Transcriptomic analyses of the responses of corals to environmental stress

Aguilar Hurtado, Catalina (2016) Transcriptomic analyses of the responses of corals to environmental stress. PhD thesis, James Cook University.

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Abstract

Coral reefs are the oceans' most diverse and productive ecosystems. However, reef ecosystems are also one of the most endangered habitats on Earth, due to their fragility and exposure to both abiotic and biotic stressors. Understanding the impacts that environmental stressors have on the coral cellular mechanisms is integral for determining the coral health status. It also has important implications for persistence of coral reefs under rapidly changing climatic conditions. In this PhD study, I implemented a transcriptomic approach to investigate the response of the coral A. millepora to biotic and abiotic challenges in an attempt to better understand the molecular mechanisms underlying specific and general coral stress responses.

In Chapter 2, I focus on the coral response to lipopolysaccharidae (LPS) challenge in order to better understand innate immunity in corals. By using differential gene expression analysis and comparative genomics, I provide evidence that the coral response to LPS challenge resembles that of vertebrates. In addition, the effect of pre-exposure to high pCO2 conditions on the response to LPS challenge was investigated where, as in vertebrates and Drosophila, hypercapnia impaired the innate immune response. The results obtained support the hypothesis that coral immunity is likely to be compromised by near-future ocean acidification conditions and that cumulative stressors may predispose corals to increased disease.

In Chapter 3, I investigate the molecular mechanisms underlying the coral response to hypo-osmotic stress, again through application of transcriptomic approaches. Previous studies on corals and other marine invertebrates have enabled identification of a group of genes that respond to a wide range of stressors, whereas distinct sets of genes respond to specific stressors. Results described in this chapter illustrate that common responses to environmental stressors in Acropora sp. include up-regulation of genes involved in macromolecular and oxidative damage, while up-regulation of genes involved in amino acid metabolism and transport represent specific responses to salinity stress. These results provide important insights into how corals respond at the molecular level to low salinity events, which are predicted to increase under future climate scenarios due to increased frequency of intense rainfall events.

In Chapter 4, I examine the production of dimethylsulphoniopropionate (DMSP) by corals under salinity stress, in order to better understand the biosynthetic pathway and the role this compound in the coral. The concentration of DMSP increased in the coral under hypo-saline conditions, contradicting the assumption that DMSP functions as an osmolyte in corals, as is the case in higher plants and algae. Results described in this chapter suggest that DMSP production primarily serves as an overflow mechanism for removal of excess methionine arising from catabolism of betaines, although DMSP may also serve as a scavenger of ROS. The transcriptomic analyses also enabled identification of candidate genes for roles in DMSP biosynthesis. When DMSP was produced in response to hyposaline stress, coral homologues of each of the four enzymes classes implicated in DMSP biosynthesis (aminotransferase, reductase, methyltransferase, and decarboxylase) were up-regulated, linking specific genes to production of this compound from methionine in corals.

In Chapter 5, the published data and that described in all of the previous thesis chapters are used in attempt to establish the general mechanisms used by corals to respond to environmental stress. The transcriptomic data generated here provide novel insights into conserved and specific molecular mechanisms used by corals under stress, and advances our understanding of how corals are likely to respond to the challenges of a changing marine ecosystem.

Item ID: 49678
Item Type: Thesis (PhD)
Keywords: abiotic challenges, Acropora millepora, biotic challenges, corals, environmental stressors, gene expression, global warming, immune responses, immunology, molecular genetics, molecular mechanisms, ocean acidification, ocean warming, salinity stress, stressors
Date Deposited: 25 Jul 2017 23:15
FoR Codes: 06 BIOLOGICAL SCIENCES > 0604 Genetics > 060405 Gene Expression (incl Microarray and other genome-wide approaches) @ 50%
06 BIOLOGICAL SCIENCES > 0699 Other Biological Sciences > 069902 Global Change Biology @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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