High-confidence Single Nucleotide Polymorphisms Research Articles

Enhancement of Glen Moy x Latham raspberry linkage map using GbS to further understand control of developmental processes leading to fruit ripening

BackgroundThe changing climate is altering timing of key fruit ripening processes and increasing the occurrence of fruit defects. To improve our understanding of the genetic control of raspberry fruit development an enhanced genetic linkage map was developed and used to examine ripening phenotypic data.ResultsIn this study we developed an enhanced genetic linkage map for the raspberry cvs. Glen Moy x Latham reference mapping population using genotyping by sequencing (GbS). Alignment to a newly sequenced draft reference genome of red raspberry, cultivar (cv.) Glen Moy, identified 8019 single nucleotide polymorphisms (SNPs). After stringent filtering to take account of read coverage over all the progeny individuals, association with a single chromosome, heterozygosity and marker regression mapping, 2348 high confidence SNPs were retained and integrated with an existing raspberry genetic map. The linkage map contained many more SNPs segregating in Latham than in Glen Moy. This caused difficulties in quantitative trait loci (QTL) mapping with standard software and a novel analysis based on a hidden Markov model was used to improve the mapping. QTL mapping using the newly generated dense genetic map not only corroborated previously identified genetic locations but also provided additional genetic elements controlling fruit ripening in raspberry.ConclusionThe high-density GbS map located the QTL peaks more precisely than in earlier studies, aligned the QTLs with Glen Moy genome scaffolds, narrowed the range of potential candidate genes to these regions that can be utilised in other populations or in gene expression studies to confirm their role and increased the repertoire of markers available to understand the genetic control of fruit ripening traits.

Diversity and Genome Analysis of Australian and Global Oilseed Brassica napus L. Germplasm Using Transcriptomics and Whole Genome Re-sequencing.

Intensive breeding of Brassica napus has resulted in relatively low diversity, such that B. napus would benefit from germplasm improvement schemes that sustain diversity. As such, samples representative of global germplasm pools need to be assessed for existing population structure, diversity and linkage disequilibrium (LD). Complexity reduction genotyping-by-sequencing (GBS) methods, including GBS-transcriptomics (GBS-t), enable cost-effective screening of a large number of samples, while whole genome re-sequencing (WGR) delivers the ability to generate large numbers of unbiased genomic single nucleotide polymorphisms (SNPs), and identify structural variants (SVs). Furthermore, the development of genomic tools based on whole genomes representative of global oilseed diversity and orientated by the reference genome has substantial industry relevance and will be highly beneficial for canola breeding. As recent studies have focused on European and Chinese varieties, a global diversity panel as well as a substantial number of Australian spring types were included in this study. Focusing on industry relevance, 633 varieties were initially genotyped using GBS-t to examine population structure using 61,037 SNPs. Subsequently, 149 samples representative of global diversity were selected for WGR and both data sets used for a side-by-side evaluation of diversity and LD. The WGR data was further used to develop genomic resources consisting of a list of 4,029,750 high-confidence SNPs annotated using SnpEff, and SVs in the form of 10,976 deletions and 2,556 insertions. These resources form the basis of a reliable and repeatable system allowing greater integration between canola genomics studies, with a strong focus on breeding germplasm and industry applicability.

Extensive Genetic Diversity is Present within North American Switchgrass Germplasm.

