Project description:Coral reefs are declining globally. Temperature anomalies disrupt coral-algal symbioses at the molecular level, causing bleaching and mortality events. In terrestrial mutualisms, diversity in pairings of host and symbiont individuals (genotypes) results in ecologically and evolutionarily relevant stress response differences. The extent to which such intraspecific diversity provides functional variation in coral-algal systems is unknown. Here we assessed functional diversity among unique pairings of coral and algal individuals (holobionts). We targeted six genetically distinct Acropora palmata coral colonies that all associated with a single, clonal Symbiodinium ‘fitti’ strain in a natural common garden. No other species of algae or other strains of S. ‘fitti’ could be detected in host tissues. When colony branches were experimentally exposed to cold stress, host genotype influenced the photochemical efficiency of the symbiont strain, buffering the stress response to varying degrees. Gene expression differences among host individuals with buffered vs. non-buffered symbiont responses included biochemical pathways that mediate iron availability and oxygen stress signaling—critical components of molecular interactions with photosynthetic symbionts. Spawning patterns among hosts reflected symbiont performance differences under stress. These data are some of the first to indicate that genetic interactions below the species level affect coral holobiont performance. Intraspecific diversity serves as an important but overlooked source of physiological variation in this system, contributing raw material available to natural selection. Note: in the final publication, only ambient and cold treatments are discussed, but there was an additional hot treatment for each genotype at 34C. Most colonies expired after 6 hours, so PAM data could not be collected. The microarray data from 3.5 hours are included here.
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:Since the discovery of Chromera velia as a novel coral-associated microalga, this organism has attracted interest because of its unique evolutionary position between the photosynthetic dinoflagellates and the parasitic apicomplexans. The nature of the relationship between Chromera and its coral host is controversial. Is it a mutualism, from which both participants benefit, or is Chromera a parasite, harming its host? To better understand the interaction, larvae of the common Indo-Pacific reef-building coral Acropora digitifera were experimentally infected with Chromera and the impact on the host transcriptome assessed at 4, 12, and 48 h post-infection using Illumina RNA-Seq technology. The transcriptomic response of the coral to Chromera was complex and implies that host immunity is strongly suppressed, and both phagosome maturation and the apoptotic machinery modified. These responses differ markedly from those described for infection with a competent strain of the coral symbiont Symbiodinium, instead resembling those of vertebrate hosts to parasites and/or pathogens such as Mycobacterium tuberculosis. Consistent with ecological studies suggesting that the association may be accidental, the transcriptional response of A. digitifera larvae leads us to conclude that Chromera is more likely to be a coral parasite, commensal, or accidental bystander, but certainly not a beneficial mutualist
Project description:We subjected three inshore and four offshore genotypes of the coral Orbicella faveolata to 30, 31, 32, or 33ºC for 31 days and measured photochemical efficiency (Fv/Fm), the types and relative abundance of dinoflagellate endosymbionts, and gene expression of the host and symbiont. All inshore coral genotypes, regardless of symbiont type, were significantly more thermotolerant than offshore genotypes based on declines in Fv/Fm. The most heat-tolerant inshore genotype (In1) was dominated by Durusdinium trenchii; all other genotypes were Breviolum-dominated, suggesting local adaptation or acclimatization contributes to the heat tolerance of inshore genotypes. After 31 days of heat stress, all coral genotypes (except In2) had lost most of their Breviolum and became dominated by D. trenchii. Host genotype In1 presented unique expression patterns of genes involved in heat shock response, immunity, and protein degradation. There were few changes in the symbiont transcriptomes of inshore corals under heat stress, but significant changes in symbiont gene expression from the offshore colonies, including increases in ribosomal and photosynthetic proteins. These data show that the differential thermotolerance between inshore and offshore O. faveolata in the Florida Keys is associated with statistically significant differences in both host and symbiont gene expression that provide insights into the mechanisms underlying holobiont heat tolerance.
Project description:Coral reefs worldwide are facing rapid decline due to coral bleaching. However, knowledge of the physiological characteristics and molecular mechanisms of coral symbionts respond to stress is scarce. Here, metagenomic and metaproteomic approach were utilized to shed light on the changes in the composition and functions of coral symbionts during coral bleaching. The results demonstrated that coral bleaching significantly affected the composition of symbionts, with bacterial communities dominating in bleached corals. Difference analysis of gene and protein indicated that symbiont functional disturbances in response to heat stress, resulting in abnormal energy metabolism that could potentially compromise symbiont health and resilience. Furthermore, our findings highlighted the highly diverse microbial communities of coral symbionts, with beneficial bacteria provide critical services to corals in stress responses, while pathogenic bacteria drive coral bleaching. This study provides comprehensive insights into the complex response mechanisms of coral symbionts under thermal stress and offers fundamental data for future monitoring of coral health.
