A draft genome assembly of the Chinese sillago (Sillago sinica), the first reference genome for Sillaginidae fishes.
ABSTRACT: Background:Sillaginidae, also known as smelt-whitings, is a family of benthic coastal marine fishes in the Indo-West Pacific that have high ecological and economic importance. Many Sillaginidae species, including the Chinese sillago (Sillago sinica), have been recently described in China, providing valuable material to analyze genetic diversification of the family Sillaginidae. Here, we constructed a reference genome for the Chinese sillago, with the aim to set up a platform for comparative analysis of all species in this family. Findings:Using the single-molecule real-time DNA sequencing platform Pacific Biosciences (PacBio) Sequel, we generated ?27.3 Gb genomic DNA sequences for the Chinese sillago. We reconstructed a genome assembly of 534 Mb using a strategy that takes advantage of complementary strengths of two genome assembly programs, Canu and FALCON. The genome size was consistent with the estimated genome size based on k-mer analysis. The assembled genome consisted of 802 contigs with a contig N50 length of 2.6 Mb. We annotated 22,122 protein-coding genes in the Chinese sillago genomes using a de novo method as well as RNA sequencing data and homologies to other teleosts. According to the phylogenetic analysis using protein-coding genes, the Chinese sillago is closely related to Larimichthys crocea and Dicentrarchus labrax and diverged from their ancestor around 69.5-82.6 million years ago. Conclusions:Using long reads generated with PacBio sequencing technology, we have built a draft genome assembly for the Chinese sillago, which is the first reference genome for Sillaginidae species. This genome assembly sets a stage for comparative analysis of the diversification and adaptation of fishes in Sillaginidae.
Project description:Silver sillago, Sillago sihama is a member of the family Sillaginidae and found in all Chinese inshore waters. It is an emerging commercial marine aquaculture species in China. In this study, high-quality chromosome-level reference genome of S. sihama was first constructed using PacBio Sequel sequencing and high-throughput chromosome conformation capture (Hi-C) technique. A total of 66.16 Gb clean reads were generated by PacBio sequencing platforms. The genome-scale was 521.63?Mb with 556 contigs, and 13.54?Mb of contig N50 length. Additionally, Hi-C scaffolding of the genome resulted in 24 chromosomes containing 96.93% of the total assembled sequences. A total of 23,959 protein-coding genes were predicted in the genome, and 96.51% of the genes were functionally annotated in public databases. A total of 71.86 Mb repetitive elements were detected, accounting for 13.78% of the genome. The phylogenetic relationships of silver sillago with other teleosts showed that silver sillago was separated from the common ancestor of Sillago sinica ?7.92?Ma. Comparative genomic analysis of silver sillago with other teleosts showed that 45 unique and 100 expansion gene families were identified in silver sillago. In this study, the genomic resources provide valuable reference genomes for functional genomics research of silver sillago.
Project description:Jia-Guang Xiao, Na Song, Zhi-Qiang Han, and Tian-Xiang Gao (2016) Reliance only on morphology to identify fishes to the species level is challenging when the diagnostic characters are similar among related taxa. Within the genus Sillago, differences among some nominal species are generally small and restricted to a few characters. In this study, a new species of Sillago (Sillago shaoi sp. nov.) was described using morphology and genetic analysis of DNA barcoding. The morphological results differentiated S. shaoi sp. nov. from eight other Sillago spp. Genetic analysis verified both the validity of the current taxonomy and the relationships between the new species and other Sillago species. S. shaoi sp. nov. formed a monophyletic group as a distinct phylogenetic species and showed strong genetic divergence from others. The present study also revealed that the COI gene was an effective molecular marker for identifying Sillago species.
Project description:Sillago species lives in the demersal environments and face multiple stressors, such as localized oxygen depletion, sulfide accumulation, and high turbidity. In this study, we performed transcriptome analyses of seven Sillago species to provide insights into the phylogeny and positively selected genes of this species. After de novo assembly, 82,024, 58,102, 63,807, 85,990, 102,185, 69,748, and 102,903 unigenes were generated from S. japonica, S. aeolus, S. sp.1, S. sihama, S. sp.2, S. parvisquamis, and S. sinica, respectively. Furthermore, 140 shared orthologous exon markers were identified and then applied to reconstruct the phylogenetic relationships of the seven Sillago species. The reconstructed phylogenetic structure was significantly congruent with the prevailing morphological and molecular biological view of Sillago species relationships. In addition, a total of 44 genes were identified to be positively selected, and these genes were potential participants in the stress response, material (carbohydrate, amino acid and lipid) and energy metabolism, growth and differentiation, embryogenesis, visual sense, and other biological processes. We suspected that these genes possibly allowed Sillago species to increase their ecological adaptation to multiple environmental stressors.
