Gene expression of settled and metamorphosed Orbicella faveolata during establishment of symbiosis

Corals rely on a symbiosis with dinoflagellate algae (Symbiodinium spp.) to thrive in nutrient poor tropical oceans. However, the coral-algal symbiosis can break down during bleaching events, potentially leading to coral death. While genome-wide expression studies have shown the genes associated with the breakdown of this partnership, the full conglomerate of genes responsible for the establishment and maintenance of a healthy symbiosis remains unknown. Results from previous studies suggested little transcriptomic change associated with the establishment of symbiosis. We examined the transcriptomic response of the coral Orbicella faveolata in the presence (symbiotic) and absence (aposymbiotic) of Symbiodinium minutum, one of its associated symbionts. 9 days post-metamorphic aposymbiotic coral polyps of O. faveolata were compared to symbiotic coral polyps and the subsequent differential gene expression between control and treatment was quantified using cDNA microarray technology. Coral polyps exhibited differential expression of genes associated with nutrient metabolism and development, providing insight into control of pathways as a result of symbiosis driving early polyp growth. Furthermore, genes associated with lysosomal fusion were also upregulated, suggesting host regulation of symbiont densities soon after infection.