Comparative Gene Analysis and Prediction of Innate Immunity and Apoptosis Machinery in Hydrothermal Vent Tubeworms

Siboglinid tubeworms are an emerging model system for symbiosis in extreme conditions. At deep-sea hydrothermal vents in the Pacific Ocean, they harbor a chemoautotrophic symbiont in a specialized organ, the trophosome, where the bacteria carry out primary production via oxidation of reduced sulfur compounds. The trophosome of siboglinid worms is suggested to be tightly regulated, symbiont-responsive, and developmentally homeostatic. The purported mechanism involves a cellular proliferative or apoptotic response to bacterial signals, environmental cues, or nutrition. Though these processes are well understood in more amenable model systems, there has been little work uncovering the tubeworm’s genetic potential for sensing and responding to symbiotic stimuli by canonical means, including pattern recognition receptors, innate immune effectors, and apoptotic regulators. In the present work, bioinformatics methods are employed to identify homologs to known regulatory genes, within two siboglinid tubeworms, Ridgeia piscesae, and Riftia pachyptila. Homologs found in EST libraries from each worm are characterized and evaluated for functional relevance to symbiosis by protein prediction, domain matching, and phylogenetic reconstruction. The major protein families here observed are the peptidoglycan recognition proteins (PGRPs) and the Caspases, accompanied by an overview of the worm’s potential apoptotic suite of genes. The siboglinid set of potential PGRPs presents similar characteristics to non-hydrothermal vent-associated symbiotic organisms. As well, the siboglinid apoptosis network is neither enriched nor reduced for any core components. The caspase gene family includes two major groups, and overall resembles the structural assortment recently seen in most non-derived apoptosis networks, but may present properties unique among annelids. The results of these analyses provide a suite of potential symbiosis-related genes for future investigations