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bioRxiv2020

Utility of a high-resolution mouse single nucleotide polymorphism microarray assessed for rodent comparative genomics

In the study of genetic diversity in non-model species there is a notable lack of the low-cost, high resolution tools that are readily available for model organisms. Genotyping microarray technology for model organisms is well-developed, affordable, and potentially adaptable for cross-species hybridization. The Mouse Diversity Genotyping Array (MDGA), a single nucleotide polymorphism (SNP) genotyping tool designed for Mus musculus, was tested as a tool to survey genomic diversity of wild species for inter-order, inter-genus, and intra-genus comparisons. Application of the MDGA cross-species provides genetic distance information that reflects known taxonomic relationships reported previously between non-model species, but there is an underestimation of genetic diversity for non-Mus samples, indicated by a plateau in loci genotyped beginning 10-15 millions of years divergence from the house mouse. The number and types of samples included in datasets genotyped together must be considered in cross-species hybridization studies. The number of loci with heterozygous genotypes mapped to published genome sequences indicates potential for cross-species MDGA utility. A case study of seven deer mice yielded 159,797 loci (32% of loci queried by the MDGA) that were genotyped in these rodents. For one species, Peromyscus maniculatus, 6,075 potential polymorphic loci were identified. Cross-species utility of the MDGA provides needed genetic information for non-model species that are lacking genomic resources. Genotyping arrays are widely available, developed tools that are capable of capturing large amounts of genetic information in a single application, and represent a unique opportunity to identify genomic variation in closely related species that currently have a paucity of genomic information available. A candidate list of MDGA loci that can be utilized in cross-species hybridization studies was identified and may prove to be informative for rodent species that are known as environmental sentinels. Future studies may evaluate the utility of candidate SNP loci in populations of non-model rodents. Author SummaryThere is a need for a tool that can assay DNA sequence differences in species for which there is little or no DNA information available. One method of analyzing differences in DNA sequences in species with well-understood genomes is through a genotyping microarray, which has demonstrated utility cross-species. The Mouse Diversity Genotyping Array (MDGA) is a tool designed to examine known differences across the genome of the house mouse, Mus musculus. Given that related organisms share genetic similarity, the MDGA was tested for utility in identifying genome variation in other wild mice and rodents. Variation identified from distantly related species that were not of the same genus as the house mouse was an underestimate of the true amount of variation present in the genomes of wild species. Utility of the MDGA for wild species is best suited to mice from the same genus as the house mouse, and candidate variation identified can be tested in rodent populations in future studies. Identifying changes in genetic variation within populations of wild rodents can help researchers understand the links between specific genome changes and the ability to adapt to pressures in the environment, as well as better understand the evolution of rodents.

genomics↗

bioRxiv2021

Abundant secreted hydrolytic enzymes and secondary metabolite gene clusters in genomes of the Botryosphaeriaceae reflect their role as important plant pathogens

The Botryosphaeriaceae are important plant pathogens, but unique in their ability to establish asymptomatic infections that persist for extended periods in a latent state. In this study, we used comparative analyses to consider elements that might shed light on the genetic basis of the interactions of these fungi with their plant hosts. For this purpose, we characterised secreted hydrolytic enzymes, secondary metabolite biosynthetic gene clusters and considered general trends in genomic architecture using all available Botryosphaeriaceae genomes, and selected Dothideomycetes genomes. The Botryosphaeriaceae genomes were rich in carbohydrate-active enzymes (CAZymes), proteases, lipases and secondary metabolic biosynthetic gene clusters (BGCs) compared to other Dothideomycete genomes. The genomes of Botryosphaeria, Macrophomina, Lasiodiplodia and Neofusicoccum, in particular, had gene expansions of the major constituents of the secretome, notably CAZymes involved in plant cell wall degradation. The Botryosphaeriaceae genomes were shown to have moderate to high GC contents and most had low levels of repetitive DNA. The genomes were not compartmentalized based on gene and repeat densities, but genes of secreted enzymes were slightly more abundant in gene-sparse regions. The abundance of secreted hydrolytic enzymes and secondary metabolite BGCs in the genomes of Botryosphaeria, Macrophomina, Lasiodiplodia, and Neofusicoccum were similar to those in necrotrophic plant pathogens, but also endophytes of woody plants. The results provide a foundation for future comparative genomic analyses and hypothesis to explore the mechanisms underlying Botryosphaeriaceae host-plant interactions.

