Analysis of an EST library from the dinoflagellate (Symbiodinium sp.) symbiont of reef‐building corals¹

Abstract

Dinoflagellates (Symbiodinium sp. Freud.) are an obligatory endosymbiont of the reef-building corals. Recent changes to the environment surrounding coral reefs (e.g., global warming) have demonstrated that this endosymbiotic relationship between corals and Symbiodinium is particularly sensitive to environmental changes. Therefore, understanding gene expression patterns of Symbiodinium is critical to understanding why coral reefs are susceptible to global climate change. This study identified 1456 unique expression sequence tags (ESTs) generated for Symbiodinium (clade C3) from the staghorn coral Acropora aspera following exposure to a variety of stresses. Of these, only 10% matched previously reported dinoflagellate ESTs, suggesting that the conditions used in the construction of the library resulted in a novel transcriptome. The function of 561 (44%) of these ESTs could be identified. The majority of these genes coded for proteins involved in posttranslational modification, protein turnover, and chaperones (12.3%); energy production and conversion (12%); or an unknown function (18.6%). The most common transcript found was a homologue to a bacterial protein of unknown function. This algal protein is targeted to the chloroplast and is present in those phototrophs that acquired plastids from the red algal lineage. An additional 48 prokaryote-like proteins were also identified, including the first glycerol-phosphate:phosphate antiporter from dinoflagellates. A protein with similarity to the fungi-archael-bacterial heme catalase peroxidases was also found. A variety of stress genes, in particular heat-shock proteins and proteins involved in ubiquitin cascades, were also identified. This study is the first transcriptome from the unicellular component of a eukaryote-eukaryote symbiosis.

The effect of thermal history on the susceptibility of reef-building corals to thermal stress

“…This is not surprising given that acclimation in the holobiont can involve the coral host, Symbiodinium, or a combination of both (Dove, 2004). Both corals (Kortschak et al, 2003) and Symbiodinium (Leggat et al, 2007) have been shown to possess a wide variety of genes that encode for stress response proteins (e.g. heat shock proteins, superoxide dismutase, ubiquitin etc.…”

A single-cell view of ammonium assimilation in coral–dinoflagellate symbiosis

“…By doing so, the coral host would not only protect its tissue from high and toxic environmental ammonium load, but would also facilitate the transport of ammonium to the dinoflagellate cells, thus enabling a more efficient use of the pulse of enriched seawater. Once ammonium is present in the direct environment of symbiotic dinoflagellates, its assimilation depends on the physiological properties of the algae including (i) the activity of ammonium transporters, as suggested by the presence of several sequences encoding such transporters in an expressed sequence tag library from Symbiodinium (Leggat et al, 2007) and (ii) the concerted action of several enzymes in dinoflagellate cells such as glutamate dehydrogenase, GS and GOGAT (Summons and Osmond, 1981;Summons et al, 1986).…”

Unfolding the secrets of coral–algal symbiosis

“…Sanger sequences (Leggat et al, 2007) for conserved HSP70 and HSP90 genes (Rosic et al, 2011a) and novel polymorphic hemoglobin-like proteins (Rosic et al, 2013) with the assemblies. The results of BLASTn and BLASTx alignments, with stringent E-values and high bit scores, confirmed the presence of these genes in the de novo assemblies of all four transcriptomes presented here (Supplementary Table S3).…”