Project description:A mutualistic relationship between reef-building corals and endosymbiotic algae (Symbiodinium spp.) forms the basis for the existence of coral reefs. Genotyping tools for Symbiodinium spp. have added a new level of complexity to studies concerning cnidarian growth, nutrient acquisition, and stress. For example, the response of the coral holobiont to thermal stress is connected to the host-Symbiodinium genotypic combination, as different partnerships can have different bleaching susceptibilities. If, and to what extent, differences in algal symbiont clade contents can exert effects on the coral host transcriptome is currently unknown. In this study, we monitored algal physiological parameters and profiled the coral host transcriptional responses in acclimated, thermally stressed, and recovered coral fragments using a custom cDNA gene expression microarray. Combining these analyses with results from algal and host genotyping revealed a striking symbiont effect on both the acclimated coral host transcriptome and the magnitude of the thermal stress response. This is the first study that links coral host transcriptomic patterns to the clade content of their algal symbiont community. Our data provide a critical step to elucidating the molecular basis of the apparent variability seen among different coral-algal partnerships.
Project description:Using transcriptomics, we show that Symbiodinium acclimation to elevated temperature involves up-regulated expression of meiosis genes followed by up-regulated expression of numerous reactive oxygen species scavenging genes and molecular chaperone genes. Our study connects Symbiodinium transcriptional regulation with physiological heat stress responses as well as known bleaching responses of corals harboring these same Symbiodinium. By uncovering these critical links, we greatly advance understanding of the bleaching susceptibility of corals, which is a key process responsible for global coral reef health.
Project description:Given the overwhelming evidence that symbiont genotypes differentially affect host processes such as growth, bleaching susceptibility, and nutrient acquisition, we set out to measure gene expression differences in fragments of Montastraea faveolata harboring two different clades of Symbiodinium. On the reefs near Puerto Morelos, México, colonies of M. faveolata are known to shift algal symbiont clade with depth, often associating with clade A at the top, clade B in the middle, and clade C near the bottom of the colony. By measuring photosynthetic efficiency and gene expression in control and heat-stressed fragments containing either clade B, clade C, or a mix of both, we found that: 1) the algal response to thermal stress is due to both host and algal factors; 2) fragments of M. faveolata express different genes in response to sub-bleaching thermal stress depending on algal genotype; 3) the overall effect of heat stress on coral gene expression is less significant than the effect of housing different zooxanthellae types. Overall, we present convincing evidence that different Symbiodinium clades may be functionally distinct, which in turn, greatly influences host gene expression.
Project description:The declining health of coral reefs worldwide is likely to intensify in response to continued anthropogenic disturbance from coastal development, pollution, and climate change. In response to these stresses, reef-building corals may exhibit bleaching, which marks the breakdown in symbiosis between coral and zooxanthellae. Mass coral bleaching due to elevated water temperature can devastate coral reefs on a large geographic scale. In order to understand the molecular and cellular basis of bleaching in corals, we have measured gene expression changes associated with thermal stress and bleaching using a cDNA microarray containing 1,310 genes of the Caribbean coral Montastraea faveolata. In a first experiment, we identified differentially expressed genes by comparing experimentally bleached M. faveolata fragments to control non-heat-stressed fragments. We also identified differentially expressed genes during a time course experiment with four time points across nine days. Results suggest that thermal stress and bleaching in M. faveolata affect the following processes: oxidative stress, Ca2+ homeostasis, cytoskeletal organization, cell death, calcification, metabolism, protein synthesis, heat shock protein activity, and transposon activity. These results represent the first large-scale transcriptomic study focused on revealing the cellular foundation of thermal stress-induced coral bleaching. We postulate that oxidative stress in thermal-stressed corals causes a disruption of Ca2+ homeostasis, which in turn leads to cytoskeletal and cell adhesion changes, decreased calcification, and the initiation of cell death via apoptosis and necrosis. Keywords: thermal stress response, time course, coral bleaching
Project description:The declining health of coral reefs worldwide is likely to intensify in response to continued anthropogenic disturbance from coastal development, pollution, and climate change. In response to these stresses, reef-building corals may exhibit bleaching, which marks the breakdown in symbiosis between coral and zooxanthellae. Mass coral bleaching due to elevated water temperature can devastate coral reefs on a large geographic scale. In order to understand the molecular and cellular basis of bleaching in corals, we have measured gene expression changes associated with thermal stress and bleaching using a cDNA microarray containing 1,310 genes of the Caribbean coral Montastraea faveolata. In a first experiment, we identified differentially expressed genes by comparing experimentally bleached M. faveolata fragments to control non-heat-stressed fragments. We also identified differentially expressed genes during a time course experiment with four time points across nine days. Results suggest that thermal stress and bleaching in M. faveolata affect the following processes: oxidative stress, Ca2+ homeostasis, cytoskeletal organization, cell death, calcification, metabolism, protein synthesis, heat shock protein activity, and transposon activity. These results represent the first large-scale transcriptomic study focused on revealing the cellular foundation of thermal stress-induced coral bleaching. We postulate that oxidative stress in thermal-stressed corals causes a disruption of Ca2+ homeostasis, which in turn leads to cytoskeletal and cell adhesion changes, decreased calcification, and the initiation of cell death via apoptosis and necrosis. Keywords: thermal stress response; coral bleaching
