoxide production by Symbiodinium possibly implies that algal bearing corals are more susceptible to an internal build-up of O2−, which may in turn be linked to oxidative stress mediated bleaching.
Collapse
Affiliation(s)
- Eldad Saragosti
- Interuniversity Institute for Marine Sciences, Eilat, Israel
- Department of Evolution, Systematics and Ecology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Eilat, Israel
| | - Dan Tchernov
- Interuniversity Institute for Marine Sciences, Eilat, Israel
- Department of Evolution, Systematics and Ecology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Eilat, Israel
| | - Adi Katsir
- Department of Life Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel
| | - Yeala Shaked
- Interuniversity Institute for Marine Sciences, Eilat, Israel
- Fredy & Nadine Herrmann Institute of Earth Sciences, Hebrew University of Jerusalem, Eilat, Israel
- * E-mail:
| |
Collapse
|
58
|
Differential regulation by heat stress of novel cytochrome P450 genes from the dinoflagellate symbionts of reef-building corals. Appl Environ Microbiol 2010; 76:2823-9. [PMID: 20228102 DOI: 10.1128/aem.02984-09] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Exposure to heat stress has been recognized as one of the major factors leading to the breakdown of the coral-alga symbiosis and coral bleaching. Here, we describe the presence of three new cytochrome P450 (CYP) genes from the reef-building coral endosymbiont Symbiodinium (type C3) and changes in their expression during exposure to severe and moderate heat stress conditions. Sequence analysis of the CYP C-terminal region and two conserved domains, the "PERF" and "heme-binding" domains, confirmed the separate identities of the CYP genes analyzed. In order to explore the effects of different heat stress scenarios, samples of the scleractinian coral Acropora millepora were exposed to elevated temperatures incrementally over an 18-h period (rapid thermal stress) and over a 120-h period (gradual thermal stress). After 18 h of gradual heating and incubation at 26 degrees C, the Symbiodinium CYP mRNA pool was approximately 30% larger, while a further 6 degrees C increase to a temperature above the average sea temperature (29 degrees C after 72 h) resulted in a 2- to 4-fold increase in CYP expression. Both rapid heat stress and gradual heat stress at 32 degrees C resulted in 50% to 90% decreases in CYP gene transcript abundance. Consequently, the initial upregulation of expression of CYP genes at moderately elevated temperatures (26 degrees C and 29 degrees C) was followed by a decrease in expression under the greater thermal stress conditions at 32 degrees C. These findings indicate that in the coral-alga symbiosis under heat stress conditions there is production of chemical stressors and/or transcriptional factors that regulate the expression of genes, such as the genes encoding cytochrome P450 monooxygenases, that are involved in the first line of an organism's chemical defense.
Collapse
|
59
|
RODRIGUEZ-LANETTY MAURICIO, HARII SAKI, HOEGH-GULDBERG OVE. Early molecular responses of coral larvae to hyperthermal stress. Mol Ecol 2009; 18:5101-14. [DOI: 10.1111/j.1365-294x.2009.04419.x] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
60
|
Palmer CV, Modi CK, Mydlarz LD. Coral fluorescent proteins as antioxidants. PLoS One 2009; 4:e7298. [PMID: 19806218 PMCID: PMC2752795 DOI: 10.1371/journal.pone.0007298] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2009] [Accepted: 09/08/2009] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND A wide array of fluorescent proteins (FP) is present in anthozoans, although their biochemical characteristics and function in host tissue remain to be determined. Upregulation of FP's frequently occurs in injured or compromised coral tissue, suggesting a potential role of coral FPs in host stress responses. METHODOLOGY/PRINCIPAL FINDINGS The presence of FPs was determined and quantified for a subsample of seven healthy Caribbean coral species using spectral emission analysis of tissue extracts. FP concentration was correlated with the in vivo antioxidant potential of the tissue extracts by quantifying the hydrogen peroxide (H(2)O(2)) scavenging rates. FPs of the seven species varied in both type and abundance and demonstrated a positive correlation between H(2)O(2) scavenging rate and FP concentration. To validate this data, the H(2)O(2) scavenging rates of four pure scleractinian FPs, cyan (CFP), green (GFP), red (RFP) and chromoprotein (CP), and their mutant counterparts (without chromophores), were investigated. In vitro, each FP scavenged H(2)O(2) with the most efficient being CP followed by equivalent activity of CFP and RFP. Scavenging was significantly higher in all mutant counterparts. CONCLUSIONS/SIGNIFICANCE Both naturally occurring and pure coral FPs have significant H(2)O(2) scavenging activity. The higher scavenging rate of RFP and the CP in vitro is consistent with observed increases of these specific FPs in areas of compromised coral tissue. However, the greater scavenging ability of the mutant counterparts suggests additional roles of scleractinian FPs, potentially pertaining to their color. This study documents H(2)O(2) scavenging of scleractinian FPs, a novel biochemical characteristic, both in vivo across multiple species and in vitro with purified proteins. These data support a role for FPs in coral stress and immune responses and highlights the multi-functionality of these conspicuous proteins.
