Genetic Variation in Response to Global Warming in a Coral Reef Species, Porites lobata

Climate change due to global warming is one of the worst environmental disasters in the world, which affects all ecosystems and has led to increasing degradation of coral reefs. The increase of sea surface temperature is inversely related to the resistance of corals and is directly associated with their bleaching. High temperature disrupts the symbiotic relationship between coral and algal symbiont and results in coral bleaching. To evaluate the adaptation of corals to heat stress, in this study, we investigated the thermal stress effect on the expression of genes involved in programmed cell death (PCD), cysteinyl aspartate proteases 3 (will be mentioned as Caspas3 hereafter) and anti-apoptotic pathway, B-cell lymphoma 2 (will be mentioned as Bcl2 hereafter) in Porites lobata (Dana, 1846). Corals were incubated at 25°C for 2 weeks (adaptation period) and then exposed to 34°C (heat shock) for 24 and 48 hours. Then, the expression of genes was measured using real-time PCR. The results revealed that both genes were up-regulated at 24 hours after heat induction. Bcl-2 expression (anti-apoptotic gene) was induced at 24 hours and was down-regulated at 48 hours. In contrast, Caspase3 (apoptotic gene) continued to be expressed up to 48 hours. These results might indicate that coral cells are headed towards bleaching and death with increased temperature. The results of this study, regarding the observed expression patterns, can clarify the response of different genes to a thermal stress in coral reefs. The exposure of corals to acute conditions with high temperatures presented the behavior of the desired genes in the studied conditions.