title: Transcriptomic Analysis of Thermally StressedSymbiodiniumReveals Differential Expression of Stress and Metabolism Genes.
abstract: Endosymbioses between dinoflagellate algae (Symbiodiniumsp.) and scleractinian coral species form the foundation of coral reef ecosystems. The coral symbiosis is highly susceptible to elevated temperatures, resulting in coral bleaching, where the algal symbiont is released from host cells. This experiment aimed to determine the transcriptional changes in culturedSymbiodinium, to better understand the response of cellular mechanisms under future temperature conditions. Cultures were exposed to elevated temperatures (average 31°C) or control conditions (24.5°C) for a period of 28 days. Whole transcriptome sequencing ofSymbiodiniumcells on days 4, 19, and 28 were used to identify differentially expressed genes under thermal stress. A large number of genes representing 37.01% of the transcriptome (∼23,654 unique genes, FDR < 0.05) with differential expression were detected at no less than one of the time points. Consistent with previous studies ofSymbiodiniumgene expression, fold changes across the transcriptome were low, with 92.49% differentially expressed genes at ≤2-fold change. The transcriptional response included differential expression of genes encoding stress response components such as the antioxidant network and molecular chaperones, cellular components such as core photosynthesis machinery, integral light-harvesting protein complexes and enzymes such as fatty acid desaturases. Differential expression of genes encoding glyoxylate cycle enzymes were also found, representing the first report of this inSymbiodinium. As photosynthate transfer fromSymbiodiniumto coral hosts provides up to 90% of a coral's daily energy requirements, the implications of altered metabolic processes from exposure to thermal stress found in this study on coral-Symbiodiniumassociations are unknown and should be considered when assessing the stability of the symbiotic relationship under future climate conditions.
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, TownsvilleQLD, Australia; Comparative Genomics Centre, James Cook University, TownsvilleQLD, Australia.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Gierz
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, TownsvilleQLD, Australia; Evolution, Ecology and Genetics, Research School of Biology, Australian National University, CanberraACT, Australia.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Forêt
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, TownsvilleQLD, Australia; Comparative Genomics Centre, James Cook University, TownsvilleQLD, Australia; ARC Centre of Excellence for Coral Reef Studies, James Cook University, TownsvilleQLD, Australia.
authors.forename: William
authors.initials: W
authors.lastname: Leggat
keywords: RNA-Seq; Symbiodinium; dinoflagellates; gene expression; thermal stress; transcriptome