Comparison of the complete mitochondrial genome of Phyllophorus liuwutiensis (Echinodermata: Holothuroidea: Phyllophoridae) to that of other sea cucumbers.

Sea cucumber species are abundant (>1400 species) and widely distributed globally. mtDNA sequencing is frequently used to identify the phylogenetic and evolutionary relationships among species. However, there are no reports on the mitochondrial genome of Phyllophorus liuwutiensis. Here, we performed mtDNA sequencing of P. liuwutiensis to examine its phylogenetic relationships with other echinoderms. Its mitochondrial genome (15 969 bp) contains 37 coding genes, including 13 protein-coding genes, 22 tRNA genes and 2 rRNA genes. Except for one protein-coding gene (nad6) and five tRNA genes encoded on the negative strand, all other genes were encoded on the positive strand. The mitochondrial bases of P. liuwutiensis were composed of 29.55% T, 22.16% C, 35.64% A and 12.64% G. The putative control region was 703 bp in length. Seven overlapping regions (1-10 bp) were found. The noncoding region between the genes ranged from 1 to 130 bp in length. One putative control region has been found in the P. liuwutiensis mitogenome. All of the tRNA genes were predicted to fold into a cloverleaf structure. In addition, we compared the gene arrangements of six echinoderms, revealing that the gene order of P. liuwutiensis was a new arrangement.

A multi-omic analysis of orange-spotted grouper larvae infected with nervous necrosis virus identifies increased adhesion molecules and collagen synthesis in the persistent state.

Grouper (Epinephelus coioides) is an important commercial maricultural fish, which suffers from nervous necrosis virus (NNV) infection. The molecular mechanisms underlying the pathogenesis of the viral infection are not clear. In this study, we combined deep RNA sequencing and label-free mass spectrum for the first time to analyze the transcriptomic and proteomic profiles in infected/dead, infected/survival (persistent), and infection-free (control)orange-spotted groupers in the larval stage. Further analyses showed that the transcriptome and proteome changed dramatically among the three distinct groups, especially differentially-expressed genes in the infected/dead and infected/survival larvae enriched for pathways related to immune response. Notably, the overlapped genes between transcriptomes and proteomes identified that genes related to collagen synthesis and adhesion molecules were enhanced in the persistent (infected/survival) stage, which might contribute to suppressing the acute and lethal immune responses upon NNV infection. These transcriptomic and proteomic datasets enable the investigation of molecular mechanisms underlying NNV infection, thus may help further development of molecular breeding in marine fishery.

De novo assembly of a chromosome-level reference genome of red-spotted grouper (Epinephelus akaara) using nanopore sequencing and Hi-C.

The red-spotted grouper Epinephelus akaara (E. akaara) is one of the most economically important marine fish in China, Japan and South-East Asia and is a threatened species. The species is also considered a good model for studies of sex inversion, development, genetic diversity and immunity. Despite its importance, molecular resources for E. akaara remain limited and no reference genome has been published to date. In this study, we constructed a chromosome-level reference genome of E. akaara by taking advantage of long-read single-molecule sequencing and de novo assembly by Oxford Nanopore Technology (ONT) and Hi-C. A red-spotted grouper genome of 1.135 Gb was assembled from a total of 106.29 Gb polished Nanopore sequence (GridION, ONT), equivalent to 96-fold genome coverage. The assembled genome represents 96.8% completeness (BUSCO) with a contig N50 length of 5.25 Mb and a longest contig of 25.75 Mb. The contigs were clustered and ordered onto 24 pseudochromosomes covering approximately 95.55% of the genome assembly with Hi-C data, with a scaffold N50 length of 46.03 Mb. The genome contained 43.02% repeat sequences and 5,480 noncoding RNAs. Furthermore, combined with several RNA-seq data sets, 23,808 (99.5%) genes were functionally annotated from a total of 23,923 predicted protein-coding sequences. The high-quality chromosome-level reference genome of E. akaara was assembled for the first time and will be a valuable resource for molecular breeding and functional genomics studies of red-spotted grouper in the future.

