Euphyllia paradivisa Transcriptome or Gene expression

The profound mutualistic symbiosis between corals and their endosymbiotic counterpart's Symbiodinium algae has been challenged by the increase in sea water temperatures, and consequent coral bleaching. For this study, as an approach to characterization of the heat-stress response of the holobiont, we generated vital apo-symbiotic Euphyllia paradivisa corals that lack the endosymbiotic algae. We then analyzed the gene expression of these apo-symbionts in order to investigate the effect of the algal presence on the tolerance and fitness of the coral. To achieve our objectives, we used high throughput sequencing techniques aligned with various bioinformatic tools to compare the response of symbiotic and apo-symbiotic E. paradivisa to elevated heat-stress. We also utilized literature-derived lists of “symbiosis differentially-expressed genes” and “coral heat-stress genes” in order to compare the different treatments. The results showed that the symbiotic and apo-symbiotic samples were segregated into two separate groups. In support of this observation, several Gene Ontologies (GO) were found to be enriched differentially in the symbiotic and apo-symbiotic corals. Our findings suggest that the presence of algal symbionts has a greater negative impact on the coral host than the environmental temperature conditions experienced by the holobiont. We identified 28°C as the peak of the stress reaction in the symbiotic corals, with the highest number of differentially expressed genes associated with a response to heat stress. Overall, our results suggest that the algal symbionts increase coral holobiont susceptibility to `elevated temperatures. Currently, we can only speculate whether coral species, such as E. paradivisa, with the plasticity to flourish also as apo-symbionts, may have a greater chance to withstand the upcoming global change challenge.