Switchgrass ( is a perennial native North American grass present in two ecotypes: upland, found primarily in the northern range of switchgrass habitats, and lowland, found largely in the southern reaches of switchgrass habitats. Previous studies focused on a diversity panel of primarily northern switchgrass, so to expand our knowledge of genetic diversity in a broader set of North American switchgrass, exome capture sequence data were generated for 632 additional, primarily lowland individuals. In total, over 37 million single nucleotide polymorphisms (SNPs) were identified and a set of 1.9 million high-confidence SNPs were obtained from 1169 individuals from 140 populations (67 upland, 65 lowland, 8 admixed) were used in downstream analyses of genetic diversity and population structure. Seven separate population groups were identified with moderate genetic differentiation [mean fixation index (Fst) estimate of 0.06] between the lowland and the upland populations. Ecotype-specific and population-specific SNPs were identified for use in germplasm evaluations. Relative to rice ( L.), maize ( L.), soybean [ (L.) Merr.], and Gaertn., analyses of nucleotide diversity revealed a high degree of genetic diversity (0.0135) across all individuals, consistent with the outcrossing mode of reproduction and the polyploidy of switchgrass. This study supports the hypothesis that repeated glaciation events, ploidy barriers, and restricted gene flow caused by flowering time differences have resulted in distinct gene pools across ecotypes and geographic regions. These data provide a resource to associate alleles with traits of interest for forage, restoration, and biofuel feedstock efforts in switchgrass.

A SNP resource for studying North American moose

Background: Moose ( Alces alces) colonized the North American continent from Asia less than 15,000 years ago, and spread across the boreal forest regions of Canada and the northern United States (US). Contemporary populations have low genetic diversity, due either to low number of individuals in the original migration (founder effect), and/or subsequent population bottlenecks in North America. Genetic tests based on informative single nucleotide polymorphism (SNP) markers are helpful in forensic and wildlife conservation activities, but have been difficult to develop for moose, due to the lack of a reference genome assembly and whole genome sequence (WGS) data. Methods: WGS data were generated for four individual moose from the US states of Alaska, Idaho, Wyoming, and Vermont with minimum and average genome coverage depths of 14- and 19-fold, respectively. Cattle and sheep reference genomes were used for aligning sequence reads and identifying moose SNPs. Results: Approximately 11% and 9% of moose WGS reads aligned to cattle and sheep genomes, respectively. The reads clustered at genomic segments, where sequence identity between these species was greater than 95%. In these segments, average mapped read depth was approximately 19-fold. Sets of 46,005 and 36,934 high-confidence SNPs were identified from cattle and sheep comparisons, respectively, with 773 and 552 of those having minor allele frequency of 0.5 and conserved flanking sequences in all three species. Among the four moose, heterozygosity and allele sharing of SNP genotypes were consistent with decreasing levels of moose genetic diversity from west to east. A minimum set of 317 SNPs, informative across all four moose, was selected as a resource for future SNP assay design. Conclusions: All SNPs and associated information are available, without restriction, to support development of SNP-based tests for animal identification, parentage determination, and estimating relatedness in North American moose.

A SNP resource for studying North American moose.

Background: Moose ( Alces alces) colonized the North American continent from Asia less than 15,000 years ago, and spread across the boreal forest regions of Canada and the northern United States (US). Contemporary populations have low genetic diversity, due either to low number of individuals in the original migration (founder effect), and/or subsequent population bottlenecks in North America. Genetic tests based on informative single nucleotide polymorphism (SNP) markers are helpful in forensic and wildlife conservation activities, but have been difficult to develop for moose, due to the lack of a reference genome assembly and whole genome sequence (WGS) data. Methods: WGS data were generated for four individual moose from the US states of Alaska, Idaho, Wyoming, and Vermont with minimum and average genome coverage depths of 14- and 19-fold, respectively. Cattle and sheep reference genomes were used for aligning sequence reads and identifying moose SNPs. Results: Approximately 11% and 9% of moose WGS reads aligned to cattle and sheep genomes, respectively. The reads clustered at genomic segments, where sequence identity between these species was greater than 95%. In these segments, average mapped read depth was approximately 19-fold. Sets of 46,005 and 36,934 high-confidence SNPs were identified from cattle and sheep comparisons, respectively, with 773 and 552 of those having minor allele frequency of 0.5 and conserved flanking sequences in all three species. Among the four moose, heterozygosity and allele sharing of SNP genotypes were consistent with decreasing levels of moose genetic diversity from west to east. A minimum set of 317 SNPs, informative across all four moose, was selected as a resource for future SNP assay design. Conclusions: All SNPs and associated information are available, without restriction, to support development of SNP-based tests for animal identification, parentage determination, and estimating relatedness in North American moose.

