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Auto Tag: Genetic markers

April 21, 2020  |  

A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci.

Cannabis sativa is widely cultivated for medicinal, food, industrial, and recreational use, but much remains unknown regarding its genetics, including the molecular determinants of cannabinoid content. Here, we describe a combined physical and genetic map derived from a cross between the drug-type strain Purple Kush and the hemp variety “Finola.” The map reveals that cannabinoid biosynthesis genes are generally unlinked but that aromatic prenyltransferase (AP), which produces the substrate for THCA and CBDA synthases (THCAS and CBDAS), is tightly linked to a known marker for total cannabinoid content. We further identify the gene encoding CBCA synthase (CBCAS) and characterize its catalytic activity, providing insight into how cannabinoid diversity arises in cannabis. THCAS and CBDAS (which determine the drug vs. hemp chemotype) are contained within large (>250 kb) retrotransposon-rich regions that are highly nonhomologous between drug- and hemp-type alleles and are furthermore embedded within ~40 Mb of minimally recombining repetitive DNA. The chromosome structures are similar to those in grains such as wheat, with recombination focused in gene-rich, repeat-depleted regions near chromosome ends. The physical and genetic map should facilitate further dissection of genetic and molecular mechanisms in this commercially and medically important plant. © 2019 Laverty et al.; Published by Cold Spring Harbor Laboratory Press.

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April 21, 2020  |  

Genome analyses for the Tohoku Medical Megabank Project towards establishment of personalized healthcare.

Personalized healthcare (PHC) based on an individual’s genetic make-up is one of the most advanced, yet feasible, forms of medical care. The Tohoku Medical Megabank (TMM) Project aims to combine population genomics, medical genetics and prospective cohort studies to develop a critical infrastructure for the establishment of PHC. To date, a TMM CommCohort (adult general population) and a TMM BirThree Cohort (birth+three-generation families) have conducted recruitments and baseline surveys. Genome analyses as part of the TMM Project will aid in the development of a high-fidelity whole-genome Japanese reference panel, in designing custom single-nucleotide polymorphism (SNP) arrays specific to Japanese, and in estimation of the biological significance of genetic variations through linked investigations of the cohorts. Whole-genome sequencing from >3,500 unrelated Japanese and establishment of a Japanese reference genome sequence from long-read data have been done. We next aim to obtain genotype data for all TMM cohort participants (>150,000) using our custom SNP arrays. These data will help identify disease-associated genomic signatures in the Japanese population, while genomic data from TMM BirThree Cohort participants will be used to improve the reference genome panel. Follow-up of the cohort participants will allow us to test the genetic markers and, consequently, contribute to the realization of PHC.

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April 21, 2020  |  

Whole-genome sequencing reveals recent and frequent genetic recombination between clonal lineages of Cryphonectria parasitica in western Europe.

Changes in the mode of reproduction are frequently observed in invasive fungal populations. The ascomycete Cryphonectria parasitica, which causes Chestnut Blight, was introduced to Europe from North America and Asia in the 20th century. Previous genotyping studies based on ten microsatellite markers have identified several clonal lineages which have spread throughout western Europe, suggesting that asexuality was the main reproductive mode of this species during colonization, although occasional sexual reproduction is not excluded. Based on the whole-genome sequences alignment of 46 C. parasitica isolates from France, North America and Asia, genealogy and population structure analyses mostly confirmed these lineages as clonal. However, one of these clonal lineages showed a signal of strong recombination, suggesting different strategies of reproduction in western Europe. Signatures of several recent recombination events within all the French clonal lineages studied here were also identified, indicating that gene flow is regular between these lineages. In addition, haplotype identification of seven French clonal lineages revealed that emergences of new clonal lineages during colonization were the result of hybridization between the main expanding clonal lineages and minor haplotypes non-sequenced in the present study. This whole-genome sequencing study underlines the importance of recombination events in the invasive success of these clonal populations, and suggests that sexual reproduction may be more frequent within and between the western European clonal lineages of C. parasitica than previously assumed using few genetic markers.Copyright © 2019 Elsevier Inc. All rights reserved.

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April 21, 2020  |  

An African Salmonella Typhimurium ST313 sublineage with extensive drug-resistance and signatures of host adaptation.

Bloodstream infections by Salmonella enterica serovar Typhimurium constitute a major health burden in sub-Saharan Africa (SSA). These invasive non-typhoidal (iNTS) infections are dominated by isolates of the antibiotic resistance-associated sequence type (ST) 313. Here, we report emergence of ST313 sublineage II.1 in the Democratic Republic of the Congo. Sublineage II.1 exhibits extensive drug resistance, involving a combination of multidrug resistance, extended spectrum ß-lactamase production and azithromycin resistance. ST313 lineage II.1 isolates harbour an IncHI2 plasmid we name pSTm-ST313-II.1, with one isolate also exhibiting decreased ciprofloxacin susceptibility. Whole genome sequencing reveals that ST313 II.1 isolates have accumulated genetic signatures potentially associated with altered pathogenicity and host adaptation, related to changes observed in biofilm formation and metabolic capacity. Sublineage II.1 emerged at the beginning of the 21st century and is involved in on-going outbreaks. Our data provide evidence of further evolution within the ST313 clade associated with iNTS in SSA.

