The enhanced expression of heat stress-related genes in scleractinian coral ‘Porites harrisoni’ during warm episodes as an intrinsic mechanism for adaptation in ‘the Persian Gulf’

Abstract

Shallow water tropical reefs are widely threatened by anthropogenic ocean warming which sometimes exceeds their thermal tolerance limit. The majority of reefs have been currently predicted to entirely disappear if CO2 emissions continue at the present rate. However, certain species are thermally resilient and can quickly adapt to anomalous thermal stress events by altering the expression of heat stress-related genes, known as gene expression plasticity. Here, we examined the expression of key genes (i.e., heat-shock proteins, oxidative stress, immune response, ion transport, apoptosis, anti-apoptosis) in the scleractinian submassive coral Porites harrisoni and cytochrome P450 gene of its algal symbionts collected from the northeastern Persian Gulf during warm (August) and cold (December) periods. The potential for recovery from severe heat stress in August was additionally examined through transplantation of partially bleached coral fragments from shallow (~ 2.5 m) to a deeper site (~ 9 m), close to colonies of the same species experiencing much less heat stress. To evaluate the acclimation capability, several healthy deep (~ 9 m) coral fragments were transplanted to the shallow (~ 2.5 m) site experiencing severe heat stress. A significant upregulation of heat-shock proteins in response to heat stress was found and identified as the primary defense mechanism against heat stress-induced bleaching. In conjunction with the apoptotic gene downregulation, the immune response gene in acclimation samples showed pronounced upregulation, indicating high compatibility of deep corals to thermal changes. In recovery samples, the expression of the studied genes was similar to the expression of samples that underwent much less heat stress, which implies they were fully recovered. The expression of the cytochrome P450 gene showed no significant changes in all experiments. Overall, the findings suggest that P. harrisoni in the Persian Gulf is a thermal-tolerant species compared with counterpart species elsewhere in the world and can be classified as a thermally resilient coral. Thus, transplanting P. harrisoni in warm regions, where native corals have been subjected to climate change-driven mortality, might maintain the coral community under enhanced global warming scenarios.