Project description:Abstract The coral–dinoflagellate symbiosis is increasingly disrupted by global and local anthropogenic stressors. Coral bleaching is primarily a result of high sea surface temperatures, while eutrophication is associated with reef ecosystem degradation. Excess inorganic nitrogen relative to phosphate has been proposed to directly sensitise corals to thermal bleaching and accelerate reef decline. We assessed the proteomic response of the dinoflagellate coral symbiont Symbiodinium microadriaticum to elevated temperatures under multiple nutrient conditions by mass spectrometry. Elevated temperatures resulted in reductions of many chloroplast proteins, particularly light-harvesting complexes, with simultaneous increases in chaperone proteins. N:P imbalance had a larger effect on the proteome than temperature, but the biological processes and proteins responding to each stressor largely overlapped. The proteomes were highly similar at low N:P ratios but were strongly affected by phosphate starvation. High N:P ratios inhibited cell division, reflected by changes in proteins involved in protein translation. Imbalanced N:P did not increase sensitivity to high temperatures as measured by physiological means; however, imbalanced N:P strongly upregulated cell redox homeostasis proteins at high temperatures. As redox balance is critical during thermal bleaching, these data provide insight into the mechanisms of cellular responses to thermal and multiple stresses in the coral–dinoflagellate symbiosis.
Project description:Using transcriptomics, we show that Symbiodinium acclimation to elevated temperature involves up-regulated expression of meiosis genes followed by up-regulated expression of numerous reactive oxygen species scavenging genes and molecular chaperone genes. Our study connects Symbiodinium transcriptional regulation with physiological heat stress responses as well as known bleaching responses of corals harboring these same Symbiodinium. By uncovering these critical links, we greatly advance understanding of the bleaching susceptibility of corals, which is a key process responsible for global coral reef health.
Project description:RNA editing is a rare post-transcriptional event that provides cells with an additional level of gene expression regulation. It has been implicated in various processes including adaptation, viral defence and RNA interference; however, its potential role as a mechanism in acclimatization has just recently been recognised. Here, we show that RNA editing occurs in 1.6% of all nuclear-encoded genes of Symbiodinium microadriaticum, a dinoflagellate symbiont of reef-building corals. All base-substitution edit types were present, and statistically significant motifs were associated with three edit types. Strikingly, a subset of genes exhibited condition-specific editing patterns in response to different stressors that resulted in significant increases of non-synonymous changes. We posit that this previously unrecognised mechanism extends this organism's capability to respond to stress beyond what is encoded by the genome. This in turn may provide further acclimatization capacity to these organisms, and by extension, their coral hosts.
