Host and symbiont-specific patterns of gene expression in response to cold stress in the temperate coral Astrangia poculata

The coral Astrangia poculata inhabits hard-bottom environments from the Gulf of Mexico to Massachusetts and withstands large seasonal variation in temperature (–2 to 26 °C). This thermal range and its ability to live in a facultative symbiosis makes this species an ideal model system for investigating stress responses to ocean temperature variation. Although it has been shown that aposymbiotic A. poculata upregulates more genes in response to cold stress than heat stress, the transcriptomic response of the holobiont (coral host and symbiotic algae) to stress is unknown. In this study, we characterize changes in gene expression in both the host and symbionts under cold stress (6ºC) and ambient (12ºC) seawater temperatures. We use RNAseq to visualize how patterns of global gene expression change in response to these temperatures within the transcriptomes of replicate corals (n=10, each temperature) and their symbiont partners. By filtering the holobiont assembly for known coral host and symbiont genes, we contrasted patterns of differential expression (DE) for each partner and the functional processes for each set of DE genes. Differential gene expression analyses revealed that the cnidarian coral host responds strongly to cold stress, while algal symbionts did not have a significant stress response. In the coral host, we found up-regulation of biological processes associated with DNA repair, immunity, and maintaining cellular homeostasis as well as downregulation of mechanisms associated with DNA repair and RNA splicing, indicating inhibition of necessary cellular processes due to environmental stress.