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April 21, 2020  |  

A genomic resource derived from the integration of genome sequences, expressed transcripts and genetic markers in ramie.

The redundancy of genomic resources, including transcript and molecular markers, and their uncertain position in the genome have dramatically hindered the study of traits in ramie, an important natural fiber crop.We obtained a high-quality transcriptome consisting of 30,591 non-redundant transcripts using single-molecule long-read sequencing and proposed it as a universal ramie transcriptome. Additionally, 55,882 single nucleotide polymorphisms (SNPs) were identified and a high-density genetic map was developed. Based on this genetic map, 181.7?Mb ramie genome sequences were assembled into 14 chromosomes. For the convenient use of these resources, 29,286 (~?95.7%) of the transcripts and all 55,882 SNPs, along with 1827 previously reported sequence repeat markers (SSRs), were mapped into the ramie genome, and 22,343 (~?73.0%) transcripts, 50,154 (~?89.7%) SNPs, and 1466 (~?80.3%) SSRs were assigned to a specific location in the corresponding chromosome.This is the first study to characterize the ramie transcriptome by long-read sequencing, and the substantial number of transcripts of significant length obtained will accelerate our understanding of ramie growth and development. This integration of genome sequences, expressed transcripts, and genetic markers will provide an extremely useful resource for genetic, molecular, and breeding studies of ramie.

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April 21, 2020  |  

Long-read sequencing reveals a 4.4 kb tandem repeat region in the mitogenome of Echinococcus granulosus (sensu stricto) genotype G1.

Echinococcus tapeworms cause a severe helminthic zoonosis called echinococcosis. The genus comprises various species and genotypes, of which E. granulosus (sensu stricto) represents a significant global public health and socioeconomic burden. Mitochondrial (mt) genomes have provided useful genetic markers to explore the nature and extent of genetic diversity within Echinococcus and have underpinned phylogenetic and population structure analyses of this genus. Our recent work indicated a sequence gap (>?1 kb) in the mt genomes of E. granulosus genotype G1, which could not be determined by PCR-based Sanger sequencing. The aim of the present study was to define the complete mt genome, irrespective of structural complexities, using a long-read sequencing method.We extracted high molecular weight genomic DNA from protoscoleces from a single cyst of E. granulosus genotype G1 from a sheep from Australia using a conventional method and sequenced it using PacBio Sequel (long-read) technology, complemented by BGISEQ-500 short-read sequencing. Sequence data obtained were assembled using a recently-developed workflow.We assembled a complete mt genome sequence of 17,675 bp, which is >?4 kb larger than the complete mt genomes known for E. granulosus genotype G1. This assembly includes a previously-elusive tandem repeat region, which is 4417 bp long and consists of ten near-identical 441-445 bp repeat units, each harbouring a 184 bp non-coding region and adjacent regions. We also identified a short non-coding region of 183 bp, which includes an inverted repeat.We report what we consider to be the first complete mt genome of E. granulosus genotype G1 and characterise all repeat regions in this genome. The numbers, sizes, sequences and functions of tandem repeat regions remain to be studied in different isolates of genotype G1 and in other genotypes and species. The discovery of such ‘new’ repeat elements in the mt genome of genotype G1 by PacBio sequencing raises a question about the completeness of some published genomes of taeniid cestodes assembled from conventional or short-read sequence datasets. This study shows that long-read sequencing readily overcomes the challenges of assembling repeat elements to achieve improved genomes.

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April 21, 2020  |  

Comparative genomic and phylogenetic analyses of Populus section Leuce using complete chloroplast genome sequences

Species of Populus section Leuce are distributed throughout most parts of the Northern Hemisphere and have important economic and ecological significance. However, due to frequent hybridization within Leuce, the phylogenetic relationship between species has not been clarified. The chloroplast (cp) genome is characterized by maternal inheritance and relatively conservative mutation rates; thus, it is a powerful tool for building phylogenetic trees. In this study, we used the PacBio SEQUEL software to determine that the cp genome of Populus tomentosa has a length of 156,558 bp including a long single-copy region (84,717 bp), a small single-copy region (16,555 bp), and a pair of inverted repeat regions (27,643 bp). The cp genome contains 131 unique genes, including 37 transfer RNAs, 8 ribosomal RNAs, and 86 protein-coding genes. We compared the cp genomes of seven species of section Leuce and identified five cp DNA markers with >?1% variable sites. Phylogenetic analyses revealed two evolutionary branches for section Leuce. The species with the closest relationship with P. tomenstosa was P. adenopoda, followed by P. alba. These cp genome data will help to determine the cp evolution of section Leuce and further elucidate the origin of P. tomentosa.

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