Gene regulation underpinning increased thermal tolerance in a laboratory‐evolved coral photosymbiont

Abstract

Small increases in ocean temperature can disrupt the obligate symbiosis between corals and dinoflagellate microalgae, resulting in coral bleaching. Little is known about the genes that drive the physiological and bleaching response of algal symbionts to elevated temperature. Moreover, many studies to‐date have compared highly divergent strains, making it challenging to accredit specific genes to contrasting traits. Here, we compare transcriptional responses at ambient (27°C) and bleaching‐relevant (31°C) temperatures in a monoclonal, wild‐type (WT) strain of Symbiodiniaceae to those of a selected‐strain (SS), derived from the same monoclonal culture and experimentally evolved to elevated temperature over 80 generations (2.5 years). Thousands of genes were differentially expressed at a log fold‐change of >8 between the WT and SS over a 35 days temperature treatment period. At 31°C, WT cells exhibited a temporally unstable transcriptomic response upregulating genes involved in the universal stress response such as molecular chaperoning, protein repair, protein degradation and DNA repair. Comparatively, SS cells exhibited a temporally stable transcriptomic response and downregulated many stress response genes that were upregulated by the WT. Among the most highly upregulated genes in the SS at 31°C were algal transcription factors and a gene probably of bacterial origin that encodes a type II secretion system protein, suggesting interactions with bacteria may contribute to the increased thermal tolerance of the SS. Genes and functional pathways conferring thermal tolerance in the SS could be targeted in future genetic engineering experiments designed to develop thermally resilient algal symbionts for use in coral restoration and conservation.

Different levels of energetic coupling between photosynthesis and respiration do not determine the occurrence of adaptive responses of Symbiodiniaceae to global warming

“…This suggests that neither a coupled nor an uncoupled phenotype provides an advantage in terms of defining the capacity of a given species to adapt to global warming. However, we cannot exclude the possibility that other responses have been developed in long‐term heat‐stressed cells (Chakravarti et al ., 2020). Ecologically, this lack of adaptive capabilities in Symbiodiniaceae confirms the susceptibility of coral reefs to ocean warming.…”

Shotgun Proteomics Identifies Active Metabolic Pathways in Bleached Coral Tissue and Intraskeletal Compartments

“…However, no heat shock proteins were identified at significant levels in this study. Few coral bleaching studies have reported the presence of the chaperone proteins detected in the current study (Bellantuono et al, 2012;Maor-Landaw et al, 2014;Chakravarti et al, 2020).…”

Environmental Concentrations of Herbicide Prometryn Render Stress-Tolerant Corals Susceptible to Ocean Warming

“…Interestingly, we also observed an upregulation of certain genes involved in ribosome function and protein digestion and absorption solely under heat stress conditions, suggesting their role in preventing the accumulation of damaged proteins. 65,66 However, the presence of herbicides impeded the regulatory capacity of these partially up-regulated genes, potentially hindering coral acclimatization to heat stress conditions. Moreover, co-stress on the 21st day was found to inhibit important pathways involved in phagosome and lysosome functions compared with heat stress alone (Figure 4a), implying impaired cellular functions in coral host cells.…”