Molecular and cellular bases of coral symbiosis and its breakdown

interaction and is hypothesized to have given rise to much of eukaryotic cellular complexity. The endosymbiosis between corals and dinoflagellate algae is essential to the energetic requirements of coral-reef ecosystems. However, coral reefs are in danger due to elevated ocean temperatures and other stressors that lead to the breakdown of this symbiosis in a process called “coral bleaching”. Despite the importance of coral reefs, the molecular and cellular basis of how corals maintain a healthy endosymbiosis and avoid bleaching is poorly understood, partly because of the lack of tractable genetic model systems. My lab has focused on developing genetic tools in several symbiotic cnidarians to allow rigorous functional testing of candidate genes and pathways. One side of my lab uses the small anemone Aiptasia, which is symbiotic with similar algal strains to those found in reef-building corals, as an experimentally tractable model. Excitingly, we have recently developed reverse-genetic methods in Aiptasia, allowing us to test gene function for the first time. 
While we are progressing in understanding symbiosis and bleaching mechanisms in Aiptasia, we want to compare these mechanisms to ecologically important reef-building corals. To this end, we have successfully used the CRISPR/Cas9 technology to create genetic changes in the coral Acropora millepora. We have used this technique to functionally characterize genes that underlie coral heat tolerance and other ecologically important traits. However, the once-a-year access to zygotes dictated by natural spawning events limits our ability to rapidly study gene function in reef-building corals. To solve this issue, we have combined novel methods to spawn corals in the lab with our CRISPR/Cas9 methods to generate a genetically tractable coral model system. Using this approach, we can generate genetically modified coral lines to study mechanisms of symbiosis and bleaching throughout the year. Our long-term goal is to gain critical molecular insights into how corals can adapt to climate change. Finally, by comparing Aiptasia and corals, we also hope to gain insights into the evolution of endosymbiosis.

Speaker: Phillip Cleves, Carnegie Institution for Science