Transcriptome assembly of Modiolus modiolus and comparative analysis with Bathymodiolus platifrons

Abstract

The genetic basis for bivalves' adaptation and evolution is not well understood. Even few studies have focused on the mechanism of molluscan molecular evolution between the coastal intertidal zone and deep-sea environment. In our studies, we first conducted the transcritpome assembly of Modiolus modiolus mussels living in coastal intertidal zones. Also, we conducted transcriptome comparison analyses between M. modiolus and Bathymodiolus platifrons living in hydrothermal vents and cold methane/sulfide-hydrocarbon seeps. De novo assemblies of the clean reads yielded a total of 182 476 and 156 261 transcripts with N50 values of 1 769 and 1 545 in M. modiolus and B. platifrons. A total of 27 868 and 23 588 unigenes were identified, which also displayed the similar GO representation patterns. Among the 10 245 pairs of putative orthologs, we identified 26 protein-coding genes under strong positive selection (Ka/Ks>1) and 12 genes showing moderate positive selection (0.5<Ka/Ks<1). Most of those genes are predicted to be involved in stress resistance. Overall, our study first provides the transcriptomic database for M. modiolus. Transcriptome comparison illustrates the genome evolution between M. modiolus and B. platifrons, and provides an important foundation for future studies on these two species.