Genome survey and development of polymorphic microsatellite loci for Sillago sihama based on Illumina sequencing technology

Genomic Characteristics of Okamejei kenojei and the Implications to Its Evolutionary Biology Study

Okamejei kenojei is an important economic species widely distributed in shallow coastal waters of the western North Pacific. In this study, the whole-genome survey analysis of O. kenojei was conducted to reveal its genomic characteristics. The genome size was estimated to be 2027.44 Mb, the repeat sequence content was 44.90%, and the heterozygous ratio was 1.04%. The mitochondrial genome excavated from the sequencing data was 16,974 bp, and it can form the closed circular molecule. The phylogenetic tree based on 13 protein-coding gene sequences supported the validity of Okamejei and assisted the conclusion that Raja porosa was the junior synonym of O. kenojei. Plenty of potential microsatellite loci were identified, and the distribution frequency was estimated to be approximately 236.3 SSRs per Mb. Among all motif types of microsatellites, the dinucleotide repeats were dominant (82.59%), followed by the trinucleotide repeats (8.05%), tetranucleotide repeats (5.80%), pentanucleotide repeats (2.83%), and hexanucleotide repeats (0.72%). The results of the present study could not only provide useful information for understanding the genome structure and functional characteristics of O. kenojei, but also lay the foundation for the subsequent mapping of the whole genome.

Microsatellites as Molecular Markers with Applications in Exploitation and Conservation of Aquatic Animal Populations

A large number of species and taxa has been studied for genetic polymorphism. Microsatellites have been known as hypervariable neutral molecular markers with the highest resolution power in comparison with any other markers. However, the discovery of a new type of molecular marker—single nucleotide polymorphism (SNP) has put the existing applications of microsatellites to the test. To ensure good resolution power in studies of populations and individuals, a number of microsatellite loci from 14 to 20 was often used, which corresponds to about 200 independent alleles. Recently, these numbers have tended to be increased by the application of genomic sequencing of expressed sequence tags (ESTs), and the choice of the most informative loci for genotyping depends on the aims of research. Examples of successful applications of microsatellite molecular markers in aquaculture, fisheries, and conservation genetics in comparison with SNPs have been summarized in this review. Microsatellites can be considered superior markers in such topics as kinship and parentage analysis in cultured and natural populations, the assessment of gynogenesis, androgenesis and ploidization. Microsatellites can be coupled with SNPs for mapping QTL. Microsatellites will continue to be used in research on genetic diversity in cultured stocks, and also in natural populations as an economically advantageous genotyping technique.

Genome Survey Sequencing and Genetic Background Characterization of Ilex chinensis Sims (Aquifoliaceae) Based on Next-Generation Sequencing

Ilex chinensis Sims. is an evergreen arbor species with high ornamental and medicinal value that is widely distributed in China. However, there is a lack of molecular and genomic data for this plant, which severely restricts the development of its relevant research. To obtain the whole reference genome, we first conducted a genome survey of I. chinensis by next-generation sequencing (NGS) to perform de novo whole-genome sequencing. As a result, our estimates using k-mer and flow cytometric analysis suggested the genome size of I. chinensis to be around 618-655 Mb, with the GC content, heterozygous rate, and repeat sequence rate of 37.52%, 1.1%, and 38%, respectively. A total of 334,649 microsatellite motifs were detected from the I. chinensis genome data, which will provide basic molecular markers for germplasm characterization, genetic diversity, and QTL mapping studies for I. chinensis. In summary, the I. chinensis genome is complex with high heterozygosity and few repeated sequences. Overall, this is the first report on the genome features of I. chinensis, and the information may lay a strong groundwork for future whole-genome sequencing and molecular breeding studies of this species.

Genome-wide survey reveals the phylogenomic relationships of Chirolophisjaponicus Herzenstein, 1890 (Stichaeidae, Perciformes)

Fish are the largest vertebrate group, consisting of more than 30 000 species with important ecological and economical value, while less than 3% of fish genomes have been published. Herein, a fish, Chirolophisjaponicus, was sequenced using the next-generation sequencing. Approximately 595.7 megabase pair of the C.japonicus genome was assembled (49 901 contigs with 42.61% GC contents), leading to a prediction of 46 729 protein-coding gene models. A total of 554 136 simple sequence repeats was identified in the whole genome of C.japonicus, and dinucleotide microsatellite motifs were the most abundant, accounting for 59.49%. Phylogenomic analysis of 16 genomes based on the 694 single-copy genes suggests that C.japonicus is closely related with Anarrhichthysocellatus, Cebidichthysviolaceus, and Pholisgunnellus. The results provide more thorough genetic information of C.japonicus and a theoretical basis and reference for further genome-wide analysis.

