Identifying Candidate PPOs in Corals: Is the melanin synthesis cascade more similar to humans or insects? Authors: Emily Van Buren, Ivan Erasmo Ponce, Laura D Mydlarz General abstract: Melanin deposition that creates tissue discoloration is a phenotypic trait of coral immunity that has studied during disease outbreaks on coral reefs. Regardless of its presence in various diseases, the melanin synthesis cascade in coral species has remained elusive. To further identify the melanin pathway in several coral species and the genes involved in melanin synthesis, we performed BLAST searches with available mammalian, Insecta, and other cnidarian species’ melanin synthesis KEGG pathways. We also compare the main prophenoloxidase (PPO) candidate enzymes involved in melanin synthesis; tyrosinase, catechol oxidase, and laccases on available genomes using STRING. Composition Profiler was utilized to identify the enrichment of specific amino acids in cnidarian PPO candidate enzymes. We also use transcriptomic and proteomic data sets from Eunicea Black Band (EBB) disease to investigate melanin cascade enzymes in a disease model. EBB is unique due to its highly melanized immune response and serves as a model coral for this pathway. Preliminary data suggests the melanin cascade is more similar to Hydra vulgaris (55%) and Homo sapiens (40%) than insect species such as Aedes aegypti (23%) and Drosophila melanogaster (18%). By elucidating the melanin cascade in corals, we can understand its function and role of the relevant PPO candidate enzymes during specific disease events.