Project description:The genetic adaptations of various organisms to heterogeneous environments in the northwestern Pacific remain poorly understood. Heterogeneous genomic divergence among populations may reflect environmental selection. Advancing our understanding of the mechanisms by which organisms adapt to different temperatures in response to climate change and predicting the adaptive potential and ecological consequences of anthropogenic global warming are critical. We sequenced the whole genomes of Japanese whiting ( <i>Sillago japonica</i>) specimens collected from different latitudinal locations along the coastal waters of China and Japan to detect possible thermal adaptations. Using population genomics, a total of 5.48 million single nucleotide polymorphisms (SNPs) from five populations revealed a complete genetic break between the Chinese and Japanese groups, which was attributed to both geographic distance and local adaptation. The shared natural selection genes between two isolated populations (i.e., Zhoushan and Ise Bay/Tokyo Bay) indicated possible parallel evolution at the genetic level induced by temperature. These genes also indicated that the process of temperature selection on isolated populations is repeatable. Moreover, we observed natural candidate genes related to membrane fluidity, possibly underlying adaptation to cold environmental stress. These findings advance our understanding of the genetic mechanisms underlying the rapid adaptations of fish species. Species distribution projection models suggested that the Chinese and Japanese groups may have different responses to future climate change, with the former expanding and the latter contracting. The findings of this study enhance our understanding of genetic differentiation and adaptation to changing environments.
Project description:Sillago sihama has high economic value and is one of the most attractive aquaculture species in China. Despite its economic importance, studies of its genome have barely been performed. In this study, we conducted a first genomic survey of S. sihama using next-generation sequencing (NGS). In total, 45.063 Gb of high-quality sequence data were obtained. For the 17-mer frequency distribution, the genome size was estimated to be 508.50 Mb. The sequence repeat ratio was calculated to be 21.25%, and the heterozygosity ratio was 0.92%. Reads were assembled into 1,009,363 contigs, with a N50 length of 1362 bp, and then into 814,219 scaffolds, with a N50 length of 2173 bp. The average Guanine and Cytosine (GC) content was 45.04%. Dinucleotide repeats (56.55%) were the dominant form of simple sequence repeats (SSR).
Project description:Cobitoidea is one of the two superfamilies in Cypriniformes; however, few genomes have been sequenced for Cobitoidea fishes. Here, we obtained a total of 252.90 Gb of short Illumina reads and 31.60 Gb of long PacBio Sequel reads, representing approximate genome coverage of 256× and 50×, respectively. The final assembled genome is about 583.47 Mb with contig N50 sizes of 2.87 Mb, which accounts for 91.44% of the estimated genome size of 638.07 Mb. Using Hi-C-based chromatin contact maps, 99.31% of the genome assembly was placed into 25 chromosomes, and the N50 is 22.3 Mb. The gene annotation completeness was evaluated by BUSCO, and 2,470 of the 2,586 conserved genes (95.5%) could be found in our assembly. Repetitive elements were calculated to reach 33.08% of the whole genome. Moreover, we identified 25,406 protein-coding genes, of which 92.59% have been functionally annotated. This genome assembly will be a valuable genomic resource to understand the biology of the Tibetan loaches and will also set a stage for comparative analysis of the classification, diversification, and adaptation of fishes in Cobitoidea.
Project description:A new <i>Sillago</i> species, the black-banded sillago, <i>Sillago nigrofasciata</i> <b>sp. nov.</b>, is described based on 302 specimens sampled from the southern coast of China. Morphological comparisons have been conducted between the new species and ten other <i>Sillago</i> species. The results show that the new species is characterized by a black mid-lateral band below the lateral line when fresh; other characteristics are similar to those of <i>Sillago sihama</i> but subtle differences exist on the swim bladder between <i>Sillago nigrofasciata</i> sp. nov. and <i>S. sihama</i>. A detailed description and illustrations are provided for the new species. The validity of this new species is also supported by a genetic comparison using sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene.
Project description:Silver sillago (Sillago sihama) is a commercially important marine fish species in East Asia. In this study, we compared the transcriptome response to hypoxia stress in the gill tissue of S. sihama. The fish were divided into four groups, such as 1 h of hypoxia (hypoxia1h, DO = 1.5 ± 0.1 mg/L), 4 h of hypoxia (hypoxia4h, DO = 1.5 ± 0.1 mg/L), 4 h of reoxygen (reoxygen4h, DO = 8.0 ± 0.2 mg/L) after 4 h of hypoxia (DO = 1.5 mg/L), and normoxia or control (DO = 8.0 ± 0.2 mg/L) groups. Compared to the normoxia group, a total of 3550 genes were identified as differentially expressed genes (DEGs) (log2foldchange > 1 and padj < 0.05), including 1103, 1451 and 996 genes in hypoxia1h, hypoxia4h and reoxygen4h groups, respectively. Only 247 DEGs were differentially co-expressed in all treatment groups. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, DEGs were significantly enriched in steroid biosynthesis, biosynthesis of amino acids, glutathione metabolism and metabolism of xenobiotics by cytochrome P450, ferroptosis and drug metabolism-cytochrome P450 pathways. Of these, the cytochrome P450 (CYP) and glutathione S-transferase (GST) gene families were widely expressed. Our study represents the insights into the underlying molecular mechanisms of hypoxia stress.