Gene expression profiles provide insights into the survival strategies in deep-sea mussel (Bathymodiolus platifrons) of different developmental stages

Background

Deep-sea mussels living in the cold seeps with enormous biomass act as the primary consumers. They are well adapted to the extreme environment where light is absent, and hydrogen sulfide, methane, and other hydrocarbon-rich fluid seepage occur. Despite previous studies on diversity, role, evolution, and symbiosis, the changing adaptation patterns during different developmental stages of the deep-sea mussels remain largely unknown.

Results

The deep-sea mussels (Bathymodiolus platifrons) of two developmental stages were collected from the cold seep during the ocean voyage. The gills, mantles, and adductor muscles of these mussels were used for the Illumina sequencing. A total of 135 Gb data were obtained, and subsequently, 46,376 unigenes were generated using de-novo assembly strategy. According to the gene expression analysis, amounts of genes were most actively expressed in the gills, especially genes involved in environmental information processing. Genes encoding Toll-like receptors and sulfate transporters were up-regulated in gills, indicating that the gill acts as both intermedium and protective screen in the deep-sea mussel. Lysosomal enzymes and solute carrier responsible for nutrients absorption were up-regulated in the older mussel, while genes related to toxin resistance and autophagy were up-regulated in the younger one, suggesting that the older mussel might be in a vigorous stage while the younger mussel was still paying efforts in survival and adaptation.

Conclusions

In general, our study suggested that the adaptation capacity might be formed gradually during the development of deep-sea mussels, in which the gill and the symbionts play essential roles.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08505-9.

Characterization of the IRF2 proteins isolated from the deep-sea mussel Bathymodiolus platifrons and the shallow-water mussel Modiolus modiolus

Interferon regulatory factors (IRFs) are transcription factors that play important roles in immune defense, stress response, hematopoietic differentiation, and cell apoptosis. IRFs of invertebrate organisms and their functions remain largely unexplored. In the present study, for the first time new IRFs (BpIRF2 and MmIRF2) were identified in the deep-sea mussel Bathymodiolus platifrons and the shallow-water mussel Modiolus modiolus. The open reading frame of BpIRF2 and MmIRF2 encoded putative proteins of 354 and 348 amino acids, respectively. Comparison and phylogenetic analysis revealed that both IRF2 proteins were new identified invertebrate IRF molecular. As transcriptional factors, both BpIRF2 and MmIRF2 could activate the interferon-stimulated response element-containing promoter and BpIRF2 could interact with itself. Moreover, both BpIRF2 and MmIRF2 were localized to the cytoplasm and nucleus. Collectively, these results demonstrated that IRF2 proteins might be crucial in the innate immunity of deep-sea and shallow-water mussels.