Project description: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. In order to elucidate the transcriptomic response of the coral host in the presence of its associated symbiont, we utilized a comparative framework. Post-metamorphic aposymbiotic coral polyps of Orbicella faveolata were compared to symbiotic coral polyps 9 days after metamorphosis 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 pathways turned 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.
Project description:We subjected three inshore and four offshore genotypes of the coral Orbicella faveolata to 30, 31, 32, or 33ºC for 31 days and measured photochemical efficiency (Fv/Fm), the types and relative abundance of dinoflagellate endosymbionts, and gene expression of the host and symbiont. All inshore coral genotypes, regardless of symbiont type, were significantly more thermotolerant than offshore genotypes based on declines in Fv/Fm. The most heat-tolerant inshore genotype (In1) was dominated by Durusdinium trenchii; all other genotypes were Breviolum-dominated, suggesting local adaptation or acclimatization contributes to the heat tolerance of inshore genotypes. After 31 days of heat stress, all coral genotypes (except In2) had lost most of their Breviolum and became dominated by D. trenchii. Host genotype In1 presented unique expression patterns of genes involved in heat shock response, immunity, and protein degradation. There were few changes in the symbiont transcriptomes of inshore corals under heat stress, but significant changes in symbiont gene expression from the offshore colonies, including increases in ribosomal and photosynthetic proteins. These data show that the differential thermotolerance between inshore and offshore O. faveolata in the Florida Keys is associated with statistically significant differences in both host and symbiont gene expression that provide insights into the mechanisms underlying holobiont heat tolerance.
