Variation in antioxidant gene expression in the scleractinian coral Acropora millepora under laboratory thermal stress

Abstract

The effects of climate change over the last few decades have pushed the majority of reef-building corals close to their upper thermal limit. Upon exposure to thermal stress, the intracellular formation of harmful oxygen intermediates can lead to the disruption of the obligate symbiosis between the coral host and their dinoflagellate endosymbionts (zooxanthellae), a process known as coral bleaching. Applications of molecular techniques to cnidarian research have recently enhanced our understanding of the magnitude of corals' transcriptional response to various stressors. In the present study, we developed a quantitative real-time polymerase chain reaction assay to assess expression levels of 4 genes involved in the corals' oxidative stress response (HSP70, MnSOD, ferritin, Zn 2+ -metalloprotease) after exposure to laboratory-controlled thermal stress. Using the IndoPacific reef coral Acropora millepora, our study provides the first population-scale analysis of antioxidant gene expression in coral. Despite the significant up-regulation of those 4 genes in the thermally stressed samples relative to non-stressed samples, our results show that there is an enormous intraas well as inter-colony variation in transcript abundance at a particular point in time. We discuss the potential roles of ferritin and Zn 2+-metalloprotease in the break down of the intra-cellular Fe 2+ -homeostasis and in coral host cell detachment, respectively, during bleaching conditions. Our results emphasise the importance of measuring inter-individual variation to gain an insight into the population response to a common and increasingly encountered environmental stressor.

Responses to iron limitation in two colonies of Stylophora pistillata exposed to high temperature: Implications for coral bleaching

“…Shick and Dowse 1985). The nubbins were chosen to provide an adequate representation of any regional physiological differences within each colony (Csá szá r et al 2009). This study design is appropriate to assess the physiological responses of individual colonies to iron limitation but cannot fully represent the broader metabolic response in the coral population (Crawford and Oleksiak 2007), which may involve genotypic variation in the defensive responses in S. pistillata.…”

The effects of a variable temperature regime on the physiology of the reef-building coralSeriatopora hystrix: results from a laboratory-based reciprocal transplant

“…DeSalvo et al, 2008;Bay et al, 2009;Császár et al, 2009;Reyes-Bermudez et al, 2009;Voolstra et al, 2009;DeSalvo et al, 2010;Portune et al, 2010;Starcevic et al, 2010;Hoogenboom et al, 2011;Kenkel et al, 2011;Leggat et al, 2011;Levy et al, 2011), generating a wealth of potentially interesting findings with regard to the molecular capacity of corals to acclimate to changes they may face over the Site of origin (SO), temperature treatment (TT) and interaction effects were deemed statistically significant at P<0.05 and, in such cases, are denoted by a tick. Only response variables for which significant differences were detected have been included..…”

Mycosporine-Like Amino Acids from Coral Dinoflagellates

“…Also, a number of changes in gene expression profiles have been reported following the exposure of coral to elevated temperatures. Focusing on the host (Acropora millepora), a significant upregulation in the levels of transcripts of 4 antioxidant genes (heat shock protein 70 [HSP70], MnSOD, ferritin, and Zn 2ϩ -metalloprotease), including a huge intercolony variation in their gene expression profiles, was reported (20). 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).…”