Molecular biomineralization of octocoral skeletons: calcite versus aragonite (MINORCA)
Palaeontology
Final Report Abstract
Corals constitute a group of benthic aquatic organisms belonging to the phylum Cnidaria distributed worldwide. Taxonomically, corals are found in the subclass Octocorallia and the order Scleratinia - both belonging to class Anthozoa -, and in the class Hydrozoa. Common feature of coral species is the presence of a mineral skeleton composed of calcium carbonate (CaCO3). Coral skeletons play a very important ecological role as they represent the building blocks of coral reefs, one of the most biologically diverse ecosystems of the planet. Despite this, several aspects of coral biomineralization - the process by which corals deposit their skeletons - remain poorly understood. One knowledge gap revolves around the ability of corals of depositing skeletons formed by different CaCO3 polymorphs. Scleractinian corals produce skeletons composed of aragonite, while in the subclass Octocorallia both aragonite and calcite are observed. Although the exact mechanisms behind such diversity are unknown, previous studies have pointed to an interplay between biological and environmental factors. However, the vast majority of research has been conducted on scleractinians and information for octocorals is extremely limited. However, the presence of both CaCO3 polymorph within Octocorallia makes this group an ideal candidate to research skeleton polymorphism in corals. In this light, project MINORCA has contributed to our understanding of polymorphism diversity among coral skeletons, by investigating the mechanisms behind aragonite and calcite formation in octocorals. The project combined transcriptomic and proteomics to identify and compare the biomineralization toolkit (i.e., the genes used by corals to regulate biomineralization) among species with different skeleton compositions. The results included the first characterization of octocoral biomineralization toolkits, the sets of proteins secreted by corals into the skeleton to regulate calcification. In addition to identifying multiple new candidate genes, which represent potential targets for follow up studies - the comparison of toolkits - between aragonitic and calcitic octocorals revealed an extremely low degree of similarity, suggesting that different proteins are associated with the precipitation of different polymorphs. At the same time, this data revealed how octocorals (both aragonitic and calcitic) appear to have independently recruited proteins homologous to those previously associated with biomineralization in Scleractinia. To test and compare the effects of environmental variables on skeleton polymorphism, the aragonitic octocoral H. coerulea and the scleractinian M. digitata were exposed to different seawater molar ratios of magnesium and calcium (mMg:mCa). This parameter is among the main drivers of selective precipitation of calcite and aragonite and has been previously shown to promote the incorporation of calcite into scleractinian skeletons. Although calcite formation in M. digitata was also observed in this study, H. coerulea maintained aragonite precipitation throughout the experiments. Although the exact mechanisms behind such differences remain unclear, results of molecular analyses point to the regulation of calcium transport possibly playing a role.
Publications
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(2019) New Non-Bilaterian Transcriptomes Provide Novel Insights into the Evolution of Coral Skeletomes, Genome Biology and Evolution, 11(11): 3068–3081
Conci N., Wörheide G., Vargas S
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(2020) Comparative Proteomics of Octocoral and Scleractinian Skeletomes and the Evolution of Coral Calcification, Genome Biology and Evolution, 12(9):623–1635
Conci N., Lehmann M., Vargas S., Wörheide G.
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(2020). Molecular biomineralization of octocoral skeletons: calcite versus aragonite (Doctoral dissertation, lmu)
Conci, N.
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(2020). Resilience to climate change in an octocoral involves the transcriptional decoupling of the calcification and stress response toolkits
Vargas, S., Zimmer, T., Conci, N., Lehmann, M., & Wörheide, G.
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(2021) The biology and evolution of Calcite and Aragonite Mineralization in Octocorallia. Frontiers in Ecology and Evolution 9: 623774
Conci N., Vargas S., Wörheide G.