genomics↗

bioRxiv2021

Comparative genomics of Chinese and international isolates of Escherichia albertii: population structure and evolution of virulence and antimicrobial resistance

Escherichia albertii is a newly recognized species in the genus Escherichia that causes diarrhea. The population structure, genetic diversity and genomic features has not been fully examined. Here, 169 E. albertii isolates from different sources and regions in China were sequenced and combined with 312 publicly available genomes for phylogenetic and genomic analyses. The E. albertii population was divided into 2 clades and 8 lineages, with lineage 3 (L3), L5 and L8 more common in China. Clinical isolates were observed in all clades/lineages. Virulence genes were found to be distributed differently among lineages: subtypes of the intimin encoding gene eae and the cytolethal distending toxin (Cdt) gene cdtB were lineage associated, the second type three secretion system (ETT2) island was truncated in L3 and L6. Seven new eae subtypes and 1 new cdtB subtype (cdtB-VI) were found. Alarmingly, 85.9% of the Chinese E. albertii isolates were predicted to be multidrug resistant (MDR) with 35.9% harboured genes capable of conferring resistance to 10 to 14 different drug classes. By in silico multi-locus sequence typing, majority of the MDR isolates belonged to 4 STs (ST4638, ST4479, ST4633 and ST4488). Thirty-four intact plasmids carrying MDR and virulence genes, and 130 intact prophages were identified from 17 complete E. albertii genomes. Ten plasmid replicon types were found to be significantly associated with MDR. The 130 intact prophages were clustered into 5 groups, with group 5 prophages harbouring more virulence genes. Our findings provided fundamental insights into the population structure, virulence variation and MDR of E. albertii. Impact statementE. albertii is newly recognized foodborne pathogen causing diarrhea. Elucidation of its genomic features is important for surveillance and control of E. albertii infections. In this work, 169 E. albertii genomes from difference sources and regions in China were collected and sequenced, which contributed to the currently limited genomic data pool of E. albertii. In combination with 312 publicly available genomes from 14 additional countries, the population structure of E. albertii was defined. The presence and subtypes of virulence genes in different lineages were significantly different, indicating potential pathogenicity variation. Additionally, the presence of multidrug resistance (MDR) genes was alarmingly high in the Chinese dominated lineages. MDR associated STs and plasmid subtypes were identified, which could be used as sentinels for MDR surveillance. Moreover, the subtypes of plasmids and prophages were distributed differently across lineages, and were found to contribute to the acquisition of virulence and MDR genes of E. albertii. Altogether, this work reveals the diversity of E. albertii and characterized its genomic features in unprecedented detail. Data SummaryAll newly sequenced data in this work were deposited in National Center for Biotechnology Information (NCBI) under the BioProject of PRJNA693666, including 6 complete genomes and raw reads of 164 E. albertii isolates.

genomics↗

bioRxiv2021

Different evolutionary trends form the twilight zone of the bacterial pan-genome

The pan-genome is defined as the combined set of all genes in the gene pool of a species. Pan-genome analyses have been very useful in helping to understand different evolutionary dynamics of bacterial species: an open pan-genome often indicates a free-living lifestyle with metabolic versatility, while closed pan-genomes are linked to host-restricted, ecologically specialised bacteria. A detailed understanding of the species pan-genome has also been instrumental in tracking the phylodynamics of emerging drug resistance mechanisms and drug resistant pathogens. However, current approaches to analyse a species pan-genome do not take the species population structure into account, nor do they account for the uneven sampling of different lineages, as is commonplace due to over-sampling of clinically relevant representatives. Here we present the application of a population structure-aware approach for classifying genes in a pan-genome based on within-species distribution. We demonstrate our approach on a collection of 7,500 E. coli genomes, one of the most-studied bacterial species used as a model for an open pan-genome. We reveal clearly distinct groups of genes, clustered by different underlying evolutionary dynamics, and provide a more biologically informed and accurate description of the species pan-genome.

