Transcriptional responses to low-salinity stress in the gills of adult female Portunus trituberculatus.

The swimming crab (Portunus trituberculatus, Portunus) can tolerate low salinity, but the mechanism of its varied salinity adaptation at the molecular level remains unclear. In this study, we prepared four mRNA and microRNA (miRNA) libraries using the gills collected from four salinity groups and performed RNA-sequencing (RNA-Seq) to identify the genes related to the low salinity. We set 25 ppt as the control group. A total of 659 genes were differentially expressed in at least one of the six comparison groups (25 ppt vs. 20 ppt, 25 ppt vs. 15 ppt, 25 ppt vs. 10 ppt, 20 ppt vs. 15 ppt, 20 ppt vs. 10 ppt and 15 ppt vs. 10 ppt). A total of 15 and 9 unigenes were downregulated and upregulated under low salinity compared with that in 25 ppt, respectively. Six genes, namely, aminopeptidase, centromere protein, cytochrome b5 reductase, bone morphogenetic protein, and two carbonic anhydrases, were selected for verification through quantitative real-time PCR. The results were consistent with the RNA-Seq results. Furthermore, 95 conserved miRNAs and 16 novel miRNAs were differentially expressed in at least one of the six comparison groups. Analysis of the miRNA-mRNA interaction showed that miR-2 and miR-317 regulated >50 mRNA targets. In addition, let-7c was downregulated in all groups under low salinity compared with that in the control group. This study helped elucidate the adaptation mechanism of the swimming crab in low-saline environments.