Genetic Characterization of the Soybean Nested Association Mapping Population.

A set of nested association mapping (NAM) families was developed by crossing 40 diverse soybean [ (L.) Merr.] genotypes to the common cultivar. The 41 parents were deeply sequenced for SNP discovery. Based on the polymorphism of the single-nucleotide polymorphisms (SNPs) and other selection criteria, a set of SNPs was selected to be included in the SoyNAM6K BeadChip for genotyping the parents and 5600 RILs from the 40 families. Analysis of the SNP profiles of the RILs showed a low average recombination rate. We constructed genetic linkage maps for each family and a composite linkage map based on recombinant inbred lines (RILs) across the families and identified and annotated 525,772 high confidence SNPs that were used to impute the SNP alleles in the RILs. The segregation distortion in most families significantly favored the alleles from the female parent, and there was no significant difference of residual heterozygosity in the euchromatic vs. heterochromatic regions. The genotypic datasets for the RILs and parents are publicly available and are anticipated to be useful to map quantitative trait loci (QTL) controlling important traits in soybean.

Development of SNP markers based on transcriptome sequences and their application in germplasm identification in radish (Raphanus sativus L.)

Single nucleotide polymorphism (SNP) is the most frequent form of DNA variation in the genome. The cleaved amplified polymorphic sequence (CAPS) and derived CAPS (dCAPS) are co-dominant and cost-effective markers for SNP genotyping. Recently, the large-scale transcriptome sequencing has greatly facilitated SNP detection, and the applications of CAPS/dCAPS markers have been successfully carried out in various plant species. However, SNP detection via transcriptome sequencing and development of CAPS/dCAPS markers remain limited in radish. In this study, 56,089 SNPs were detected in the radish transcriptome, and 4941 high-confidence SNPs were further filtered out and analyzed, which could alter the recognition sites of 222 restriction enzymes. The available frequency of different enzymes varied a great deal, and ten enzymes were selected for marker development. A total of 262 pairs of CAPS and 15 pairs of dCAPS primers were synthesized, among which 148 and six could generate polymorphic bands after enzyme digestion, respectively. Furthermore, the polymorphism information content (PIC) values of 154 SNP markers ranged from 0.0739 to 0.3750. In addition, 24 radish genotypes were gradually distinguished by six CAPS markers with the manual cultivar identification diagram (MCID) approach, indicating the feasibility of CAPS/dCAPS markers in genetic diversity analysis and germplasm identification. These newly developed SNP markers could enrich the types and numbers of functional markers, and could be valuable in facilitating gene tagging, genetic mapping, comparative genomic studies and marker-assisted selection (MAS) of important horticultural traits in radish.

Transcriptome sequencing and marker development in winged bean (Psophocarpus tetragonolobus; Leguminosae).

Winged bean, Psophocarpus tetragonolobus (L.) DC., is similar to soybean in yield and nutritional value but more viable in tropical conditions. Here, we strengthen genetic resources for this orphan crop by producing a de novo transcriptome assembly and annotation of two Sri Lankan accessions (denoted herein as CPP34 [PI 491423] and CPP37 [PI 639033]), developing simple sequence repeat (SSR) markers, and identifying single nucleotide polymorphisms (SNPs) between geographically separated genotypes. A combined assembly based on 804,757 reads from two accessions produced 16,115 contigs with an N50 of 889 bp, over 90% of which has significant sequence similarity to other legumes. Combining contigs with singletons produced 97,241 transcripts. We identified 12,956 SSRs, including 2,594 repeats for which primers were designed and 5,190 high-confidence SNPs between Sri Lankan and Nigerian genotypes. The transcriptomic data sets generated here provide new resources for gene discovery and marker development in this orphan crop, and will be vital for future plant breeding efforts. We also analyzed the soybean trypsin inhibitor (STI) gene family, important plant defense genes, in the context of related legumes and found evidence for radiation of the Kunitz trypsin inhibitor (KTI) gene family within winged bean.