genomics↗

bioRxiv2021

The genome of the CTG(Ser1) yeast Scheffersomyces stipitis is plastic

Microorganisms need to adapt to environmental changes, and genome plasticity can lead to rapid adaptation to hostile environments by increasing genetic diversity. Here, we investigate genome plasticity in the CTG(Ser1) yeast Scheffersomyces stipitis, an organism with an enormous potential for second-generation biofuel production. We demonstrate that S. stipitis has an intrinsically plastic genome and that different S. stipitis isolates have genomes with distinct chromosome organisation. Real-time evolution experiments show that S. stipitis genome plasticity is common and rapid as extensive genomic changes with fitness benefits are detected following in vitro evolution experiments. Hybrid MinION Nanopore and Illumina genome sequencing identifies retrotransposons as major drivers of genome diversity. Indeed, the number and position of retrotransposons is different in different S. stipitis isolates, and retrotransposon-rich regions of the genome are sites of chromosome rearrangements. Our findings provide important insights into the adaptation strategies of the CTG (Ser1) yeast clade and have critical implications in the development of second-generation biofuels. These data highlight that genome plasticity is an essential factor to be considered for the development of sustainable S. stipitis platforms for second-generation biofuels production.

genomics↗

bioRxiv2021

Complex polyploid and hybrid species in an apomictic and sexual tropical forage grass group: genomic composition and evolution in Urochloa (Brachiaria) species

Background and AimsDiploid and polyploid Urochloa (including Brachiaria, Panicum and Megathyrsus species) C4 tropical forage grasses originating from Africa and now planted worldwide are important for food security and the environment, often being planted in marginal lands. We aimed to characterize the nature of their genomes, the repetitive DNA, and the genome composition of polyploids, leading to a model of the evolutionary pathways within the group including many apomictic species. MethodsSome 362 forage grass accessions from international germplasm collections were studied, and ploidy determined using an optimized flow cytometry method. Whole-genome survey sequencing and molecular cytogenetic analysis with in situ hybridization to chromosomes were used to identify chromosomes and genomes in Urochloa accessions belonging to the different agamic complexes. Key ResultsGenome structures are complex and variable, with multiple ploidies and genome compositions within the species, and no clear geographical patterns. Sequence analysis of nine diploid and polyploid accessions enabled identification of abundant genome-specific repetitive DNA motifs. In situ hybridization with a combination of repetitive DNA and genomic DNA probes, identified evolutionary divergence and allowed us to discriminate the different genomes present in polyploids. ConclusionsWe suggest a new coherent nomenclature for the genomes present. We develop a model of evolution at the whole-genome level in diploid and polyploid accessions showing processes of grass evolution. We support the retention of narrow species concepts for U. brizantha, U. decumbens, and U. ruziziensis. The results and model will be valuable in making rational choices of parents for new hybrids, assist in use of the germplasm for breeding and selection of Urochloa with improved sustainability and agronomic potential, and will assist in measuring and conserving biodiversity in grasslands.

genomics↗

bioRxiv2021

Refining the evolutionary time machine: an assessment of whole genome amplification using single historical Daphnia eggs

Whole genome sequencing is instrumental for the study of genome variation in natural populations, delivering important knowledge on genomic modifications and potential targets of natural selection at the population level. Large dormant eggbanks of aquatic invertebrates such as the keystone herbivore Daphnia, a microcrustacean widespread in freshwater ecosystems, provide detailed sedimentary archives to study genomic processes over centuries. To overcome the problem of limited DNA amounts in single Daphnia dormant eggs, we developed an optimised workflow for whole genome amplification (WGA), yielding sufficient amounts of DNA for downstream whole genome sequencing of individual historical eggs, including polyploid lineages. We compare two WGA kits, applied to recently produced Daphnia magna dormant eggs from laboratory cultures, and to historical dormant eggs of Daphnia pulicaria collected from Arctic lake sediment between 10y and 300y old. Resulting genome coverage breadth in most samples was ~70%, including those from >100y old isolates. Sequence read distribution was highly correlated among samples amplified with the same kit, but less correlated between kits. Despite this, a high percentage of genomic positions with SNPs in one or more samples (maximum of 74% between kits, and 97% within kits) were recovered at a depth required for genotyping. As a by-product of sequencing we obtained 100% coverage of the mitochondrial genomes even from the oldest isolates (~300y). The mtDNA provides an additional source for evolutionary studies of these populations. We provide an optimised workflow for WGA followed by whole genome sequencing including steps to minimise exogenous DNA.

genomics↗

bioRxiv2021

Comparative cytogenomics reveals genome reshuffling and centromere repositioning in the legume tribe Phaseoleae

