Abstract
Dinoflagellate endosymbionts from the family Symbiodiniaceae form a mutualistic relationship with corals. However, this partnership is vulnerable to temperature stress, which can result in coral bleaching. In this study, we sequenced the metatranscriptome of symbionts (dominated by ITS2 type C3u) associated with the common scleractinian coral, Acropora digitifera, from Bolinao, Pangasinan, northwestern Philippines, to elucidate their genetic complement and stress response mechanisms. The assembled metatranscriptome revealed a rich repertoire of genes for the utilization of nutrients and metabolic exchange with the host, as well as genes that provide protection against cellular damage. Exposure of the algal endosymbionts to 31°C for 12 h induced global changes in the transcriptome profile. While transcripts involved in cell signaling, cytoskeletal organization, and rRNA processing were upregulated, downregulation of transcripts related to translation, proteolysis, lipid storage, and immune response indicate vulnerability to acute thermal stress. Some of these stress responsive transcripts were predicted to be under microRNA (miRNA) regulation. These findings reveal conserved hallmarks of coral-algal symbiosis and provide insights into the genetic potential and acute thermal stress response of a common symbiont of corals in the region.
Highlights
Reef building corals host dinoflagellate endosymbionts of the family Symbiodiniaceae in their tissues (Kirk and Weis, 2016)
We note that because the cultures were not derived by single cell isolation, they represent the community of symbionts associated with the coral and may include coralassociated bacteria and some single-celled eukaryotes that were not effectively removed by the filtering and centrifugation steps
Sequencing of the metatranscriptome of the ITS2 type C3 symbionts associated with A. digitifera revealed a rich complement of genes for the maintenance of symbiosis and environmental defense
Summary
Reef building corals host dinoflagellate endosymbionts of the family Symbiodiniaceae in their tissues (Kirk and Weis, 2016). These symbionts provide the majority of the energetic requirements of the coral and are critical for the maintenance of coral health (Muscatine and Porter, 1977). Corals in the Persian Gulf or those that have experienced bleaching events usually host symbionts from genus Durusdinium, which are well-adapted for growth and photosynthesis at high temperature (Stat et al, 2013; Hume et al, 2015). Elucidating the diversity of symbionts in corals from different regions and their physiological responses to stress will be essential for predicting coral bleaching susceptibility
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