An ultra-high density genetic linkage map of perennial ryegrass (Lolium perenne) using genotyping by sequencing (GBS) based on a reference shotgun genome assembly.

High density genetic linkage maps that are extensively anchored to assembled genome sequences of the organism in question are extremely useful in gene discovery. To facilitate this process in perennial ryegrass (Lolium perenne L.), a high density single nucleotide polymorphism (SNP)- and presence/absence variant (PAV)-based genetic linkage map has been developed in an F2 mapping population that has been used as a reference population in numerous studies. To provide a reference sequence to which to align genotyping by sequencing (GBS) reads, a shotgun assembly of one of the grandparents of the population, a tenth-generation inbred line, was created using Illumina-based sequencing. The assembly was based on paired-end Illumina reads, scaffolded by mate pair and long jumping distance reads in the range of 3-40 kb, with >200-fold initial genome coverage. A total of 169 individuals from an F2 mapping population were used to construct PstI-based GBS libraries tagged with unique 4-9 nucleotide barcodes, resulting in 284 million reads, with approx. 1·6 million reads per individual. A bioinformatics pipeline was employed to identify both SNPs and PAVs. A core genetic map was generated using high confidence SNPs, to which lower confidence SNPs and PAVs were subsequently fitted in a straightforward binning approach. The assembly comprises 424 750 scaffolds, covering 1·11 Gbp of the 2·5 Gbp perennial ryegrass genome, with a scaffold N50 of 25 212 bp and a contig N50 of 3790 bp. It is available for download, and access to a genome browser has been provided. Comparison of the assembly with available transcript and gene model data sets for perennial ryegrass indicates that approx. 570 Mbp of the gene-rich portion of the genome has been captured. An ultra-high density genetic linkage map with 3092 SNPs and 7260 PAVs was developed, anchoring just over 200 Mb of the reference assembly. The combined genetic map and assembly, combined with another recently released genome assembly, represent a significant resource for the perennial ryegrass genetics community.

Genotyping-by-sequencing to remap QTL for type II Fusarium head blight and leaf rust resistance in a wheat–tall wheatgrass introgression recombinant inbred population

Fusarium graminearum Schwabe (Fusarium head blight, FHB) and Puccinia triticina Eriks (leaf rust) are two major fungal pathogens posing a continuous threat to the wheat crop; consequently, identifying resistance genes from various sources is always of importance to wheat breeders. We identified tightly linked single nucleotide polymorphism (SNP) markers for the FHB resistance quantitative trait locus (QTL) Qfhs.pur-7EL and the leaf rust resistance locus Lr19 using genotyping-by-sequencing (GBS) in a wheat–tall wheatgrass introgression-derived recombinant inbred line (RIL) population. One thousand and seven hundred high-confidence SNPs were used to conduct the linkage and QTL analysis. Qfhs.pur-7EL was mapped to a 2.9 cM region containing four markers within a 43.6 cM segment of wheatgrass chromosome 7el2 that was translocated onto wheat chromosome 7DL. Lr19 from 7el1 was mapped to a 1.21 cM region containing two markers in the same area, in repulsion. Five lines were identified with the resistance-associated SNP alleles for Qfhs.pur-7EL and Lr19 in coupling. Two SNP markers in the Qfhs.pur-7EL region were converted into PCR-based KASP markers. Investigation of the genetic characteristics of the parental lines of this RIL population indicated that they are translocation lines in two different wheat cultivar genetic backgrounds instead of 7E–7D substitution lines in Thatcher wheat background, as previously reported in the literature.

Analytical workflow of double-digest restriction site-associated DNA sequencing based on empirical and in silico optimization in tomato.

