Project description:In dinoflagellates, the most unique and divergent nuclear organization among the known diversity of eukaryotes has evolved. The list of highly unusual features of dinoflagellate nuclei and genomes is long -- permanently condensed liquid crystalline chromosomes, in which histones are not the main packaging component, genes organized as very long unidirectional gene arrays, general absence of transcriptional regulation, high abundance of the otherwise very rare DNA modification 5-hydroxymethyluracil (5-hmU), and many others. Most of these fascinating properties were originally identified in the 1970s and 1980s but have received very little attention in recent decades using modern genomic tools. In this work, we address some of the outstanding questions regarding dinoflagellate genome organization by mapping the genome-wide distribution of 5-hmU (using both immunoprecipitation-based and basepair-resolution chemical mapping approaches) and of chromatin accessibility in the genome of the dinoflagellate Breviolum minutum. We find that the 5-hmU modification is preferentially enriched over certain classes of repetitive elements, and also often coincides with the boundaries between gene arrays. It is generally anti-correlated with chromatin accessibility, the levels of which are lower in those regions. We discuss the potential roles of 5-hmU in the functional organization of dinoflagellate genomes and its relationship to the transcriptional landscape of gene arrays.
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:Emergence of the symbiotic lifestyle fostered the immense diversity of all ecosystems on Earth, but symbiosis plays a particularly remarkable role in marine ecosystems. Photosynthetic dinoflagellate endosymbionts power reef ecosystems by transferring vital nutrients to their coral hosts. The mechanisms driving this symbiosis, specifically those which allow hosts to discriminate between beneficial symbionts and pathogens, are not well understood. Here, we uncover that host immune suppression is key for dinoflagellate endosymbionts to avoid elimination by the host using a comparative, model systems approach. Unexpectedly, we find that the clearance of non-symbiotic microalgae occurs by non-lytic expulsion (vomocytosis) and not intracellular digestion, the canonical mechanism used by professional immune cells to destroy foreign invaders. We provide evidence that suppression of TLR signalling by targeting the conserved MyD88 adapter protein has been co-opted for this endosymbiotic lifestyle, suggesting that this is an evolutionarily ancient mechanism exploited to facilitate symbiotic associations ranging from coral endosymbiosis to the microbiome of vertebrate guts.
Project description:Emergence of the symbiotic lifestyle fostered the immense diversity of all ecosystems on Earth, but symbiosis plays a particularly remarkable role in marine ecosystems. Photosynthetic dinoflagellate endosymbionts power reef ecosystems by transferring vital nutrients to their coral hosts. The mechanisms driving this symbiosis, specifically those which allow hosts to discriminate between beneficial symbionts and pathogens, are not well understood. Here, we uncover that host immune suppression is key for dinoflagellate endosymbionts to avoid elimination by the host using a comparative, model systems approach. Unexpectedly, we find that the clearance of non-symbiotic microalgae occurs by non-lytic expulsion (vomocytosis) and not intracellular digestion, the canonical mechanism used by professional immune cells to destroy foreign invaders. We provide evidence that suppression of TLR signalling by targeting the conserved MyD88 adapter protein has been co-opted for this endosymbiotic lifestyle, suggesting that this is an evolutionarily ancient mechanism exploited to facilitate symbiotic associations ranging from coral endosymbiosis to the microbiome of vertebrate guts.
Project description:Cellular mechanisms responsible for the regulation of nutrient exchange, immune responses, and symbiont population growth in the cnidarian-dinoflagellate symbiosis are poorly resolved, particularly with respect to the dinoflagellate symbiont. Here, we characterised proteomic changes in the native symbiont Breviolum minutum during colonisation of its host sea anemone Exaiptasia diaphana (‘Aiptasia’). We also compared the proteome of this native symbiont in the established symbiotic state with that of a non-native symbiont, Durusdinium trenchii. The onset of symbiosis between Aiptasia and B. minutum induced increased accumulation of symbiont proteins associated with acquisition of inorganic carbon and photosynthesis, nitrogen metabolism, micro- and macronutrient starvation, suppression of the host immune responses, tolerance to low pH, and management of oxidative stress. Such responses are consistent with a functional, persistent symbiosis. In contrast, D. trenchii predominantly showed elevated levels of immunosuppressive proteins, consistent with the view that this symbiont is an opportunist that forms a less beneficial, less well-integrated symbiosis with this model anemone. By adding this analyses of the symbiont proteins to the already known responses of the host proteome, our results provide a more holistic view of cellular processes that determine host-symbiont specificity and how differences in symbiont partners, native versus non-native symbionts, may impact the fitness of the cnidarian-dinoflagellate symbiosis in response to thermal stress. This PRIDE entry contains the Breviolum minutum data; Durusdinium trenchii data are uploaded in a separate entry with identical parameters.
Project description:Florida’s coral reefs are currently experiencing a multi-year disease-related mortality event, that has resulted in massive die-offs in multiple coral species. Coral monitoring data and disease prevention/treatment efforts from recent years have identified individual Orbicella faveolata that possess high, moderate, or low resistance to stony coral tissue loss disease (SCTLD). Ninety samples of high, moderate, or low SCTLD resistance were collected from 3 reefs for bottom-up LC-MS/MS analysis (n=30 for each resistance category).
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.