Collapse
Affiliation(s)
- Caroline V Palmer
- School of Biology, Newcastle University, Newcastle upon Tyne, United Kingdom.
| | | | | |
Collapse
|
61
|
Vidal-Dupiol J, Adjeroud M, Roger E, Foure L, Duval D, Mone Y, Ferrier-Pages C, Tambutte E, Tambutte S, Zoccola D, Allemand D, Mitta G. Coral bleaching under thermal stress: putative involvement of host/symbiont recognition mechanisms. BMC PHYSIOLOGY 2009; 9:14. [PMID: 19653882 PMCID: PMC2728513 DOI: 10.1186/1472-6793-9-14] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Accepted: 08/04/2009] [Indexed: 02/02/2023]
Abstract
BACKGROUND Coral bleaching can be defined as the loss of symbiotic zooxanthellae and/or their photosynthetic pigments from their cnidarian host. This major disturbance of reef ecosystems is principally induced by increases in water temperature. Since the beginning of the 1980s and the onset of global climate change, this phenomenon has been occurring at increasing rates and scales, and with increasing severity. Several studies have been undertaken in the last few years to better understand the cellular and molecular mechanisms of coral bleaching but the jigsaw puzzle is far from being complete, especially concerning the early events leading to symbiosis breakdown. The aim of the present study was to find molecular actors involved early in the mechanism leading to symbiosis collapse. RESULTS In our experimental procedure, one set of Pocillopora damicornis nubbins was subjected to a gradual increase of water temperature from 28 degrees C to 32 degrees C over 15 days. A second control set kept at constant temperature (28 degrees C). The differentially expressed mRNA between the stressed states (sampled just before the onset of bleaching) and the non stressed states (control) were isolated by Suppression Subtractive Hybridization. Transcription rates of the most interesting genes (considering their putative function) were quantified by Q-RT-PCR, which revealed a significant decrease in transcription of two candidates six days before bleaching. RACE-PCR experiments showed that one of them (PdC-Lectin) contained a C-Type-Lectin domain specific for mannose. Immunolocalisation demonstrated that this host gene mediates molecular interactions between the host and the symbionts suggesting a putative role in zooxanthellae acquisition and/or sequestration. The second gene corresponds to a gene putatively involved in calcification processes (Pdcyst-rich). Its down-regulation could reflect a trade-off mechanism leading to the arrest of the mineralization process under stress. CONCLUSION Under thermal stress zooxanthellae photosynthesis leads to intense oxidative stress in the two partners. This endogenous stress can lead to the perception of the symbiont as a toxic partner for the host. Consequently, we propose that the bleaching process is due in part to a decrease in zooxanthellae acquisition and/or sequestration. In addition to a new hypothesis in coral bleaching mechanisms, this study provides promising biomarkers for monitoring coral health.