Project description:Background: Anthozoan cnidarians are amongst the simplest animals at the tissue level of organization, but are surprisingly complex and vertebrate-like in terms of gene repertoire. As major components of tropical reef ecosystems, the stony corals are anthozoans of particular ecological significance. To better understand the molecular bases of both cnidarian development in general and coral-specific processes such as skeletogenesis and symbiont acquisition, microarray analysis was carried out through the period of early development – when skeletogenesis is initiated, and symbionts are first acquired. Methodology/ Principal Findings: Of approximately 5600 unique genes represented on the microarrays, 1084 were differentially expressed (P <0.05) in comparisons between four different stages of coral development, spanning key developmental transitions. Genes of likely relevance to the processes of settlement, metamorphosis, calcification and interaction with symbionts were characterised further and their spatial expression patterns investigated using whole-mount in situ hybridisation. Conclusions/Significance: This study is the first large-scale investigation of developmental gene expression for any cnidarian, and has provided candidate genes for key roles in many aspects of coral biology, including calcification, metamorphosis and symbiont uptake. One surprising finding is that some of these genes have clear counterparts in higher animals but are not present in the closely-related sea anemone Nematostella. A second conclusion is that coral-specific processes (i.e. traits which distinguish corals from their close relatives) may be analogous to similar processes in distantly related organisms. This first large-scale application of microarray analysis demonstrates the potential of this approach for investigating many aspects of coral biology, including the effects of stress and disease. Keywords: developmental
Project description:Background: The molecular machinery underpinning the establishment of this relationship is not well understood. This is especially true of the symbiont side, as previous attempts to understand the interaction between coral larvae and Symbiodiniaceae have focused nearly exclusively on the host Results: In the current study, we utilised dual RNA-seq approach to study both symbiont and coral transcriptomes during symbiosis establishment. The transcriptomic response of C. goreaui to the symbiotic state was complex, the most obvious feature of which was extensive and generalized downregulation of gene expression. Included in this “symbiosis-derived transcriptional repression” were a range of stress response and immune-related genes. In contrast, a range of genes implicated in metabolism were upregulated in the symbiotic state. Consistent with previous ecological studies, this transcriptomic response of C. goreaui suggests that active translocation of metabolites to the host may begin early in the colonization process, and thus that the mutualistic relationship is established at the larval stage. The coral data imply the involvement of some SCRiP family members in the colonisation process and support the hypothesis that immune-suppression and arrest of phagosome maturation play important roles during the establishment of compatible symbioses. Conclusions: This study provides novel insights into the transcriptomic remodelling that occurs in C. goreaui during transition to a symbiotic lifestyle, with important implications for understanding the establishment of symbiosis between corals and their dinoflagellate partners.
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:The emergence of genomic tools for reef-building corals and symbiotic anemones comes at a time when alarming losses in coral cover are being observed worldwide. These tools hold great promise in elucidating novel and unforeseen cellular processes underlying the successful mutualism between corals and their algal endosymbionts (Symbiodinium spp.). Since thermal stress triggers a breakdown in the symbiosis (coral bleaching), measuring the transcriptomic response to thermal stress-induced bleaching offers an extraordinary view of the cellular processes specific to coral-algal symbioses. In the present study, we utilized a cDNA microarray containing 2,059 genes of the Caribbean Elkhorn coral Acropora palmata to identify genes differentially expressed upon thermal stress. Fragments from four separate colonies were exposed to elevated temperature (3˚C increase) for two days, and samples were frozen for microarray analysis after 24 and 48 hours. Fragments experienced a 60% reduction in algal cell density after two days. 204 genes were differentially expressed in samples collected one day after thermal stress; in samples collected after two days, 104 genes. Annotations of the differentially expressed genes indicate a conserved cellular stress response in A. palmata involving: 1) growth arrest; 2) chaperone activity; 3) nucleic acid stabilization and repair; and 4) the removal of damaged macromolecules. Other differentially expressed processes include sensory perception, metabolite transfer between host and symbiont, nitric oxide signaling, and modifications to the actin cytoskeleton and extracellular matrix. The results are also compared to those from a previous coral microarray study of thermal stress in Montastraea faveolata.