Coral Thermal Tolerance: Tuning Gene Expression to Resist Thermal Stress

Abstract

The acclimatization capacity of corals is a critical consideration in the persistence of coral reefs under stresses imposed by global climate change. The stress history of corals plays a role in subsequent response to heat stress, but the transcriptomic changes associated with these plastic changes have not been previously explored. In order to identify host transcriptomic changes associated with acquired thermal tolerance in the scleractinian coral Acropora millepora, corals preconditioned to a sub-lethal temperature of 3°C below bleaching threshold temperature were compared to both non-preconditioned corals and untreated controls using a cDNA microarray platform. After eight days of hyperthermal challenge, conditions under which non-preconditioned corals bleached and preconditioned corals (thermal-tolerant) maintained Symbiodinium density, a clear differentiation in the transcriptional profiles was revealed among the condition examined. Among these changes, nine differentially expressed genes separated preconditioned corals from non-preconditioned corals, with 42 genes differentially expressed between control and preconditioned treatments, and 70 genes between non-preconditioned corals and controls. Differentially expressed genes included components of an apoptotic signaling cascade, which suggest the inhibition of apoptosis in preconditioned corals. Additionally, lectins and genes involved in response to oxidative stress were also detected. One dominant pattern was the apparent tuning of gene expression observed between preconditioned and non-preconditioned treatments; that is, differences in expression magnitude were more apparent than differences in the identity of genes differentially expressed. Our work revealed a transcriptomic signature underlying the tolerance associated with coral thermal history, and suggests that understanding the molecular mechanisms behind physiological acclimatization would be critical for the modeling of reefs in impending climate change scenarios.

Mechanisms of Thermal Tolerance in Reef-Building Corals across a Fine-Grained Environmental Mosaic: Lessons from Ofu, American Samoa

“…For example, Middlebrook et al (2008) showed that gains in thermal tolerance in A. aspera can occur in as little as 48 h of preconditioning. A similar response was observed in A. millepora following 8 days of experimental preconditioning to sub-bleaching temperatures (Bellantuono et al, 2012a). That corals can increase their thermal tolerance this quickly suggests that short term acclimation may be a key mechanism for resilience in the face of warming waters.…”

“…Short-term acclimation is attained through reduced expression of stress response genes under acute heat stress (Bay and Palumbi, 2015), whereas long-term acclimatization involves a shift in baseline expression under control conditions, referred to as "frontloading" (Barshis et al, 2013;Palumbi et al, 2014). The dampening of stress response genes following short-term preconditioning has also been reported in studies on A. millepora from the Great Barrier Reef, which showed a lesser magnitude response of genes associated with apoptotic signaling to acute heat stress following 10 days of preconditioning (Bellantuono et al, 2012a). Moreover, Gates and Edmunds (1999) showed that exposure to heat stress triggers upregulation of heat shock proteins in Montastrea franksi but a return to normal expression at 12 h despite continued exposure to heat stress, indicative of acclimatization to elevated temperatures.…”

Coral transcriptome and bacterial community profiles reveal distinct Yellow Band Disease states inOrbicella faveolata

“…16S ribosomal RNA gene microarrays, known as 'PhyloChips', provide a culture independent method to monitor relative abundance of a set of bacterial taxa under different conditions (Brodie et al, 2006), and have been extensively used in different biological systems (Wu et al, 2010;Mendes et al, 2011), including corals Kellogg et al, 2012;Roder et al, 2014). Coral transcriptome profiling has been used to examine differential gene expression under multiple physiological and developmental conditions (DeSalvo et al, 2008;Voolstra et al, 2009a,b;Portune et al, 2010;Bellantuono et al, 2012;Kaniewska et al, 2012;Barshis et al, 2013). Herein we extend the use coral complimentary DNA (cDNA) microarrays to examine host response to disease.…”

Uncovering Spatio-Temporal and Treatment-Derived Differences in the Molecular Physiology of a Model Coral-Dinoflagellate Mutualism with Multivariate Statistical Approaches

“…Briefly, whole, unfragmented S. hystrix colonies from Houbihu were exposed to either the control (27 °C) or elevated temperature (30 °C) for 48 hr in the former, and RNAs, DNAs, and proteins were extracted from triplicate colonies housed within each of triplicate tanks at each of the two temperature treatments at each of four sampling times (6,12,24, and 48 hr; 18 samples/sampling time). A tank average was calculated across the three pseudo-replicates within the same tank sampled at each time, resulting in 24 data points that were analyzed by the MSA discussed below (n=3 biological replicates/sampling time/treatment x 4 sampling times x 2 temperature treatments).…”

“…In recent years, a concerted effort has been made to better understand the basic biology of reefbuilding corals [1][2][3][4], as well as their response to changing environments [5][6][7]; the latter topic is especially pertinent given the extent of the anthropogenic pressures currently facing the high biodiversity ecosystems constructed by these cnidarian-dinoflagellate (genus Symbiodinium) endosymbioses [8][9]. The impact of changing environments on corals is undoubtedly complex, and many species have been shown to acclimate to extreme abiotic regimes previously hypothesized to compromise the integrity of these calcium carbonate-accreting mutualisms.…”