Double-digest restriction site-associated DNA sequencing (ddRAD-Seq) enables high-throughput genome-wide genotyping with next-generation sequencing technology. Consequently, this method has become popular in plant genetics and breeding. Although computational in silico prediction of restriction sites from the genome sequence is recognized as an effective approach for choosing the restriction enzymes to be used, few reports have evaluated the in silico predictions in actual experimental data. In this study, we designed and demonstrated a workflow for in silico and empirical ddRAD-Seq analysis in tomato, as follows: (i) in silico prediction of optimum restriction enzymes from the reference genome, (ii) verification of the prediction by actual ddRAD-Seq data of four restriction enzyme combinations, (iii) establishment of a computational data processing pipeline for high-confidence single nucleotide polymorphism (SNP) calling, and (iv) validation of SNP accuracy by construction of genetic linkage maps. The quality of SNPs based on de novo assembly reference of the ddRAD-Seq reads was comparable with that of SNPs obtained using the published reference genome of tomato. Comparisons of SNP calls in diverse tomato lines revealed that SNP density in the genome influenced the detectability of SNPs by ddRAD-Seq. In silico prediction prior to actual analysis contributed to optimization of the experimental conditions for ddRAD-Seq, e.g. choices of enzymes and plant materials. Following optimization, this ddRAD-Seq pipeline could help accelerate genetics, genomics, and molecular breeding in both model and non-model plants, including crops.

Identification of pleiotropic genes and gene sets underlying growth and immunity traits: a case study on Meishan pigs

Both growth and immune capacity are important traits in animal breeding. The animal quantitative trait loci (QTL) database is a valuable resource and can be used for interpreting the genetic mechanisms that underlie growth and immune traits. However, QTL intervals often involve too many candidate genes to find the true causal genes. Therefore, the aim of this study was to provide an effective annotation pipeline that can make full use of the information of Gene Ontology terms annotation, linkage gene blocks and pathways to further identify pleiotropic genes and gene sets in the overlapping intervals of growth-related and immunity-related QTLs. In total, 55 non-redundant QTL overlapping intervals were identified, 1893 growth-related genes and 713 immunity-related genes were further classified into overlapping intervals and 405 pleiotropic genes shared by the two gene sets were determined. In addition, 19 pleiotropic gene linkage blocks and 67 pathways related to immunity and growth traits were discovered. A total of 343 growth-related genes and 144 immunity-related genes involved in pleiotropic pathways were also identified, respectively. We also sequenced and genotyped 284 individuals from Chinese Meishan pigs and European pigs and mapped the single nucleotide polymorphisms (SNPs) to the pleiotropic genes and gene sets that we identified. A total of 971 high-confidence SNPs were mapped to the pleiotropic genes and gene sets that we identified, and among them 743 SNPs were statistically significant in allele frequency between Meishan and European pigs. This study explores the relationship between growth and immunity traits from the view of QTL overlapping intervals and can be generalized to explore the relationships between other traits.

Construction of the High-Density Genetic Linkage Map and Chromosome Map of Large Yellow Croaker (Larimichthys crocea).

High-density genetic maps are essential for genome assembly, comparative genomic analysis and fine mapping of complex traits. In this study, 31,191 single nucleotide polymorphisms (SNPs) evenly distributed across the large yellow croaker (Larimichthys crocea) genome were identified using restriction-site associated DNA sequencing (RAD-seq). Among them, 10,150 high-confidence SNPs were assigned to 24 consensus linkage groups (LGs). The total length of the genetic linkage map was 5451.3 cM with an average distance of 0.54 cM between loci. This represents the densest genetic map currently reported for large yellow croaker. Using 2889 SNPs to target specific scaffolds, we assigned 533 scaffolds, comprising 421.44 Mb (62.04%) of the large yellow croaker assembled sequence, to the 24 linkage groups. The mapped assembly scaffolds in large yellow croaker were used for genome synteny analyses against the stickleback (Gasterosteus aculeatus) and medaka (Oryzias latipes). Greater synteny was observed between large yellow croaker and stickleback. This supports the hypothesis that large yellow croaker is more closely related to stickleback than to medaka. Moreover, 1274 immunity-related genes and 195 hypoxia-related genes were mapped to the 24 chromosomes of large yellow croaker. The integration of the high-resolution genetic map and the assembled sequence provides a valuable resource for fine mapping and positional cloning of quantitative trait loci associated with economically important traits in large yellow croaker.