Complete mitochondrial genome of Holothuria leucospilata (Holothuroidea, Holothuriidae) and phylogenetic analysis.

The complete Holothuria leucospilata mitochondrial genome was determined and analyzed in this work. It had a circular mapping molecular with a total length of 15,904 bp and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 putative control region. Phylogenetic analysis showed that H. leucospilata clustered together with Holothuria scabra and Holothuria forskali. The complete mitochondrial genome provided in this work would be used for elucidation of Holothuroidea conservation genetics and evolutionary relationships.

Characterization of the complete mitochondrial genome of a holothurians species: Holothuria hilla (Holothuroidea: Holothuriidae).

Mitochondrial genome sequence is a great potential method to both resolve disputed taxonomic issues and to infer phylogenetic relationships among holothurians. In this study, we present the complete mitochondrial genome of Holothuria hilla which was 15,744 bp in length, containing 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a putative control region. The gene content and arrangement were typical for Holothuroidea ground pattern. The overall base composition was 32.43% A, 27.20% T, 24.35% C and 16.02% G, showing a bias toward A + T (59.63%). The maximum-likelihood tree based on the concatenated 13 protein-coding genes revealed the phylogenetic relationships among the Holothuroidea species.

The complete mitochondrial genome sequence of Stichopus variegatus (Echinodermata: Holothuroidea) and phylogenetic studies of Echinodermata.

At present, there exist some confusing issues on the species classification and phylogeny in Echinodermata. In this study, we first determined and described the complete mitochondrial genome of Stichopus variegatus. The complete mitogenome sequence had a circular mapping molecular with the total length of 16,315 bp and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a putative control region. To further validate the newly determined sequences, phylogenetic trees involving all the Holothuroidea and other Echinodermata species available in GenBank Database were constructed. These results would be used for the species identification and further phylogenetic studies of Echinodermata.

The complete mitochondrial genome sequence of Acentrogobius sp. (Gobiiformes: Gobiidae) and phylogenetic studies of Gobiidae.

At present, few morphological descriptions are available for Acentrogobius species and there exist some confused issues on the species classification and phylogeny. In this study, we first determined and described the complete mitochondrial genome of Acentrogobius sp. The complete mitogenome sequence is 17 083 bp in length, containing 13 protein-coding genes, two rRNA genes, 22 tRNA genes, a putative control region (CR), and a light-strand replication origin (OL). The overall base composition is 28.9% A, 26.2% T, 28.5% C, and 16.4% G, with a slight AT bias (55.1%). To furthermore validate the new determined sequences, phylogenetic trees involving all the Gobiidae species available in GenBank database were constructed. These results are expected to provide useful molecular data for species identification and further phylogenetic studies of Gobiiformes.

Molecular characterization and functional analysis of Toll-like receptor 3 gene in orange-spotted grouper (Epinephelus coioides).

Toll-like receptor 3 (TLR3) plays an important role in activating innate immune responses during viral infection. In this report, TLR3 (EcTLR3) was characterized and analyzed for the first time in Epinephelus coioides. The full-length EcTLR3 cDNA is predicted to encode a 909 amino acid polypeptide that contains a signal peptide sequence, 18 leucine-rich repeat (LRR) motifs, a transmembrane region and a Toll/interleukin-1 receptor (TIR) domain. Quantitative real-time PCR revealed that the EcTLR3 mRNA was much more abundant in the liver than in other immune organs, and that the expression levels were very low in hemocyte and muscle. During development of the grouper, the levels of EcTLR3 transcripts increased with age, with very low expression levels at the early stages of development. EcTLR3 mRNA levels were examined in the liver at different times after treatment with polyriboinosinic polyribocytidylic acid (Poly I:C), and in nervous necrosis virus (NNV)-infected larval groupers. The results suggested that EcTLR3 plays an important role in a fish's defense against viral infection.