Establishment of a New Model Sea Anemone for Comparative Studies on Cnidarian-Algal Symbiosis.

Frequent coral bleaching has drawn attention to the mechanisms of coral dinoflagellate endosymbiosis. Owing to the difficulty of rearing corals in the laboratory, model symbiosis systems are desired. The sea anemone Exaiptasia diaphana , hosting clade B1 of the genus Breviolum , has long been studied as a model system; however, a single species is insufficient for comparative studies and thus provides only limited resources for symbiosis research, especially regarding the specificity of host-symbiont associations. We established a clonal strain of the sea anemone Anthopleura atodai , whose symbiont was identified as a novel subclade of Symbiodinium (clade A) using a novel feeding method. We also developed a method to efficiently bleach various sea anemone species using a quinoclamine-based herbicide. Bleached A. atodai polyps were vital and able to reproduce asexually, exhibiting no signs of harmful effects of the drug treatment. Pilot studies have suggested that host-symbiont specificity is influenced by multiple steps differently in A. atodai and E. diaphana . RNAseq analyses of A. atodai showed that multiple NPC2 genes were expressed in the symbiotic state, which have been suggested to function in the transport of sterols from symbionts to host cells. These results reveal the usefulness of A. atodai in comparative studies of cnidarian-algal symbiosis.