The genome of Aiptasia , a sea anemone model for coral symbiosis

Abstract

The most diverse marine ecosystems, coral reefs, depend upon a functional symbiosis between a cnidarian animal host (the coral) and intracellular photosynthetic dinoflagellate algae. The molecular and cellular mechanisms underlying this endosymbiosis are not well understood, in part because of the difficulties of experimental work with corals. The small sea anemone Aiptasia provides a tractable laboratory model for investigating these mechanisms. Here we report on the assembly and analysis of the Aiptasia genome, which will provide a foundation for future studies and has revealed several features that may be key to understanding the evolution and function of the endosymbiosis. These features include genomic rearrangements and taxonomically restricted genes that may be functionally related to the symbiosis, aspects of host dependence on alga-derived nutrients, a novel and expanded cnidarian-specific family of putative patternrecognition receptors that might be involved in the animal-algal interactions, and extensive lineage-specific horizontal gene transfer. Extensive integration of genes of prokaryotic origin, including genes for antimicrobial peptides, presumably reflects an intimate association of the animal-algal pair also with its prokaryotic microbiome.coral reefs | endosymbiosis | horizontal gene transfer | dinoflagellate | pattern-recognition receptors C oral reefs form marine-biodiversity hotspots that are of enormous ecological, economic, and aesthetic importance. Coral growth and reef deposition are based energetically on the endosymbiosis between the cnidarian animal hosts and photosynthetic dinoflagellate algae of the genus Symbiodinium, which live in vesicles within the gastrodermal (gut) cells of the animal and typically supply ≥90% of its total energy, while the host provides the algae with a sheltered environment and the inorganic nutrients needed for photosynthesis and growth (1). This tight metabolic coupling allows the holobiont (i.e., the animal host and its microbial symbionts) to thrive in nutrient-poor waters. Although the ecology of coral reefs has been studied intensively, the molecular and cellular mechanisms underlying the critical endosymbiosis remain poorly understood (2). As coral reefs face an ongoing and increasing threat from anthropogenic environmental change (3), new insights into these mechanisms are of critical importance to understanding the resilience and adaptability of coral reefs and thus to the planning of conservation strategies (4).Aiptasia is a globally distributed sea anemone that harbors endosymbiotic Symbiodinium like its Class Anthozoa relatives the stony corals ( Fig. 1 and SI Appendix, Fig. S1A) (4, 5). Aiptasia has a range of polyp sizes convenient for experimentation and is easily grown in laboratory culture, where it reproduces both asexually (so that large clonal populations can be obtained) and sexually (allowing experiments on larvae and potentially genetic studies), and it can be maintained indefinitely in an aposymbiotic (dinoflagellate-free) state and ...

Adaptation to deep-sea chemosynthetic environments as revealed by mussel genomes

“…The target microbes carry signature molecules on their surface, which are recognized by the transmembrane pattern-recognition receptors (PRRs) of the host 19 . Among the PRRs in B. platifrons, there was a significant expansion of genes with an immunoglobin (Ig) domain and genes with an fibrinogen domain, both of which are critical in allowing the sea anemone Aiptasia to recognize its dinoflagellate symbiont 20 . In addition, peptidoglycan-recognition proteins (PGRPs) that can bind with peptidoglycan 21 on the bacterial cell wall were also expanded in the genome of B. platifrons.…”

Importance, Destruction and Recovery of Coral Reefs

“…Coral reefs form marine-biodiversity hotspots of enormous ecological, economic, and aesthetic importance that rely energetically on a functional symbiosis between the coral animal and a photosynthetic alga. [13] Such as the relation between coral and marine organism, the Corals depend upon a functional symbiosis between a cnidarian animal host (the coral) and intracellular photosynthetic dinoflagellate algae. [13] Coral reefs are the most biologically diverse of shallow water marine ecosystems.…”

“…[13] Such as the relation between coral and marine organism, the Corals depend upon a functional symbiosis between a cnidarian animal host (the coral) and intracellular photosynthetic dinoflagellate algae. [13] Coral reefs are the most biologically diverse of shallow water marine ecosystems. [14] Importance, destruction and recovery of coral reefs …”

Similar ratios of introns to intergenic sequence across animal genomes

“…Assembly and annotation for Exaiptasia pallida (formerly Aiptasia sp.) (Baumgarten et al 2015) were downloaded from http://reefgenomics.org. Assembly and annotation for Oikopleura dioica (Denoeud et al 2010) were downloaded from Genoscope (http://www.genoscope.…”