Investigating the roles of transforming growth factor-beta in immune response of Orbicella faveolata, a scleractinian coral

Symbiotic relationships range from parasitic to mutualistic, yet all endosymbionts face similar challenges, including evasion of host immunity. Many symbiotic organisms have evolved similar mechanisms to face these challenges, including manipulation of the host's transforming growth factor-beta (TGF beta) pathway. Here we investigate the TGF beta pathway in scelaractinian corals which are dependent on symbioses with dinoflagellates from the family Symbiodiniaceae. Using the Caribbean coral, Orbicella faveolata, we explore the effects of enhancement and inhibition of the TGF beta pathway on host gene expression. Following transcriptomic analyses, we demonstrated limited effects of pathway manipulation in absence of immune stimulation. However, manipulation of the TGF beta pathway significantly affects the subsequent ability of host corals to mount an immune response. Enhancement of the TGF beta pathway eliminates transcriptomic signatures of host coral immune response, while inhibition of the pathway maintains the response. This is, to our knowledge, the first evidence of an immunomodulatory role for TGF beta in a scelaractinian coral. These findings suggest variation in TGF beta signaling may have implications in the face of increasing disease prevelance. Our results suggest that the TGF beta pathway can modulate tradeoffs between symbiosis and immunity. Further study of links between symbiosis, TGF beta, and immunity is needed to better understand the ecological implications of these findings.