Transcriptional response of the heat shock gene hsp70 aligns with differences in stress susceptibility of shallow-water corals from the Mediterranean Sea

Abstract

Shallow-water corals of the Mediterranean Sea are facing a d ramatic increase in water temperature due to climate change, predicted to increase the frequency of bleaching and mass mortality events. However, supposedly not all corals are affected equally, as Lhey show differences in s1ress susceptibility, as suggested by phy• siological outputs of corals along temperature gradients and under controlled conditions in terrns of reproduction, demography, growth, calcification, and photosynthetic efficiency. In this study, gene expression and induction of a 70-kDa heat shock protein (HSP70) was analyzed in five cornmon shallow-water hard corals in the Mediterranean Sea, nan1ely Ascroides calycularis, Balmtophyllia europaea, CaryophyUia inomata, Cladocora caespitosa, and leptopsanunia provoli The main ain1 was to assess the contribution of this evolutionary conserved cytoprotective mechanism to the physiological plasticity of these species that possess different growth modes (solitary vs colonial) and trophic strategies (zooxanthellate vs azooxanthellate). Using quantitative real-ti me PCR, in siru hsp70 baseline levels and expression profiles after a heat-shock exposure were assessed. Levels of hsp70 and heat stress in.duction were higher in zooxanthellate than in azooxanthellate species, and different heat stress transcriptional profiles were observed between colonial and solitary zooxanthellate corals. On the whole, the hsp70 transcriptional response to heat stress aligns with stress susceptibility of the species and suggesrs a contribution of trophic stra1egy and morphology in shaping coral resilience ro stress. Understanding these molecular processes may contribute to assess the potential effects and relative resilience of Mediterranean cora ls under climate change. Marine ecosystems are declining worldwide d ue to global climate change and other anthropogenic impacts (Hughes et al., 2018). These rapid changes alter the structure of habitats and communities and cause the loss of many species. Of particular concern is the decline of scleractinian corals triggered by thermal stress (Hoegh-Guldberg et al" 2007). Rising sea surface temperature is linked to coral bleaching and mass mortality events in both symbiotic and non-symbiotic corals in the tropics and in the Mediterra nean Sea (Altieri et al., 2017; Jimenez et al., 20ll6; Rodolfo-Metalpa et al" 2006b). The Mediterranean Sea is warming a t two to three times the rate for the global ocean (Vargas• Yanez et al" 2008), showing an in creased occurrence of hot extremes by 200-500% throughout the region (Diffenbaugh et al., 2007). This is d ue to i ts position in the transition between the arid clim ate of North Africa and the temperate climate of central Europe, which renders Medi• terranean climate vulnerable to even relatively moderate modifications of the general circulation (Giorgi and Lionello, 2008). Furthermore, its

Divergent expression of hypoxia response systems under deoxygenation in reef‐forming corals aligns with bleaching susceptibility

“…Overall, our finding of higher expression of both hsp90 and hsp70 is consistent with previous reports of higher expression of these genes in stress-tolerant corals (Franzellitti et al, 2018;Poli et al, 2017;Seveso et al, 2018). Most importantly, A. tenuis demonstrated a greater ability to upregulate and downregulate HIFα implying a more finely tuned regulation of the HIF system, which facilitates a more rapid adjustment to the low oxygen environment, and a response consistent in hypoxia tolerance in other metazoans where HIF stress responses become suppressed during prolonged hypoxia exposure, for example, in high altitudes (Peng et al, 2017).…”

Simulating Bleaching: Long-Term Adaptation to the Dark Reveals Phenotypic Plasticity of the Mediterranean Sea Coral Oculina patagonica

“…HSP70 is a well establish stress-induced gene (Maor-Landaw et al, 2014). The underexpression of HSP70 in the bleached O. patagonica is similar to their representative expression in Mediterranean azooxanthellate corals compare to zooxanthellate corals (Franzellitti et al, 2018). However, underexpression of HSP70 may cause future difficulties to the coral if other stressors appear, such as a thermo-shock due to an extensive increase in seawater temperature (Gong, 2005).…”

Accelerated evolution at chaperone promoters among Antarctic notothenioid fishes

“…Environments characterized by frequent or chronic stress can select for the constitutive frontloading of gene families that are classically stress-inducible [19–34]. In systems for which constitutive expression of inducible genes is evolved, rather than plastic, it is not yet understood how natural selection has acted upon gene regulatory mechanisms to derive constitutive states.…”

“…In ectotherms for example, increases in the basal expression of stress-inducible genes that confer a derived, constitutive function are evident in many cases of physiological adaptation to environmental limits. These “frontloaded” genes are often hampered in their capacity for induction and arise among intraspecific groups occupying novel environments [18–29] or among interspecific groups [30–34]. The evolutionary mechanisms that drive inducible genes toward constitutive states are also important in understanding oncogenesis [35–37], pathogen resistance to drugs [38–40], and the evolution of functional morphology [41, 42].…”