A Comparative Genomics Exploration of Inter-partner Metabolic Signaling in the Coral-algal Symbiosis
Doctor of Philosophy (PhD)
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coral, symbiosis, insulin, symbiodiniaceae, durusdinium trenchii
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At the foundation of coral reef ecosystems is the symbiosis between the coral host and its microbial community, particularly its photoautotrophic algae from the family Symbiodiniaceae. As a symbiosis centered around nutritional exchange, determining the mechanisms involved in the maintenance of this cooperative exchange is central to understanding how it breaks down. As the nutritional transfer primarily consists of sugars, this work first focuses on the cnidarian insulin signaling pathway, an evolutionarily important metazoan pathway involved in diverse functions, most notably metabolism. This dissertation unveiled 360 putative cnidarian insulin-like peptides (cnILPs) from existing transcriptomic datasets, where they were previously missed due to the bioinformatic methods employed. Significantly, symbiotic corals and anemones possessed the greatest diversity in insulin-like peptides compared to other cnidarian taxa. Conserved transcriptional responses of the cnILPs were also detected, particularly cnILP-B down-regulation in response to symbiosis along with a non-specific cnILP up-regulation in response to thermal stress. These trends coincide well with known transcriptional responses of ILPs in diverse organisms ranging from the nematode C. elegans to humans, implicating for the first time that insulin signaling similarly functions in symbiosis and stress response in non-bilaterians. This dissertation also focused on the genome of the thermotolerant Durusdinium trenchii, which is well-known to confer thermotolerance on diverse coral species. We identified considerable duplication of gene blocks, more than 10-100x that of other Symbiodinaceae species, in support of previous hypotheses regarding a near or whole genome duplication event. Importantly, within these duplicated gene regions we detected extensive positive selection on genes central to the maintenance and repair of chloroplast structures like thylakoid membranes and photosystem II, a primary site of damage during photoinhibition. Widespread genome duplication and adaptive selection on photosynthetic functions is significant as it aligns with previous physiological studies identifying this as a factor in the thermotolerance of D. trenchii. This dissertation for the first time not only substantiates previous hypotheses of genome duplication in D. trenchii, but connects this duplication to the acquisition of thermotolerance in D. trenchii. Altogether, this dissertation highlights the importance for further investigations into the functions of the insulin signaling pathway in coral-algal symbioses and stress response, as well as confirms genomic duplication and selection as contributing to the evolutionary acquisition of thermotolerance in the symbiont D. trenchii.
Dougan, Katherine E., "A Comparative Genomics Exploration of Inter-partner Metabolic Signaling in the Coral-algal Symbiosis" (2020). FIU Electronic Theses and Dissertations. 4706.
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