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RNA-Seq of S.pistillata samples exposed to a 6-months darkness

ABSTRACT: Telomere DNA length is a complex trait controlled both by multiple loci and environmental factors. Even though the use of telomere DNA length measurement, as a method of assessing stress accumulation and predicting how this will influence survival, is currently being studied in numerous human cohort studies, the importance of telomere length for stress response in ecological studies remains at its infancy. Here, we investigated the telomere changes occurring in the symbiotic coral Stylophora pistillata that has experienced a continuous darkness over 6 months. This stress condition led to the loss of its symbionts, as what is also observed when bleaching occurs in the field at a large-scale due to climate changes and anthropogenic activities, threatening the worldwide reef ecosystem. We found that the continuous darkness condition was associated to telomere DNA length shortening and a downregulation of the expression of the telomere-associated protein POT2. These results pave the way for future studies on the role of telomere in coral stress response and the importance of telomere dysregulation in endangered coral species

ORGANISM(S): Stylophora pistillata

PROVIDER: GSE171268 | GEO | 2021/09/20

REPOSITORIES: GEO

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Project description:Over the past several decades, corals worldwide have been affected by global warming, experiencing severe bleaching events that have often lead to coral death. The symbiotic Red Sea coral Stylophora pistillata is considered an opportunistic ‘r’ strategist, thriving in relatively unstable and unpredictable environments, and it is considered a stress-tolerant species. This study aimed to examine S. pistillata gene expression and to clarify the cellular pathways that are active during short-term heat stress caused by an increase from 24°C to 34°C over a 10-day period. Total RNA was extracted from heat-stressed coral fragments, labeled and hybridized against a designated S. pistillata custom microarray containing approximately 12,000 genes. Our results show that the heat stress reaction was sighted from 32°C and intensified significantly after 34°C treatment. Protein interaction networks of up- and down-regulated genes were constructed. The main clustering groups of up-regulated genes were ER stress and ER protein folding, cell cycle, ubiquitin-mediated proteolysis, cell death and cell death regulation and cellular stress response genes. These genes were enriched in cellular pathways related to the unfolded protein response (UPR) in the ER, ER-associated degradation (ERAD) and ubiquitin-mediated proteolysis. An analysis of the down-regulated genes yielded different clusters of genes related to extracellular matrix and actin organization, collagen, negative regulation of cell death and the Notch and Wnt signaling pathways. Genes encoding redox regulation proteins and molecular chaperones may be considered accurate “early warning genes”, while genes related to sensing and repairing DNA damage are severe heat-related genes. Here, we suggest that during short-term heat stress, S. pistillata might divert cellular energy into mechanisms such as UPR and ERAD at the expense of growth and biomineralization processes in an effort to recover from the stress.

Project description:Coral bleaching occurs in response to numerous abiotic stressors, the ecologically most relevant of which is hyperthermic stress due to increasing seawater temperatures. Bleaching events can span large geographic areas and are currently a potent threat to coral reefs worldwide. Much effort has been focused on understanding the molecular and cellular events underlying bleaching, and these studies have mainly utilized heat and light stress regimes. In an effort to determine whether different stressors share common bleaching mechanisms, we used cDNA microarrays for the corals Acropora palmata and Montastraea faveolata (containing > 10,000 features) to measure differential gene expression during darkness stress. This is the first coral microarray experiment aimed at darkness stress, and the first for these species to interrogate gene expression at such a large scale. Our results reveal a striking transcriptomic response to darkness in A. palmata involving chaperone and antioxidant up-regulation, growth arrest, and metabolic modifications. As these responses were also measured during thermal stress, our results suggest that different stressors may share common bleaching mechanisms. Furthermore, our results point to ER stress as a critical cellular event involved in darkness-specific (and possibly more general) molecular bleaching mechanisms. On the other hand, we identified a meager transcriptomic response to darkness in M. faveolata where gene expression differences between host colonies and/or sampling locations were greater than differences between control and stressed fragments. To this end, we discuss the importance of factors related to host genotype, Symbiodinium genotype, and the abiotic environment that influence host gene expression and thereby can hinder an investigator’s ability to measure gene expression during a condition of interest. We employed a reference design where all control and dark-stressed samples were compared to a pooled reference aRNA sample composed of aRNA from all fragments. Since all RNA samples were compared to the reference sample, direct comparisons of gene expression across all time points and conditions can be performed.

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RNA-Seq of S.pistillata samples exposed to a 6-months darkness

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