The tribe Phaseoleae (Leguminosae; Papilionoideae) includes several legume crops with assembled genomes. Comparative genomic studies indicate the preservation of large genomic blocks among legumes, however, the chromosome dynamics during Phaseoleae evolution has not been investigated yet. We conducted a comparative genomic analysis to define an informative genomic block (GB) system and to reconstruct the ancestral Phaseoleae karyotype (APK). We defined the GBs based on the orthologous genes between Phaseolus vulgaris and Vigna unguiculata genomes. We searched for these GBs in different genome species belonging to the Phaseolinae (P. lunatus) and Glycininae subtribes (Amphicarpaea edgeworthii and Spatholobus suberectus), and in the Medicago truncaluta outgroup. To support our in silico analysis, we used oligo-FISH probes of P. vulgaris chromosomes 2 and 3 to paint the orthologous chromosomes of two non-sequenced Phaseolinae species (Macroptilium atropurpureum and Lablab purpureus). We inferred the APK with n = 11 and 19 GBs (A to S). We hypothesized five chromosome fusions that reduced the ancestral legume karyotype with n = 16 to n = 11 in APK. Furthermore, we identified the main rearrangements within Phaseolinae and observed an extensive centromere repositioning resulting from evolutionary new centromeres (ENC) in the Phaseolus lineage. Additionally, we demonstrated that the A. edgeworthii genome is more reshuffled than the dysploid S. suberectus genome, in which we could reconstruct the main events that lead the chromosome number reduction. The development of the GB system and the proposed APK provide useful approaches for future comparative genomic analyses of legume species.

genomics↗

bioRxiv2021

Comparative genomics of Xylella fastidiosa suggests determinants of host-specificity and expands its mobile genetic elements repertoire

The Gram-negative bacterium Xylella fastidiosa colonizes plant xylem vessels and is obligately vectored by xylem sap-feeding hemipteran insects. X. fastidiosa causes diseases in many plant species but in a variety of its plant hosts this bacterium behaves as a commensal endophyte. Originally confined to the Americas, infecting mainly grapevine, citrus and coffee plants, X. fastidiosa has spread to several plant species in Europe, causing devastating crop diseases. Although many pathogenicity and virulence factors have been identified in X. fastidiosa which enable the bacterium to successfully establish in the xylem tissue, the mechanisms by which distinct X. fastidiosa strains colonize and cause disease in specific plant hosts have not been fully elucidated. Here we present comparative analyses of 94 publicly available whole-genome sequences of X. fastidiosa strains with the goal of providing insights into plant host specificity determinants for this phytopathogen as well as of expanding the knowledge of its mobile genetic elements (MGE) content, mainly prophages. Our results revealed a pangenome of 4,549 protein coding sequences (CDSs) which is still open. The core- and accessory genomes comprise 954 and 2,219 CDSs, respectively. Phylogenetic tree construction using all core genome CDSs grouped the strains in three major clades of subspecies fastidiosa, multiplex and pauca, with subclades related to the strains sequence type (ST) obtained from multi-locus sequence typing (MLST). The geographic region where the strains were collected showed stronger association with the clades of X. fastidiosa strains rather than the plant species from which they were isolated. Among the CDS related to virulence and pathogenicity found in the core genome, those related to lipopolysaccharide (LPS) synthesis and trimeric autotransporter adhesins (TAA) are somewhat related with the plant host of a given strain according to phylogenetic inference. The X. fastidiosa accessory genome is represented by an abundant and heterogeneous mobilome, which includes a diversity of prophage regions. In summary, the genome comparisons reported here will enable a better understanding of the diversity of phylogenetically close genomes and warrant further investigation of LPS and TAAs as potential X. fastidiosa host-specificity determinants. Impact statementThe bacterium Xylella fastidiosa is a pathogen that infects many plant species and has caused devastating diseases in grapevine, citrus, coffee, and olive plants. This phytopathogen X. fastidiosa is original from the Americas and has emerged in Europe where it is causing severe economic losses for olive producers, mainly in Italy. Although many pathogenicity and virulence factors have been identified in X. fastidiosa, which enable this bacterium to successfully establish in the xylem vessels network, the mechanisms by which distinct X. fastidiosa strains colonize and cause disease in the different plant host species have not been fully elucidated. The comparative analyses of 94 whole-genome sequences from X. fastidiosa strains from diverse hosts and geographic regions provide insights into host specificity determinants for this phytopathogen as well as expand the knowledge of its mobile genetic elements (MGE) content, mainly prophages. Our results contribute for a better understanding of the diversity of phylogenetically close genomes and warrant further experimental investigation of lipopolysaccharide and trimeric autotransporter adhesins as potential host-specificity determinants for X. fastidiosa. Data summaryAll genomic sequences were accessed from publicly available GenBank RefSeq database at NCBI (National Center for Biotechnology Information). A full listing of NCBI accession numbers for X. fastidiosa strains described in this paper is available in Table S1 (available in the online version of this article).