Diversity and population structure of northern switchgrass as revealed through exome capture sequencing.

Panicum virgatum L. (switchgrass) is a polyploid, perennial grass species that is native to North America, and is being developed as a future biofuel feedstock crop. Switchgrass is present primarily in two ecotypes: a northern upland ecotype, composed of tetraploid and octoploid accessions, and a southern lowland ecotype, composed of primarily tetraploid accessions. We employed high-coverage exome capture sequencing (~2.4Tb) to genotype 537 individuals from 45 upland and 21 lowland populations. From these data, we identified ~27million single-nucleotide polymorphisms (SNPs), of which 1590653 high-confidence SNPs were used in downstream analyses of diversity within and between the populations. From the 66 populations, we identified five primary population groups within the upland and lowland ecotypes, a result that was further supported through genetic distance analysis. We identified conserved, ecotype-restricted, non-synonymous SNPs that are predicted to affect the protein function of CONSTANS (CO) and EARLY HEADING DATE 1 (EHD1), key genes involved in flowering, which may contribute to the phenotypic differences between the two ecotypes. We also identified, relative to the near-reference Kanlow population, 17 228 genes present in more copies than in the reference genome (up-CNVs), 112 630 genes present in fewer copies than in the reference genome (down-CNVs) and 14430 presence/absence variants (PAVs), affecting a total of 9979 genes, including two upland-specific CNV clusters. In total, 45719 genes were affected by an SNP, CNV, or PAV across the panel, providing a firm foundation to identify functional variation associated with phenotypic traits of interest for biofuel feedstock production.

From promise to practice: pairing non-invasive sampling with genomics in conservation.

Conservation genomics has become an increasingly popular term, yet it remains unclear whether the non-invasive sampling that is essential for many conservation-related studies is compatible with the minimum requirements for harnessing next-generation sequencing technologies. Here, we evaluated the feasibility of using genotyping-by-sequencing of non-invasively collected hair samples to simultaneously identify and genotype single nucleotide polymorphisms (SNPs) in a climate-sensitive mammal, the American pika (Ochotona princeps). We identified and genotyped 3,803 high-confidence SNPs across eight sites distributed along two elevational transects using starting DNA amounts as low as 1 ng. Fifty-five outlier loci were detected as candidate gene regions under divergent selection, constituting potential targets for future validation. Genome-wide estimates of gene diversity significantly and positively correlated with elevation across both transects, with all low elevation sites exhibiting significant heterozygote deficit likely due to inbreeding. More broadly, our results highlight a range of issues that must be considered when pairing genomic data collection with non-invasive sampling, particularly related to field sampling protocols for minimizing exogenous DNA, data collection strategies and quality control steps for enhancing target organism yield, and analytical approaches for maximizing cost-effectiveness and information content of recovered genomic data.

Development of molecular resources for the Chinese horseshoe crab Tachypleus tridentatus