Collapse
Affiliation(s)
- Jeremie Vidal-Dupiol
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| | - Mehdi Adjeroud
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| | - Emmanuel Roger
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| | - Laurent Foure
- Aquarium du Cap d'Agde, 11 rue des 2 freres, 34300 Cap d'Agde, France
| | - David Duval
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| | - Yves Mone
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| | - Christine Ferrier-Pages
- Centre Scientifique de Monaco, Avenue Saint Martin, MC-98000 Monaco-Ville, Principality of Monaco
| | - Eric Tambutte
- Centre Scientifique de Monaco, Avenue Saint Martin, MC-98000 Monaco-Ville, Principality of Monaco
| | - Sylvie Tambutte
- Centre Scientifique de Monaco, Avenue Saint Martin, MC-98000 Monaco-Ville, Principality of Monaco
| | - Didier Zoccola
- Centre Scientifique de Monaco, Avenue Saint Martin, MC-98000 Monaco-Ville, Principality of Monaco
| | - Denis Allemand
- Centre Scientifique de Monaco, Avenue Saint Martin, MC-98000 Monaco-Ville, Principality of Monaco
| | - Guillaume Mitta
- UMR 5244, CNRS EPHE UPVD, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
| |
Collapse
|
62
|
Comprehensive EST analysis of the symbiotic sea anemone, Anemonia viridis. BMC Genomics 2009; 10:333. [PMID: 19627569 PMCID: PMC2727540 DOI: 10.1186/1471-2164-10-333] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Accepted: 07/23/2009] [Indexed: 11/10/2022] Open
Abstract
Background Coral reef ecosystems are renowned for their diversity and beauty. Their immense ecological success is due to a symbiotic association between cnidarian hosts and unicellular dinoflagellate algae, known as zooxanthellae. These algae are photosynthetic and the cnidarian-zooxanthellae association is based on nutritional exchanges. Maintenance of such an intimate cellular partnership involves many crosstalks between the partners. To better characterize symbiotic relationships between a cnidarian host and its dinoflagellate symbionts, we conducted a large-scale EST study on a symbiotic sea anemone, Anemonia viridis, in which the two tissue layers (epiderm and gastroderm) can be easily separated. Results A single cDNA library was constructed from symbiotic tissue of sea anemones A. viridis in various environmental conditions (both normal and stressed). We generated 39,939 high quality ESTs, which were assembled into 14,504 unique sequences (UniSeqs). Sequences were analysed and sorted according to their putative origin (animal, algal or bacterial). We identified many new repeated elements in the 3'UTR of most animal genes, suggesting that these elements potentially have a biological role, especially with respect to gene expression regulation. We identified genes of animal origin that have no homolog in the non-symbiotic starlet sea anemone Nematostella vectensis genome, but in other symbiotic cnidarians, and may therefore be involved in the symbiosis relationship in A. viridis. Comparison of protein domain occurrence in A. viridis with that in N. vectensis demonstrated an increase in abundance of some molecular functions, such as protein binding or antioxidant activity, suggesting that these functions are essential for the symbiotic state and may be specific adaptations. Conclusion This large dataset of sequences provides a valuable resource for future studies on symbiotic interactions in Cnidaria. The comparison with the closest available genome, the sea anemone N. vectensis, as well as with EST datasets from other symbiotic cnidarians provided a set of candidate genes involved in symbiosis-related molecular crosstalks. Altogether, these results provide new molecular insights that could be used as a starting-point for further functional genomics studies.