genomics↗

bioRxiv2021

Shotgun metagenomics of soil invertebrate communities reflects taxonomy, biomass and reference genome properties

O_LIMetagenomics - shotgun sequencing of all DNA fragments from a community DNA extract - is routinely used to describe the composition, structure and function of microorganism communities. Advances in DNA sequencing and the availability of genome databases increasingly allow the use of shotgun metagenomics on eukaryotic communities. Metagenomics offers major advances in the recovery of biomass relationships in a sample, in comparison to taxonomic marker gene based approaches (metabarcoding). However, little is known about the factors which influence metagenomics data from eukaryotic communities, such as differences among organism groups, the properties of reference genomes and genome assemblies. C_LIO_LIWe evaluated how shotgun metagenomics records composition and biomass in artificial soil invertebrate communities. We generated mock communities of controlled biomass ratios from 28 species from all major soil mesofauna groups: mites, springtails, nematodes, tardigrades and potworms. We shotgun-sequenced these communities and taxonomically assigned them with a database of over 270 soil invertebrate genomes. C_LIO_LIWe recovered 90% of the species, and observed relatively high false positive detection rates. We found strong differences in reads assigned to different taxa, with some groups (e.g. springtails) consistently attracting more hits than others (e.g. enchytraeids). Original biomass could be predicted from read counts after considering these taxon-specific differences. Species with larger genomes, and with more complete assemblies consistently attracted more reads than species with smaller genomes. The GC content of the genome assemblies had no effect on the biomass-read relationships. C_LIO_LIThe results show considerable differences in taxon recovery and taxon specificity of biomass recovery from metagenomic sequence data. The properties of reference genomes and genome assemblies also influence biomass recovery, and they should be considered in metagenomic studies of eukaryotes. We provide a roadmap for investigating factors which influence metagenomics-based eukaryotic community reconstructions. Understanding these factors is timely as accessibility of DNA sequencing, and momentum for reference genomes projects show a future where the taxonomic assignment of DNA from any community sample becomes a reality. C_LI

genomics↗

bioRxiv2022

Genomics epidemiology analysis reveals hidden signatures of drug resistance in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) causes the majority of reported cases of human tuberculosis (TB), one of the deadliest infectious diseases worldwide. New diagnostic tools and approaches to detect drug-resistance must be introduced by 2025 to achieve the End-TB Strategy goals set for 2030 by the WHO. Genomic epidemiology of TB has allowed the expansion of catalogs listing genetic signatures of Mtb drug-resistance. However, very few Mtb strains from Latin America have participate in previous genomic epidemiologic efforts. Here we present the first functional genomic epidemiology study of drug-resistant Mtb strains in Mexico, incorporating the genomic characterization of 133 genomes, including 53 newly sequenced isolates, to provide a comprehensive phylogeographic analysis of drug resistant Mtb in Mexico. The study evidences the prevalence of Euro-American Lineage L4 (96.2%), featuring a uniform distribution of the sublineages X-type (33.08%), LAM (22.56%), and Haarlem (21.05%). Our results demonstrate low levels of agreement with traditional drug sensitivity tests (DST), raising concerns for drug-resistant isolates lacking any previously reported genetic signatures of resistance. Finally, we propose a novel functional networking tool (FuN-TB) to explore metabolic and cellular signatures of drug resistance. Applying functional genomics approaches to Latin American Mtb genomes will provide new drug-resistance screening targets that can contribute to bed side decision-making and advise local public policy. Abstract importanceWe presented the first phylogeographic analysis of Mycobacterium tuberculosis (Mtb) of Mexico. Our analysis integrates 133 genome sequences and is focused on the identification of genetic signatures associated to drug-resistance. The results show the geographic distribution of sublineages and drug-resistance phenotypic classes. Additionally, we propose a novel functional networking tool (FuN-TB) to explore metabolic and cellular signatures of drug resistance associated. We show for the first time that Mtb isolates from Mexico encode for region-specific genetic signarures of antimicrobial resistance. Applying functional genomics approaches to Latin American Mtb genomes will provide new drug-resistance screening targets that can contribute to bed side decision-making and advise local public policy.

