Genomic and Transcriptomic Analyses Illuminate the Molecular Basis of the Unique Lifestyle of a Tubeworm, Lamellibrachia Satsuma

Vestimentiferan tubeworms are representative members of deep-sea chemosynthetic ecosystems. In this study, we developed a draft genome and gene models and performed genomic and transcriptomic analyses of Lamellibrachia satsuma, the only vestimentiferan reported from the euphotic zone. The quality of the genome assembly and gene models is comparable to or higher than those of previously reported vestimentiferan tubeworms. Tissue-specific transcriptome sequencing revealed that Toll-like receptor genes and lineage-specific expanded bacteriolytic enzyme genes are highly expressed in the obturacular and vestimental regions, respectively, suggesting the importance of these tissues in defense against pathogens. On the other hand, globin subunit genes are expressed almost exclusively in the trunk region, supporting the hypothesis that the trophosome is the site of haemoglobin biosynthesis. Vestimentiferan-specific expanded gene families included chitinases, ion channels, and C-type lectins, suggesting the importance of these functions for vestimentiferans. C-type lectins in the trunk region, in particular, may be involved in recognition of pathogens, or in interactions between tubeworms and symbiotic bacteria. Our genomic and transcriptomic analyses enhance understanding of molecular mechanisms underlying the unique lifestyle of vestimentiferan tubeworms, particularly their obligate mutualism with chemosynthetic bacteria.