Collapse
|
63
|
Affiliation(s)
- Virginia M Weis
- Department of Zoology, Oregon State University, Corvallis, OR 97331, USA.
| | | |
Collapse
|
64
|
Weis VM. Cellular mechanisms of Cnidarian bleaching: stress causes the collapse of symbiosis. J Exp Biol 2008; 211:3059-66. [DOI: 10.1242/jeb.009597] [Citation(s) in RCA: 583] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Cnidarian bleaching is a breakdown in the mutualistic symbiosis between host Cnidarians, such as reef building corals, and their unicellular photosynthetic dinoflagellate symbionts. Bleaching is caused by a variety of environmental stressors, most notably elevated temperatures associated with global climate change in conjunction with high solar radiation, and it is a major contributor to coral death and reef degradation. This review examines the underlying cellular events that lead to symbiosis dysfunction and cause bleaching, emphasizing that, to date, we have only some pieces of a complex cellular jigsaw puzzle. Reactive oxygen species (ROS), generated by damage to both photosynthetic and mitochondrial membranes, is shown to play a central role in both injury to the partners and to inter-partner communication of a stress response. Evidence is presented that suggests that bleaching is a host innate immune response to a compromised symbiont, much like innate immune responses in other host–microbe interactions. Finally, the elimination or exit of the symbiont from host tissues is described through a variety of mechanisms including exocytosis, host cell detachment and host cell apoptosis.
Collapse
Affiliation(s)
- Virginia M. Weis
- Department of Zoology, Oregon State University, Corvallis, OR, 97331,USA
| |
Collapse
|
65
|
DeSalvo MK, Voolstra CR, Sunagawa S, Schwarz JA, Stillman JH, Coffroth MA, Szmant AM, Medina M. Differential gene expression during thermal stress and bleaching in the Caribbean coralMontastraea faveolata. Mol Ecol 2008; 17:3952-71. [PMID: 18662230 DOI: 10.1111/j.1365-294x.2008.03879.x] [Citation(s) in RCA: 247] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- M K DeSalvo
- School of Natural Sciences, University of California, Merced, PO Box 2039, Merced, CA 95344, USA
| | | | | | | | | | | | | | | |
Collapse
|
66
|
Fishman Y, Zlotkin E, Sher D. Expulsion of symbiotic algae during feeding by the green hydra--a mechanism for regulating symbiont density? PLoS One 2008; 3:e2603. [PMID: 18596972 PMCID: PMC2432043 DOI: 10.1371/journal.pone.0002603] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Accepted: 05/30/2008] [Indexed: 11/18/2022] Open
Abstract
Background Algal-cnidarian symbiosis is one of the main factors contributing to the success of cnidarians, and is crucial for the maintenance of coral reefs. While loss of the symbionts (such as in coral bleaching) may cause the death of the cnidarian host, over-proliferation of the algae may also harm the host. Thus, there is a need for the host to regulate the population density of its symbionts. In the green hydra, Chlorohydra viridissima, the density of symbiotic algae may be controlled through host modulation of the algal cell cycle. Alternatively, Chlorohydra may actively expel their endosymbionts, although this phenomenon has only been observed under experimentally contrived stress conditions. Principal Findings We show, using light and electron microscopy, that Chlorohydra actively expel endosymbiotic algal cells during predatory feeding on Artemia. This expulsion occurs as part of the apocrine mode of secretion from the endodermal digestive cells, but may also occur via an independent exocytotic mechanism. Significance Our results demonstrate, for the first time, active expulsion of endosymbiotic algae from cnidarians under natural conditions. We suggest this phenomenon may represent a mechanism whereby cnidarians can expel excess symbiotic algae when an alternative form of nutrition is available in the form of prey.