genomics↗

bioRxiv2022

Genomic characteristics, virulence and antimicrobial resistance in avian pathogenic Escherichia coli MTR_BAU02 strain isolated from layer farms in Bangladesh

BackgroundColibacillosis, caused by avian pathogenic Escherichia coli (APEC), is one of the most significant infectious diseases affecting poultry worldwide. APEC is one of the leading causes of mortality and morbidity associated with significant economic losses in the poultry industry. ObjectiveThis study was aimed to determine the genomic diversity, virulence factor genes (VFGs) and antimicrobial resistance (AMR) genes in the APEC isolated from layer chickens using whole-genome sequencing (WGS). MethodAPEC MTR_BAU02 strain was isolated from the sick and dead birds. Genomic DNA from APEC MTR_BAU02 strain was extracted using commercial DNA extraction kit, WGS libraries were prepared using the Nextera DNA Flex Library Prep Kit, and finally, paired-end (2 x 250) WGS performed using Illumina MiSeq sequencer. ResultsThe genome size of strain APEC MTR_BAU02 is 4,924,680 bp with a GC content of 51.1% and 4,681 protein-coding sequences. Among the annotated WGS reads, 99.71% reads mapped to Enterobacteriaceae genomes. Based on the phylogenetic analysis of the APEC MTR_BAU02 genome and 99 reference genomes of E. coli, the APEC MTR_BAU02 genome showed sequence similarities with enterotoxigenic E. coli strains isolated from infections of different clinical severity. Metabolic functional annotations detected 380 SEED subsystems including genes coding for carbohydrate metabolism (17.34%), amino acid and derivatives (14.20%), protein metabolism (10.64%), cofactors, vitamins, prosthetic groups and pigments (7.49%), respiration (4.72%), membrane transport (4.49%), stress response (4.47%), motility and chemotaxis (4.46%), and virulence, disease and defense (2.22%). We also detected 92 VFGs and 122 AMR genes in the APEC MTR_BAU02 strain. ConclusionAssessment of these genomic features with functional genomic validation in commonly occurring serogroups of APEC will increase our understanding of the molecular pathogenesis, pave the way to early diagnosis and more effective control of colibacillosis, and improved animal welfare.

genomics↗

bioRxiv2022

Tracking the circulating SARS-CoV-2 variants in Turkey: Complete genome sequencing and molecular characterization of 1000 SARS-CoV-2 samples

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible coronavirus and has caused a pandemic of acute respiratory disease, named coronavirus disease 2019 (COVID-19). COVID-19 has a deep impact on public health as one of the most serious pandemics in the last century. Tracking SARS-CoV-2 is important for monitoring and assessing its evolution. This is only possible by detecting all mutations in the viral genome through genomic sequencing. Moreover, accurate detection of SARS-CoV-2 and tracking its mutations is also required for its correct diagnosis. Potential effects of mutations on the prognosis of the disease can be observed. Assignment of epidemiological lineages in an emerging pandemic requires efforts. To address this, we collected 1000 SARS-CoV-2 samples from different geographical regions in Turkey and analyze their genome comprehensively. To track the virus across Turkey we focus on 10 distinct cities in different geographic regions. Each SARS-CoV-2 genome was analyzed and named according to the nomenclature system of Nextclade and Pangolin Lineage. Furthermore, the frequency of the variations observed in 10 months was also determined by region. In this way, we have observed how the virus mutations and what kind of transmission mechanism it has. The effects of age and disease severity on lineage distribution were other considered parameters. The temporal rates of SARS-CoV-2 variants by time in Turkey were close to the global trend. This study is one of the most comprehensive whole genome analyses of SARS-CoV-2 that represents a general picture of the distribution of SARS-CoV-2 variations in Turkey in 2021. Author SummarySince the outbreak of the COVID-19 pandemic in 2019, the viral genome of SARS-CoV-2 was analysed intensively all over the world both to detect its zoonotic origin and the emerging variants worldwide together with the variants effect on the prognosis and treatment, respectively, of the infection. Remarkable COVID-19 studies were also made in Turkey as it was in the rest of the world. To date, indeed, almost all studies on COVID-19 in Turkey either sequenced only a small number of the viral genome or analysed the viral genome which was obtained from online databases. In respect thereof, our study constitutes a milestone regarding both the huge sample size consisting of 1000 viral genomes and the widespread geographic origin of the viral genome samples. Our study provides new insights both into the SARS-CoV-2 landscape of Turkey and the transmission of the emerging viral pathogen and its interaction with its vertebrate host.

