Differential Regulation by Heat Stress of Novel Cytochrome P450 Genes from the Dinoflagellate Symbionts of Reef-Building Corals

Abstract

Exposure to heat stress has been recognized as one of the major factors leading to the breakdown of the coral-alga symbiosis and coral bleaching. Here, we describe the presence of three new cytochrome P450 (CYP) genes from the reef-building coral endosymbiont Symbiodinium (type C3) and changes in their expression during exposure to severe and moderate heat stress conditions. Sequence analysis of the CYP C-terminal region and two conserved domains, the "PERF" and "heme-binding" domains, confirmed the separate identities of the CYP genes analyzed. In order to explore the effects of different heat stress scenarios, samples of the scleractinian coral Acropora millepora were exposed to elevated temperatures incrementally over an 18-h period (rapid thermal stress) and over a 120-h period (gradual thermal stress). After 18 h of gradual heating and incubation at 26°C, the Symbiodinium CYP mRNA pool was approximately 30% larger, while a further 6°C increase to a temperature above the average sea temperature (29°C after 72 h) resulted in a 2-to 4-fold increase in CYP expression. Both rapid heat stress and gradual heat stress at 32°C resulted in 50% to 90% decreases in CYP gene transcript abundance. Consequently, the initial upregulation of expression of CYP genes at moderately elevated temperatures (26°C and 29°C) was followed by a decrease in expression under the greater thermal stress conditions at 32°C. These findings indicate that in the coral-alga symbiosis under heat stress conditions there is production of chemical stressors and/or transcriptional factors that regulate the expression of genes, such as the genes encoding cytochrome P450 monooxygenases, that are involved in the first line of an organism's chemical defense.

Host and Symbionts in Pocillopora damicornis Larvae Display Different Transcriptomic Responses to Ocean Acidification and Warming

“…Parsing out the symbiont-specific gene expression response is important in the effort to accurately predict effects of global ocean change on coral-dinoflagellate symbioses, as Symbiodinium and other dinoflagellates can display muted or dramatic responses in gene expression to elevated temperature and other stressors (Rosic et al, 2010(Rosic et al, , 2011Guo and Ki, 2012). Our results-greater expression changes in Symbiodinium vs. host-agree with a recent study in Papua New Guinea using adult A. millepora (Kenkel et al, 2017).…”

Mycosporine-Like Amino Acids from Coral Dinoflagellates

“…In the Caribbean coral Montastraea faveolata and their embryos, thermal stress resulted in gene expression changes altering cytoskeleton structure, decreasing the calcification rate, negatively affecting Ca ϩ2 homeostasis, and initiating cell death processes, such as apoptosis and necrosis (24,107). In transcriptomics of coral endosymbionts, differential regulation by heat stress was reported for newly discovered cytochrome P450 genes (80) and then for HSP70 and HSP90 (79,81), bringing new insights into the mechanisms of stress response. In corals exposed to environmental stressors, oxidative stress and the production of ROS such as superoxide and singlet oxygen, can damage proteins, lipids, and other cellular constituents (55), possibly resulting in the exclusion of the coral endosymbionts from the host tissues (38).…”

Site-specific variation in gene expression from Symbiodinium spp. associated with offshore and inshore Porites astreoides in the lower Florida Keys is lost with bleaching and disease stress

“…Gene expression analysis is a powerful tool increasingly utilized to determine responses of closely related coral and symbiotic zooxanthellae populations to stress [35,36,43,45]. Coral host populations of P .…”

“…PCP is involved in the capture of solar energy [33] and psaE stabilizes interactions within the photosystem 1 complex [34]. Variation in the expression of these metabolic genes affords functional variability to zooxanthellae and can be involved in acclimatization to bleaching and disease conditions [35–37]. …”