Collapse
Affiliation(s)
- Yelena Fishman
- Department of Cell and Animal Biology, Silberman Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
| | - Eliahu Zlotkin
- Department of Cell and Animal Biology, Silberman Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
| | - Daniel Sher
- Department of Cell and Animal Biology, Silberman Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
- * E-mail:
| |
Collapse
|
67
|
Sunagawa S, Choi J, Forman HJ, Medina M. Hyperthermic stress-induced increase in the expression of glutamate-cysteine ligase and glutathione levels in the symbiotic sea anemone Aiptasia pallida. Comp Biochem Physiol B Biochem Mol Biol 2008; 151:133-8. [PMID: 18602489 DOI: 10.1016/j.cbpb.2008.06.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2008] [Revised: 06/10/2008] [Accepted: 06/10/2008] [Indexed: 11/20/2022]
Abstract
Hyperthermic stress is known to trigger the loss of unicellular algae from a number of symbiotic cnidarians, a phenomenon commonly referred to as bleaching. Oxidative and nitrosative stress have been suggested to play a major role during the process of bleaching, however the underlying molecular mechanisms are still poorly understood. In animals, the intracellular tripeptide glutathione (GSH) is involved in antioxidant defense, redox homeostasis and intracellular redox signaling. Therefore, we tested the hypothesis that hyperthermal stress-induced bleaching in Aiptasia pallida, a model for symbiotic cnidarians, results in increased levels of GSH synthesis. We report the cDNA sequence and functional analysis of the catalytic subunit of glutamate-cysteine ligase (GCLC), which catalyzes the rate-limiting step in GSH biosynthesis. In a time-series experiment, both GCLC gene expression and total GSH levels increased 4- and 1.5-fold, respectively, in response to hyperthermal stress. These results suggest that hyperthermal stress triggers adaptive increases in intracellular GSH biosynthesis in cnidarians as a protective response to oxidative/nitrosative stress. Our results show the conserved function of GCLC and GSH across animals while placing a new perspective on the role of GSH in redox signaling during cnidarian bleaching.
Collapse
Affiliation(s)
- Shinichi Sunagawa
- School of Natural Sciences, University of California, Merced, California, USA
| | | | | | | |
Collapse
|
68
|
Weis VM, Davy SK, Hoegh-Guldberg O, Rodriguez-Lanetty M, Pringle JR. Cell biology in model systems as the key to understanding corals. Trends Ecol Evol 2008; 23:369-76. [PMID: 18501991 DOI: 10.1016/j.tree.2008.03.004] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2007] [Revised: 02/16/2008] [Accepted: 03/11/2008] [Indexed: 01/02/2023]
Abstract
Corals provide the foundation of important tropical reef ecosystems but are in global decline for multiple reasons, including climate change. Coral health depends on a fragile partnership with intracellular dinoflagellate symbionts. We argue here that progress in understanding coral biology requires intensive study of the cellular processes underlying this symbiosis. Such study will inform us on how the coral symbiosis will be affected by climate change, mechanisms driving coral bleaching and disease, and the coevolution of this symbiosis in the context of other host-microbe interactions. Drawing lessons from the broader history of molecular and cell biology and the study of other host-microbe interactions, we argue that a model-systems approach is essential for making effective progress in understanding coral cell biology.
Collapse
Affiliation(s)
- Virginia M Weis
- Department of Zoology, Oregon State University, Corvallis, OR 97331, USA.
| | | | | | | | | |
Collapse
|
69
|
Dunn SR, Schnitzler CE, Weis VM. Apoptosis and autophagy as mechanisms of dinoflagellate symbiont release during cnidarian bleaching: every which way you lose. Proc Biol Sci 2007; 274:3079-85. [PMID: 17925275 PMCID: PMC2293937 DOI: 10.1098/rspb.2007.0711] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Revised: 09/14/2007] [Accepted: 09/17/2007] [Indexed: 01/02/2023] Open
Abstract
Cnidarian bleaching results from the breakdown in the symbiosis between the host cnidarian and its dinoflagellate symbiont. Coral bleaching in recent years has increasingly caused degradation and mortality of coral reefs on a global scale. Although much is understood about the environmental causes of bleaching, the underlying cellular mechanisms of symbiont release that drive the process are just beginning to be described. In this study, we investigated the roles of two cellular pathways, host cell apoptosis and autophagy, in the bleaching process of the symbiotic anemone Aiptasia pallida. Host cell apoptosis was experimentally manipulated using gene knockdown of an anemone caspase by RNA interference, chemical inhibition of caspase using ZVAD-fmk and an apoptosis-inducer wortmannin. Autophagy was manipulated by chemical inhibition using wortmannin or induction using rapamycin. The applications of multiple single treatments resulted in some increased bleaching in anemones under control conditions but no significant drop in bleaching in individuals subjected to a hyperthermic stress. These results indicated that no single pathway is responsible for symbiont release during bleaching. However, when multiple inhibitors were applied simultaneously to block both apoptosis and autophagy, there was a significant reduction in bleaching in heat-stressed anemones. Our results allow us to formulate a model for cellular processes involved in the control of cnidarian bleaching where apoptosis and autophagy act together in a see-saw mechanism such that if one is inhibited the other is induced. Similar interconnectivity between apoptosis and autophagy has previously been shown in vertebrates including involvement in an innate immune response to pathogens and parasites. This suggests that the bleaching response could be a modified immune response that recognizes and removes dysfunctional symbionts.
