Coral bleaching under thermal stress: putative involvement of host/symbiont recognition mechanisms
Open Access
- 4 August 2009
- journal article
- Published by Springer Science and Business Media LLC in BMC Physiology
- Vol. 9 (1), 14
- https://doi.org/10.1186/1472-6793-9-14
Abstract
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. In our experimental procedure, one set of Pocillopora damicornis nubbins was subjected to a gradual increase of water temperature from 28°C to 32°C over 15 days. A second control set kept at constant temperature (28°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. 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.Keywords
This publication has 76 references indexed in Scilit:
- Differential gene expression during thermal stress and bleaching in the Caribbean coral Montastraea faveolataMolecular Ecology, 2008
- Heat Stress Stimulates Nitric Oxide Production in Symbiodinium microadriaticum: A Possible Linkage between Nitric Oxide and the Coral Bleaching PhenomenonPlant and Cell Physiology, 2008
- An ancient and variable mannose-binding lectin from the coral Acropora millepora binds both pathogens and symbiontsDevelopmental & Comparative Immunology, 2008
- Apoptosis and autophagy as mechanisms of dinoflagellate symbiont release during cnidarian bleaching: every which way you loseProceedings Of The Royal Society B-Biological Sciences, 2007
- Coral reef bleaching and global climate change: Can corals survive the next century?Proceedings of the National Academy of Sciences of the United States of America, 2007
- Oxidative stress and apoptotic events during thermal stress in the symbiotic sea anemone, Anemonia viridisThe FEBS Journal, 2006
- A New C-Type Lectin Similar to the Human Immunoreceptor DC-SIGN Mediates Symbiont Acquisition by a Marine NematodeApplied and Environmental Microbiology, 2006
- Climate change, coral bleaching and the future of the world's coral reefsMarine and Freshwater Research, 1999
- Coral bleaching: causes and consequencesCoral Reefs, 1997
- Structure—function relationships in the receptor for urokinase‐type plasminogen activator Comparison to other members of the Ly‐6 family and snake venom α‐neurotoxinsFEBS Letters, 1994