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 24:17-24 (2015) - DOI: https://doi.org/10.3354/ab00632 Development of molecular resources for the Chinese horseshoe crab Tachypleus tridentatus Hongjun Li1, Ying Xia2, Yiyong Rao4, Shuxi Liu1, Jingjing Zhang1,5, Lizhe Cai3,4,* 1Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China 2Dalian Environmental Monitoring Center, Dalian 116023, PR China 3Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, Xiamen University, Xiamen 361102, PR China 4College of the Environment and Ecology, Xiamen University, Xiamen 361002, PR China 5Dalian Ocean University, Dalian 116023, PR China *Corresponding author: cailizhe@xmu.edu.cn ABSTRACT: The Chinese horseshoe crab Tachypleus tridentatus is an endangered marine benthic species of great biomedical value and scientific significance. In this study, T. tridentatus hemocyte transcriptome was sequenced to rapidly develop molecular resources using the Illumina paired-end sequencing platform. Deep sequencing generated a total of 38402764 reads that consisted of 7.7 Gbp raw data, which were assembled into 38759 unigenes with an average length of 668.6 bp. A total of 608 microsatellite loci and 71959 high-confidence single nucleotide polymorphisms were discovered. All the assembled unigenes were annotated by running BLASTx similarity searches on Nr, Swiss-Prot, COG, and KEGG databases; of which 17446 (45.0%) unigenes showed significant matches (E-value <1e-5) to known sequences in public databases. As determined through gene ontology annotation and KEGG pathway mapping, the functional annotation of the unigenes signified diverse biological functions and processes. Transcripts potentially involved in immune defense were identified among these genes. These transcripts included pattern recognition receptors, stress response genes, complement components, and immune effectors. This study provides important insights into the transcript sequences of T. tridentatus, which may facilitate studies on the conservation genetics and development of biomedical applications for T. tridentatus. KEY WORDS: Chinese horseshoe crab · Tachypleus tridentatus · Endangered species · Transcriptome · RNA-seq · Microsatellite · SNP · Conservation genomics · Biomedicine Full text in pdf format Supplementary material 1 Supplementary material 2 PreviousNextCite this article as: Li H, Xia Y, Rao Y, Liu S, Zhang J, Cai L (2015) Development of molecular resources for the Chinese horseshoe crab Tachypleus tridentatus. Aquat Biol 24:17-24. https://doi.org/10.3354/ab00632 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 24, No. 1. Online publication date: May 20, 2015 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2015 Inter-Research.

Genome-wide SNP identification for the construction of a high-resolution genetic map of Japanese flounder (Paralichthys olivaceus): applications to QTL mapping of Vibrio anguillarum disease resistance and comparative genomic analysis.

High-resolution genetic maps are essential for fine mapping of complex traits, genome assembly, and comparative genomic analysis. Single-nucleotide polymorphisms (SNPs) are the primary molecular markers used for genetic map construction. In this study, we identified 13,362 SNPs evenly distributed across the Japanese flounder (Paralichthys olivaceus) genome. Of these SNPs, 12,712 high-confidence SNPs were subjected to high-throughput genotyping and assigned to 24 consensus linkage groups (LGs). The total length of the genetic linkage map was 3,497.29 cM with an average distance of 0.47 cM between loci, thereby representing the densest genetic map currently reported for Japanese flounder. Nine positive quantitative trait loci (QTLs) forming two main clusters for Vibrio anguillarum disease resistance were detected. All QTLs could explain 5.1–8.38% of the total phenotypic variation. Synteny analysis of the QTL regions on the genome assembly revealed 12 immune-related genes, among them 4 genes strongly associated with V. anguillarum disease resistance. In addition, 246 genome assembly scaffolds with an average size of 21.79 Mb were anchored onto the LGs; these scaffolds, comprising 522.99 Mb, represented 95.78% of assembled genomic sequences. The mapped assembly scaffolds in Japanese flounder were used for genome synteny analyses against zebrafish (Danio rerio) and medaka (Oryzias latipes). Flounder and medaka were found to possess almost one-to-one synteny, whereas flounder and zebrafish exhibited a multi-syntenic correspondence. The newly developed high-resolution genetic map, which will facilitate QTL mapping, scaffold assembly, and genome synteny analysis of Japanese flounder, marks a milestone in the ongoing genome project for this species.

The Y-chromosome tree bursts into leaf: 13,000 high-confidence SNPs covering the majority of known clades.