Collapse
Affiliation(s)
- Simon R Dunn
- Department of Zoology, Oregon State University, Corvallis, OR 97331, USA.
| | | | | |
Collapse
|
70
|
Dunn SR, Phillips WS, Green DR, Weis VM. Knockdown of actin and caspase gene expression by RNA interference in the symbiotic anemone Aiptasia pallida. THE BIOLOGICAL BULLETIN 2007; 212:250-8. [PMID: 17565114 DOI: 10.2307/25066607] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Since the discovery of the ancient eukaryotic process of RNA-mediated gene silencing, the reverse-genetics technique RNA interference (RNAi) has increasingly been used to examine gene function in vertebrate and invertebrate systems. In this study, we report on the use of RNAi, adapted from studies on animal model systems, to manipulate gene expression in a symbiotic marine cnidarian. We describe gene knockdown of actin and of acasp--a cysteine protease, or caspase--in the symbiotic sea anemone Aiptasia pallida. Knockdown was assessed qualitatively with in situ hybridizations for both genes. Quantitative PCR and caspase activity assays were used as a quantitative measure of knockdown for acasp.
Collapse
Affiliation(s)
- Simon R Dunn
- Department of Zoology, Oregon State University, Corvallis, Oregon 97331, USA.
| | | | | | | |
Collapse
|
71
|
Mayfield AB, Gates RD. Osmoregulation in anthozoan-dinoflagellate symbiosis. Comp Biochem Physiol A Mol Integr Physiol 2007; 147:1-10. [PMID: 17317249 DOI: 10.1016/j.cbpa.2006.12.042] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Revised: 12/14/2006] [Accepted: 12/15/2006] [Indexed: 01/17/2023]
Abstract
Endosymbiosis creates a unique osmotic circumstance. Hosts are not only responsible for balancing their internal osmolarity with respect to the external environment, but they must also maintain a compatible osmotic environment for their endosymbionts, which may themselves contribute to the net osmolarity of the host cell through molecular fluxes and/or exchange. Cnidarian hosts that harbor intracellular dinoflagellates (zooxanthellae) are excellent examples of such a symbiosis. These associations are characterized by the exchange of osmotically active compounds, but they are temporally stable under normal environmental conditions indicating that these osmotically driven exchanges are effectively and rapidly regulated. Although we have some knowledge about how asymbiotic anthozoans and algae osmoregulate, our understanding of the physiological mechanisms involved in regulating an intact anthozoan-dinoflagellate symbiosis is poor. Large-scale expulsion of endosymbiotic zooxanthellae, or bleaching, is currently considered to be one of the greatest threats to coral reefs worldwide. To date, there has been little consideration of the osmotic scenarios that occur when these symbioses are exposed to the conditions that normally elicit bleaching, such as increased seawater temperatures and UV radiation. Here we review what is known about osmoregulation and osmotic stress in anthozoans and dinoflagellates and discuss the osmotic implications of exposure to environmental stress in these globally distributed and ecologically important symbioses.
Collapse
Affiliation(s)
- Anderson B Mayfield
- University of Hawaii, Hawaii Institute of Marine Biology, PO Box 1346, Kaneohe, HI 96744, USA.
| | | |
Collapse
|