genomics↗

bioRxiv2022

A map of cis-regulatory modules and constituent transcription factor binding sites in 80% of the mouse genome

Mouse is probably the most important model organism to study mammal biology and human diseases. A better understanding of the mouse genome will help understand the human genome, biology and diseases. However, despite the recent progress, characterization of the regulatory sequences in the mouse genome is still far from complete, limiting its use to understand the regulatory sequences in the human genome. Here, by integrating binding peaks in 9,060 transcription factor (TF) ChIP-seq datasets that cover 79.9% of the mouse mappable genome using an efficient pipeline, we were able to partition these binding peak-covered genome regions into a cis-regulatory module (CRM) candidate (CRMC) set and a non-CRMC sets. The CRMCs contain 912,197 putative CRMs and 38,554,729 TF binding sites (TFBSs) islands, covering 55.5% and 24.4% of the mappable genome, respectively. The CRMCs tend to be under strongly evolutionary constraints, indicating that they are likely cis-regulatory; while the non-CRMCs are largely selectively neutral, indicating that they are unlikely cis-regulatory. Based on evolutionary profiles of the genome positions, we further estimated that 63.8% and 27.4% of the mouse genome might code for CRMs and TFBSs, respectively. Validation using experimental data suggests that at least most of the CRMCs are authentic. Thus, this unprecedentedly comprehensive map of CRMs and TFBSs can be a good resource to guide experimental studies of regulatory genomes in mice and humans.

genomics↗

bioRxiv2022

The Gossypium herbaceum L. Wagad genome as a resource for understanding cotton domestication

Gossypium herbaceum is a species of cotton native to Africa and Asia that is one of the two domesticated diploids. Together with its sister-species G. arboreum, these A-genome taxa represent models of the extinct A-genome donor of modern polyploid cotton, which provide about 95% of cotton grown worldwide. As part of a larger effort to characterize variation and improve resources among diverse diploid and polyploid cotton genomes, we sequenced and assembled the genome of G. herbaceum cultivar (cv) Wagad, representing the first domesticated accession for this species. This chromosome-level genome was generated using a combination of PacBio long-read technology, HiC, and Bionano optical mapping and compared to existing genome sequences in cotton. We compare the genome of this cultivar to the existing genome of wild G. herbaceum subspecies africanum to elucidate changes in the G. herbaceum genome concomitant with domestication, and extend these analyses to gene expression using available RNA-seq. Our results demonstrate the utility of the G. herbaceum cv Wagad genome in understanding domestication in the diploid species, which could inform modern breeding programs.

