Rapid acclimation of juvenile corals to CO₂‐mediated acidification by upregulation of heat shock protein and Bcl‐2 genes

Abstract

Corals play a key role in ocean ecosystems and carbonate balance, but their molecular response to ocean acidification remains unclear. The only previous whole-transcriptome study (Moya et al. Molecular Ecology, 2012; 21, 2440) documented extensive disruption of gene expression, particularly of genes encoding skeletal organic matrix proteins, in juvenile corals (Acropora millepora) after short-term (3 d) exposure to elevated pCO2 . In this study, whole-transcriptome analysis was used to compare the effects of such 'acute' (3 d) exposure to elevated pCO2 with a longer ('prolonged'; 9 d) period of exposure beginning immediately post-fertilization. Far fewer genes were differentially expressed under the 9-d treatment, and although the transcriptome data implied wholesale disruption of metabolism and calcification genes in the acute treatment experiment, expression of most genes was at control levels after prolonged treatment. There was little overlap between the genes responding to the acute and prolonged treatments, but heat shock proteins (HSPs) and heat shock factors (HSFs) were over-represented amongst the genes responding to both treatments. Amongst these was an HSP70 gene previously shown to be involved in acclimation to thermal stress in a field population of another acroporid coral. The most obvious feature of the molecular response in the 9-d treatment experiment was the upregulation of five distinct Bcl-2 family members, the majority predicted to be anti-apoptotic. This suggests that an important component of the longer term response to elevated CO2 is suppression of apoptosis. It therefore appears that juvenile A. millepora have the capacity to rapidly acclimate to elevated pCO2 , a process mediated by upregulation of specific HSPs and a suite of Bcl-2 family members.

Transcriptomic Resilience of the Montipora digitata Holobiont to Low pH

“…Compared to previous investigations (Kaniewska et al, 2012;Moya et al, 2012Moya et al, , 2015, our results suggest a mild gene expression response of the adult coral holobiont to a 3-days exposure to acidified water in terms of number of DEGs and log 2 -fold change. Still, the log 2 -fold changes we found in this study are comparable to those observed in the resilient coral Siderastrea siderea under laboratory-induced ocean acidification conditions (Davies et al, 2016).…”

“…Also, delayed establishment of symbiosis between coral larvae and Symbiodinium has been observed as result of exposure to similar low pH conditions (Anthony et al, 2008;Crawley et al, 2010). However, the impacts of exposing corals to low pH vary across species and life stages (Kaniewska et al, 2012;Moya et al, 2012Moya et al, , 2015Davies et al, 2016).…”

Rapid adaptive responses to climate change in corals

“…Recent developments in omics technologies have enabled greater insight into the molecular pathways associated with plastic phenotypic responses and, in some cases, identified key genes whose altered expression may contribute to buffering against adverse environmental conditions within a generation 22,23 and across multiple generations 24,25 . Epigenetics, a term originally coined by Waddington in 1940, was intended to explain the phenomenon of cellular differentiation in multicellular organisms from a single genome 26 .…”

“…Within a lifetime, some corals can modulate their gross colony growth form to optimize light environments for photosynthesizing endosymbionts 51 , physiologically acclimatize to elevated temperatures 22 , and show signs of acclimatization under pH stress 14,23 . These examples suggest that corals may retain phenotypic plasticity in their adult life stage, which can itself be a trait affected by the corals' environment 52 .…”

Effects of elevated pCO2 and feeding on net calcification and energy budget of the Mediterranean cold-water coral Madrepora oculata

“…An upregulation of genes involved in calcification and other key physiological functions as a rapid response to counteract changes in seawater carbonate chemistry have been proposed for tropical corals (Kaniewska et al, 2012;Moya et al, 2012Moya et al, , 2015 and recently for the CWC Desmophyllum dianthus (Carreiro-Silva et al, 2014). The use of lipid reserves might also help sustain calcification during short-term exposure to elevated pCO 2 (Hennige et al, 2014).…”