Project description:The declining health of coral reefs worldwide is likely to intensify in response to continued anthropogenic disturbance from coastal development, pollution, and climate change. In response to these stresses, reef-building corals may exhibit bleaching, which marks the breakdown in symbiosis between coral and zooxanthellae. Mass coral bleaching due to elevated water temperature can devastate coral reefs on a large geographic scale. In order to understand the molecular and cellular basis of bleaching in corals, we have measured gene expression changes associated with thermal stress and bleaching using a cDNA microarray containing 1,310 genes of the Caribbean coral Montastraea faveolata. In a first experiment, we identified differentially expressed genes by comparing experimentally bleached M. faveolata fragments to control non-heat-stressed fragments. We also identified differentially expressed genes during a time course experiment with four time points across nine days. Results suggest that thermal stress and bleaching in M. faveolata affect the following processes: oxidative stress, Ca2+ homeostasis, cytoskeletal organization, cell death, calcification, metabolism, protein synthesis, heat shock protein activity, and transposon activity. These results represent the first large-scale transcriptomic study focused on revealing the cellular foundation of thermal stress-induced coral bleaching. We postulate that oxidative stress in thermal-stressed corals causes a disruption of Ca2+ homeostasis, which in turn leads to cytoskeletal and cell adhesion changes, decreased calcification, and the initiation of cell death via apoptosis and necrosis. Keywords: thermal stress response; coral bleaching 5 control and 5 heat-stressed RNA samples were hybridized in a 5-replicate dye-swap design (10 total hyb's).
Project description:The declining health of coral reefs worldwide is likely to intensify in response to continued anthropogenic disturbance from coastal development, pollution, and climate change. In response to these stresses, reef-building corals may exhibit bleaching, which marks the breakdown in symbiosis between coral and zooxanthellae. Mass coral bleaching due to elevated water temperature can devastate coral reefs on a large geographic scale. In order to understand the molecular and cellular basis of bleaching in corals, we have measured gene expression changes associated with thermal stress and bleaching using a cDNA microarray containing 1,310 genes of the Caribbean coral Montastraea faveolata. In a first experiment, we identified differentially expressed genes by comparing experimentally bleached M. faveolata fragments to control non-heat-stressed fragments. We also identified differentially expressed genes during a time course experiment with four time points across nine days. Results suggest that thermal stress and bleaching in M. faveolata affect the following processes: oxidative stress, Ca2+ homeostasis, cytoskeletal organization, cell death, calcification, metabolism, protein synthesis, heat shock protein activity, and transposon activity. These results represent the first large-scale transcriptomic study focused on revealing the cellular foundation of thermal stress-induced coral bleaching. We postulate that oxidative stress in thermal-stressed corals causes a disruption of Ca2+ homeostasis, which in turn leads to cytoskeletal and cell adhesion changes, decreased calcification, and the initiation of cell death via apoptosis and necrosis. Keywords: thermal stress response, time course, coral bleaching Time course with 4 time points and 4 biological replicates per time point. Each biological replicate at each time point was hybridized to a pooled reference control sample containing RNA from all control non-heat-stressed coral fragments.
Project description:Abstract The coral–dinoflagellate symbiosis is increasingly disrupted by global and local anthropogenic stressors. Coral bleaching is primarily a result of high sea surface temperatures, while eutrophication is associated with reef ecosystem degradation. Excess inorganic nitrogen relative to phosphate has been proposed to directly sensitise corals to thermal bleaching and accelerate reef decline. We assessed the proteomic response of the dinoflagellate coral symbiont Symbiodinium microadriaticum to elevated temperatures under multiple nutrient conditions by mass spectrometry. Elevated temperatures resulted in reductions of many chloroplast proteins, particularly light-harvesting complexes, with simultaneous increases in chaperone proteins. N:P imbalance had a larger effect on the proteome than temperature, but the biological processes and proteins responding to each stressor largely overlapped. The proteomes were highly similar at low N:P ratios but were strongly affected by phosphate starvation. High N:P ratios inhibited cell division, reflected by changes in proteins involved in protein translation. Imbalanced N:P did not increase sensitivity to high temperatures as measured by physiological means; however, imbalanced N:P strongly upregulated cell redox homeostasis proteins at high temperatures. As redox balance is critical during thermal bleaching, these data provide insight into the mechanisms of cellular responses to thermal and multiple stresses in the coral–dinoflagellate symbiosis.
Project description:Coral reefs are based on the symbiotic relationship between corals and photosynthetic dinoflagellates of the genus Symbiodinium. We followed gene expression of coral larvae of Acropora palmata and Montastraea faveolata after exposure to Symbiodinium strains that differed in their ability to establish symbioses. We show that the coral host transcriptome remains almost unchanged during infection by competent symbionts, but is massively altered by symbionts that fail to establish symbioses. Our data suggest that successful coral-algal symbioses depend mainly on the symbionts' ability to enter the host in a stealth manner rather than a more active response from the coral host.