genomics↗

bioRxiv2022

Realizing the promise of biodiversity genomics with highly accurate long reads

BackgroundGenerating the most contiguous, accurate genome assemblies given available sequencing technologies is a long-standing challenge in genome science. With the rise of long-read sequencing, assembly challenges have shifted from merely increasing contiguity to correctly assembling complex, repetitive regions of interest, ideally in a phased manner. At present, researchers largely choose between two types of long read data: longer, but less accurate sequences, or highly accurate, but shorter reads (i.e., >Q20 or 99% accurate). To better understand how these types of long-read data as well as scale of data (i.e., mean length and sequencing depth) influence genome assembly outcomes, we compared genome assemblies for a caddisfly, Hesperophylax magnus, generated with longer, but less accurate, Oxford Nanopore (ONT) R9.4.1 and highly accurate PacBio HiFi (HiFi) data. Next, we expanded this comparison to consider the influence of highly accurate long-read sequence data on genome assemblies across 6,750 plant and animal genomes. For this broader comparison, we used HiFi data as a surrogate for highly accurate long-reads broadly as we could identify when they were used from GenBank metadata. ResultsHiFi reads outperformed ONT reads in all assembly metrics tested for the caddisfly data set and allowed for accurate assembly of the repetitive [~]20 Kb H-fibroin gene. Across plants and animals, genome assemblies that incorporated HiFi reads were also more contiguous. For plants, the average HiFi assembly was 501% more contiguous (mean contig N50 = 20.5 Mb) than those generated with any other long-read data (mean contig N50 = 4.1 Mb). For animals, HiFi assemblies were 226% more contiguous (mean contig N50 = 20.9 Mb) versus other long-read assemblies (mean contig N50 = 9.3 Mb). In plants, we also found limited evidence that HiFi may offer a unique solution for overcoming genomic complexity that scales with assembly size. ConclusionsHighly accurate long-reads generated with HiFi or analogous technologies represent a key tool for maximizing genome assembly quality for a wide swath of plants and animals. This finding is particularly important when resources only allow for one type of sequencing data to be generated. Ultimately, to realize the promise of biodiversity genomics, we call for greater uptake of highly accurate long-reads in future studies.

genomics↗

bioRxiv2022

Imputation of ancient genomes

Due to postmortem DNA degradation, most ancient genomes sequenced to date have low depth of coverage, preventing the true underlying genotypes from being recovered. Genotype imputation has been put forward to improve genotyping accuracy for low-coverage genomes. However, it is unknown to what extent imputation of ancient genomes produces accurate genotypes and whether imputation introduces bias to downstream analyses. To address these questions, we downsampled 43 ancient genomes, 42 of which are high-coverage (above 10x) and three constitute a trio (mother, father and son), from different times and continents to simulate data with coverage in the range of 0.1x-2.0x and imputed these using state-of-the-art methods and reference panels. We assessed imputation accuracy across ancestries and depths of coverage. We found that ancient and modern DNA imputation accuracies were comparable. We imputed most of the 42 high-coverage genomes downsampled to 1x with low error rates (below 5%) and estimated higher error rates for African genomes, which are underrepresented in the reference panel. We used the ancient trio data to validate imputation and phasing results using an orthogonal approach based on Mendels rules of inheritance. This resulted in imputation and switch error rates of 1.9% and 2.0%, respectively, for 1x genomes. We further compared the results of downstream analyses between imputed and high-coverage genomes, notably principal component analysis (PCA), genetic clustering, and runs of homozygosity (ROH). For these three approaches, we observed similar results between imputed and high-coverage genomes using depths of coverage of at least 0.5x, except for African genomes, for which the decreased imputation accuracy impacted ROH estimates. Altogether, these results suggest that, for most populations and depths of coverage as low as 0.5x, imputation is a reliable method with potential to expand and improve ancient DNA studies.

genomics↗

bioRxiv2022

The High-quality genome assembly of Lactarius hatsudake

Lactarius hatsudake is a species of Lactarius commonly found in pine forests, is edible with a delicious and nutritious fruiting body and exhibits medicinal properties. It is an ideal natural multi-functional food with bioactive components including fungal polysaccharides, crude fiber, unsaturated fatty acids, nucleic acid derivatives, various amino acids, and vitamins. However, biological and genomic analyses of this mycorrhizal mushroom are sparse, thereby hindering large-scale cultivation. Previously, we isolated and screened L. hatsudake JH5 strains and have applied our garnered knowledge to the large-scale cultivation of mycorrhizal seedlings. In this study, we produced a high-quality genome assembly of L. hatsudake JH5 by combining Illumina paired-end (PE) and PacBio single molecule real-time (SMRT) sequencing, resulting in PacBio SMRT reads of 7.67 Gb and Illumina Pair-End reads of 1560 Mb. Based on the distribution of k-mer frequencies, the genome size of this strain was estimated to be 63.84 Mb (1.14% heterozygosity). Based on de novo genome assembly, the final genome size was determined to be 76.7 Mb, with scaffold N50 of 223.2 kb and N90 of 54.5 kb, and a GC content of 54.38%. BUSCO assessment showed that genome completeness was 89.0%. The N50 length of the JH5 genome was 43.6% longer than that of the previously published L. hatsudake MG20 genome. This high-quality L. hatsudake genome assembly will facilitate research on the functional genome, molecular breeding, yield enhancement and sustainability of L. hatsudake cultivation.

genomics↗