Many studies of human populations have used the male-specific region of the Y chromosome (MSY) as a marker, but MSY sequence variants have traditionally been subject to ascertainment bias. Also, dating of haplogroups has relied on Y-specific short tandem repeats (STRs), involving problems of mutation rate choice, and possible long-term mutation saturation. Next-generation sequencing can ascertain single nucleotide polymorphisms (SNPs) in an unbiased way, leading to phylogenies in which branch-lengths are proportional to time, and allowing the times-to-most-recent-common-ancestor (TMRCAs) of nodes to be estimated directly. Here we describe the sequencing of 3.7 Mb of MSY in each of 448 human males at a mean coverage of 51×, yielding 13,261 high-confidence SNPs, 65.9% of which are previously unreported. The resulting phylogeny covers the majority of the known clades, provides date estimates of nodes, and constitutes a robust evolutionary framework for analyzing the history of other classes of mutation. Different clades within the tree show subtle but significant differences in branch lengths to the root. We also apply a set of 23 Y-STRs to the same samples, allowing SNP- and STR-based diversity and TMRCA estimates to be systematically compared. Ongoing purifying selection is suggested by our analysis of the phylogenetic distribution of nonsynonymous variants in 15 MSY single-copy genes.

Genotyping by sequencing transcriptomes in an evolutionary pre-breeding durum wheat population

The genetic diversity in durum wheat, Triticum turgidum durum, has been strongly reduced since the domestication of the wild Triticum turgidum dicoccoides. Monitoring durum wheat composite crosses incorporating related tetraploid taxa, such as wild and domesticated emmer wheat, is a suitable evolutionary pre-breeding method. Transcriptome sequencing paves the way for a genomic survey of single nucleotide polymorphisms (SNPs) segregating in such populations, offering the possibility of genotyping by sequencing to use these resources in genome-wide association studies (GWAS) and genomic selection (GS) programs. Evolutionary Pre-breeding pOpulation (EPO) is an evolutionary durum wheat pre-breeding population. Sequencing the transcriptome of 179 durum wheat lines (175 from EPO) led to the detection of 103,262 SNPs on two reference transcriptomes: one from the International Wheat Genome Sequencing Consortium and one assembled de novo on durum wheat. Using strict filtering to remove dubious heterozygous SNPs, EPO genetic diversity was eventually described with 76,188 high-confidence SNPs. The percentage of missing genotyping data depended on the expression level, and 88 individuals out of 175 were genotyped per SNP on average. Using the 3B pseudo-molecule of bread wheat, the transcription and diversity levels were shown to be higher in distal regions than in proximal regions, but SNPs were available throughout the chromosomes. Assuming good synteny with Hordeum, the trend was similar on the 14 chromosomes of the durum wheat genome. EPO hosts a high level of diversity, has a number of SNPs in low linkage disequilibrium (<40 Mb) and would be well suited for GWAS and GS programs.

Underlying genetic variation in the response of cultivated and wild soybean to enhanced ultraviolet-B radiation

Reductions in stratospheric ozone have resulted in increased levels of ultraviolet-B (UV-B, 280–315 nm) radiation reaching the earth’s surface. UV-B radiation can damage plant DNA and photosynthetic machinery. Therefore, enhanced UV-B levels would seriously affect crop production in several regions of the world. Here, we provide a comprehensive report of intraspecific variability in the response of soybean to UV-B radiation and the genetic variation underlying UV-B resistance. We evaluated 140 genotypes, including 94 Glycine max and 46 G. soja accessions, for their sensitivity to supplemental UV-B radiation. Differences in responses to elevated UV-B levels, such as changes in leaf area and aerial biomass, were observed among soybean genotypes, supporting the notion that there is intraspecific variability in this response in G. soja as well as G. max. To explore how genetic variation contributes to differences in UV-B resistance, we sequenced the most UV-B resistant (IT162669) and sensitive (Cheongjakong 3) genotypes at the whole-genome level. Based on their homology and functional annotation, 137 genes were determined to be “UV-B-related genes” in soybean, harboring almost 100 high-confidence single nucleotide polymorphisms between the two genotypes. Interestingly, we identified four genes with non-synonymous mutations that are related to plant protection mechanisms, such as the UV-protection, DNA damage repair and DNA damage tolerance pathways. Our results provide valuable information about UV-B-resistant soybean genotypes, UV-B-related soybean genes, and sequence variations between resistant and sensitive genotypes.