Comparative transcriptomic analysis illuminates the host-symbiont interactions in the deep-sea mussel Bathymodiolus platifrons

Abstract

Bathymodiolus platifrons adapted the chemosynthetic ecosystems, both cold seeps and hydrothermal vents, by harbouring gill symbionts. To survive these extreme and volatile ecological niches, the host mussel must be able to strictly regulate the symbionts in response to the environmental fluctuations. However, despite the research efforts, the molecular mechanisms governing host-symbiont interaction in deep-sea mussels are still largely unknown. Here, using the model deep-sea mussel Bathymodiolus plantiforns, we profiled the transcriptomic dynamic of the mussel gill during the loss and re-contact with symbionts with RNA-seq technology. The analysis of DEGs between untreated and symbiont loss samples revealed that metabolic and cellular organizational changes in the gill were associated with increased ribosomal activities, ubiquitin-proteasome systems, and autophagy. Meanwhile, the DE immune genes suggest that the host recognizes and interacts with endosymbionts through the pattern recognizing receptors, especially the Toll-like receptors. In addition, the DEGs between symbionts treated and environmental bacteria treated samples shed light on the mechanism of symbiont recognition. The symbionts treatment not only partially reversed the transcriptomic changes caused by symbiont-loss, but also suppressed host immune system which might facilitate the symbionts’ entrance and survival in the host bacteriocytes. All together, these results suggest that the host-symbiont system in B. platifrons is tightly regulated but also with plasticity to fit environmental fluctuations.