Transcriptional response of the azooxanthellate octocoral Scleronephthya gracillimum to seawater acidification and thermal stress.

The stress responses to increased seawater temperature and marine acidification were investigated using a microarray to reveal transcriptional changes in S. gracillimum. For the study, corals were exposed to different stress experiments; high temperature only (26 °C, 28 °C and 30 °C), low-pH only (pH 7.5, pH 7.0 and pH 6.5) and dual stress experiments (28 °C + pH 7.8, 28 °C + pH 7.5 and 28 °C + pH 7.0), mortality and morphological changes in 24 h exposure experiments were investigated. The survival rates of each experimental group were observed. The gene expression changes in single and dual stress exposed coals were measured and the differentially expressed genes were classified with gene ontology analysis. The top three enriched gene ontology terms of DEGs in response to dual stress were metal ion binding (23.4%), extracellular region (17.2%), and calcium ion binding (12.8%). The gene showing the greatest increase in expression as a response to the dual stress was hemagglutinin/amebocyte aggregation factor, followed by interferon-inducible GTPase 5 and the gene showing the greatest decrease as a response to the dual stress was Fas-associating death domain-containing protein, followed by oxidase 2. These results represented the transcriptomic study focused on the stress responses of the temperate asymbiotic soft coral exposed to single and dual stresses. The combined effect of thermal and acidification stress on corals triggered the negative regulation of ion binding and extracellular matrix coding genes and these genes might serve as a basis for research into coral-specific adaptations to stress responses and global climate change.