The hard-shelled mussel (Mytilus coruscus) is an economically important shellfish that has been cultivated for the last decade. Due to over-exploitation, most mussel stocks have dramatically declined. Efforts to study this species' natural distribution, genetics, breeding, and cultivation have been hindered by the lack of a high-quality reference genome. To address this, we produced a hybrid high-quality reference genome of M. coruscus using a long-read platform to assemble the genome and short-read, high-quality technology to accurately correct for sequence errors. The genome was assembled into 10,484 scaffolds, a total length of 1.90 Gb, and a scaffold N50 of 898 kb. Ab initio annotation of the M. coruscus genome assembly identified a total of 42,684 genes. This accurate reference genome of M. coruscus provides an essential resource with the advantage of enabling the genome-scale selective breeding of M. coruscus. More importantly, it will also help in deciphering the speciation and local adaptation of the Mytilus species.

BackgroundScylla paramamosain (Crustacea: Decapoda: Portunidae: Syclla De Hann) is a commercially important mud crab distributed along the coast of southern China and other Indo-Pacific countries (Lin Z, Hao M, Zhu D, et al, Comp Biochem Physiol B Biochem Mol Biol 208-209:29–37, 2017; Walton ME, Vay LL, Lebata JH, et al, Estuar Coast Shelf Sci 66(3–4):493–500, 2006; Wang Z, Sun B, Zhu F, Fish Shellfish Immunol 67:612–9, 2017). While S. paramamosain is a euryhaline species, a sudden drop in salinity induces a negative impact on growth, molting, and reproduction, and may even cause death. The mechanism of osmotic regulation of marine crustaceans has been recently under investigation. However, the mechanism of adapting to a sudden drop in salinity has not been reported.MethodsIn this study, transcriptomics analysis was conducted on the gills of S. paramamosain to test its adaptive capabilities over 120 h with a sudden drop in salinity from 23 ‰ to 3 ‰.ResultsAt the level of transcription, 135 DEGs (108 up-regulated and 27 down-regulated) annotated by NCBI non-redundant (nr) protein database were screened. GO analysis showed that the catalytic activity category showed the most participating genes in the 24 s-tier GO terms, indicating that intracellular metabolic activities in S. paramamosain were enhanced. Of the 164 mapped KEGG pathways, seven of the top 20 pathways were closely related to regulation of the Na+ / K+ -ATPase. Seven additional amino acid metabolism-related pathways were also found, along with other important signaling pathways.ConclusionIon transport and amino acid metabolism were key factors in regulating the salinity adaptation of S. paramamosain in addition to several important signaling pathways.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4803-x) contains supplementary material, which is available to authorized users.

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BackgroundThe mud crab (Scylla paramamosain) is a euryhaline and commercially important species. MiRNAs participate in the regulation of many physiological activities.ResultsThe miRNA transcriptome of the gills of S. paramamosain was used to investigate the expression profiles of miRNAs in response to a sudden drop in salinity. In total, seven known miRNAs and 43 novel miRNAs were identified, with 18 differentially expressed small RNAs. Fourteen thousand nine hundred fifty-one differentially expressed miRNAs target genes were screened by prediction. GO analysis of differentially expressed miRNAs target genes indicated that 578 genes associated with cellular processes, 523 associated with metabolic processes, and 422 associated with single-organism processes were the most strongly affected by a sudden drop in salinity from 23‰ to 3‰. KEGG pathway analysis showed 14 pathways were related to amino acid metabolism, which plays an important role in osmoregulation. Besides, several pathways were associated with starch and sucrose metabolism (ko00500), glycosaminoglycan degradation (ko00531), and galactose metabolism (ko00052).ConclusionsS. paramamosain regulated osmotic pressure and energy balance by regulating target genes to adapt to a sudden changes in salinity. These results provided a basis for further investigations of miRNA-modulating networks underlying the osmoregulation of S. paramamosain.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4981-6) contains supplementary material, which is available to authorized users.

Scylla paramamosain is a commercially important species distributed along the coast of southern China and other Indo-Pacific countries. Sudden salinity drop exceeding the adjustment capability of S. paramamosain can result in damage or even mortality. In our previous study, we had analyzed the mechanism of adapting sudden drop in salinity from the level of transcriptomics and proteomics, respectively. This study performed a correlation analysis of RNA sequencing transcriptomics and iTRAQ proteomics in order to investigate the adaptation mechanisms to sudden salinity drop from 23‰ to 3‰. There were 3954 correlations and a total of 15 correlations for differentially expressed proteins (DEPs) and differentially expressed genes (DEGs) from proteomics and transcriptomics. The correlation between DEPs and DEGs was 0, and the Spearman correlation coefficient of the same trend correlation for DEPs and DEGs was the highest, reaching 0.9080. KEGG pathway enrichment correlation revealed that protein digestion and absorption (Ko04974), proximal tubule bicarbonate (Ko04964), and bile secretion (Ko04976) played important roles in Na+/H+ and Na+/K+ exchange. In addition, important genes related to osmoregulation, such as ion transport and carbonic anhydrase, were also detected in the correlation analysis for same trend DEPs_DEGs. In conclusion, the proteome and transcriptome correlation results from this study indicate that ion transport plays a critical role in the adaptation of S. paramamosain to sudden reduction in salinity.