Genome-wide survey and genetic characteristics of Ophichthus evermanni based on Illumina sequencing platform

Ophichthidae fishes limit to continental shelf of all tropical and subtropical oceans and contain more than 350 species, representing the greatest specialization diversity in the order Anguiliformes. In the present study, we conducted a genome survey sequencing (GSS) analysis of Ophichthus evermanni by Illumina sequencing platform to briefly reveal its genomic characteristics and phylogenetic relationship. The first de novo assembled 1.97 Gb draft genome of O. evermanni was predicted based on K-mer analysis without obvious nucleotide bias. The heterozygosity ratio was 0.70%, and the sequence repeat ratio was calculated to be 43.30%. A total of 9016 putative coding genes were successfully predicted, in which 3587 unigenes were identified by gene ontology (GO) analysis and 4375 unigenes were classified into cluster of orthologous groups for enkaryotic complete genomes (KOG) functional categories. About 2,812,813 microsatellite motifs including mono-, di-, tri-, tetra-, penta- and hexanucleotide motifs were identified, with an occurrence frequency of 23.32%. The most abundant type was dinucleotide repeat motifs, accounting for 49.19% of the total repeat types. The mitochondrial genome, as a byproduct of GSS, was assembled to investigate the evolutionary relationships between O. evermanni and its relatives. Bayesian inference (BI) phylogenetic tree inferring from concatenated 12 protein-coding genes (PCGs) showed complicated relationships among Ophichthidae species, indicating a polyphyletic origin of the family. The results would achieve more thorough genetic information of snake eels and provide a theoretical basis and reference for further genome-wide analysis of O. evermanni.

Genome survey of Misgurnus anguillicaudatus to identify genomic information, simple sequence repeat (SSR) markers, and mitochondrial genome

BACKGROUND

The dojo loach Misgurnus anguillicaudatus is an important economic species in Asia because of its nutritional value and broad environmental adaptability. Despite its economic importance, genomic data for M. anguillicaudatus is currently unavailable.

METHODS AND RESULTS

In the present study, we conducted a genome survey of M. anguillicaudatus using next-generation sequencing technology. Its genome size was estimated to be 1105.97 Mb by using K-mer analysis, and its heterozygosity ratio, repeat sequence content, GC content were 1.45%, 58.98%, and 38.03%, respectively. A total of 376,357 microsatellite motifs were identified, and mononucleotides, with a frequency of 42.57%, were the most frequently repeated motifs, followed by 40.83% dinucleotide, 7.49% trinucleotide, 8.09% tetranucleotide, and 0.91% pentanucleotide motifs. The AC/GT, AAT/ATT, and ACAG/CTGT repeats were the most abundant motifs among dinucleotide, trinucleotide, and tetranucleotide motifs, respectively. Besides, the complete mitochondrial genome was sequenced. Based on the Maximum Likelihood and Bayesian inference analyses, M. anguillicaudatus yingde in this study was the "introgressed" mitochondrial type. Seventy microsatellite loci were randomly selected from detected SSR loci to test polymorphic, of which, 20 microsatellite loci were assessed in 30 individuals from a wild population. The number of alleles (Na), observed heterozygosity (Ho), and expected heterozygosity (He) per locus ranged from 7 to 19, 0.400 to 0.933, and 0.752 to 0.938, respectively. All 20 loci were highly informative (PIC > 0.700). Eight loci deviated from Hardy-Weinberg equilibrium after Bonferroni correction (P < 0.05).

CONCLUSIONS

This is the first report of genome survey sequencing in M. anguillicaudatus, genome information, mitochondrial genome, and microsatellite markers will be valuable for further studies on population genetic analysis, natural resource conservation, and molecular marker-assisted selective breeding.

Characterization of novel genotyping-by-sequencing (GBS)-based simple sequence repeats (SSRs) and their application for population genomics of Capoeta aculeata (Valenciennes, 1844)

BACKGROUND

The species Capoeta aculeata (Valenciennes, 1844) is one of the most important freshwater species endemic to Iran. However, the investigation of the population genetic structure of this species is limited by the low number of molecular markers currently described.

METHODS AND RESULTS

In this study, we implemented next generation sequencing technology to identify polymorphic microsatellite markers and investigate the population genetic structure of C. aculeata sampled from three geographical sites in Iran. We characterized and developed 36 novel polymorphic microsatellite markers and these loci were examined in 120 individuals from three populations occurring in the Zagros basin. The average number of alleles per locus varied from 1.7 to 16 (average = 7.89). The results showed that, the polymorphism information content (PIC) of these simple sequence repeat (SSR) loci varied from 0.254 to 0.888. The observed heterozygosity (H_O) per locus ranged from 0.170 to 0.881, while the expected heterozygosity (H_E) per locus was from 0.170 to 0.881. Among these SSR loci, 20 loci deviated significantly from the Hardy-Weinberg equilibrium after Bonferroni correction (p < 0.05).

CONCLUSIONS

These microsatellite markers could provide a valuable tool for future population and conservation genetics studies of C. aculeate and other closely related species.

Chromosomal-Level Genome Assembly of Silver Sillago (Sillago sihama)

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.