Insertion-deletion polymorphisms (indels) as genetic markers in natural populations

<p>Abstract</p> <p>Background</p> <p>We introduce the use of short insertion-deletion polymorphisms (indels) for genetic analysis of natural populations.</p> <p>Results</p> <p>Sequence reads from light shot-gun sequencing efforts of different dog breeds were aligned to the dog genome reference sequence and gaps corresponding to indels were identified. One hundred candidate markers (4-bp indels) were selected and genotyped in unrelated dogs (n = 7) and wolves (n = 18). Eighty-one and 76 out of 94 could be validated as polymorphic loci in the respective sample. Mean indel heterozygosity in a diverse set of wolves was 19%, and 74% of the loci had a minor allele frequency of >10%. Indels found to be polymorphic in wolves were subsequently genotyped in a highly bottlenecked Scandinavian wolf population. Fifty-one loci turned out to be polymorphic, showing their utility even in a population with low genetic diversity. In this population, individual heterozygosity measured at indel and microsatellite loci were highly correlated.</p> <p>Conclusion</p> <p>With an increasing amount of sequence information gathered from non-model organisms, we suggest that indels will come to form an important source of genetic markers, easy and cheap to genotype, for studies of natural populations.</p

Comparative genomics highlights the importance of drug efflux transporters during evolution of mycoparasitism in Clonostachys subgenus Bionectria (Fungi, Ascomycota, Hypocreales)

Various strains of the mycoparasitic fungal speciesClonostachys roseaare used commercially as biological control agents for the control of fungal plant diseases in agricultural crop production. Further improvements of the use and efficacy ofC. roseain biocontrol require a mechanistic understanding of the factors that determines the outcome of the interaction betweenC. roseaand plant pathogenic fungi. Here, we determined the genome sequences of 11Clonostachysstrains, representing five species inClonostachyssubgenusBionectria, and performed a comparative genomic analysis with the aim to identify gene families evolving under selection for gene gains or losses. Several gene families predicted to encode proteins involved in biosynthesis of secondary metabolites, including polyketide synthases, nonribosomal peptide syntethases and cytochrome P450s, evolved under selection for gene gains (p <= .05) in theBionectriasubgenus lineage. This was accompanied with gene copy number increases (p <= .05) in ATP-binding cassette (ABC) transporters and major facilitator superfamily (MFS) transporters predicted to contribute to drug efflux. MostClonostachysspecies were also characterized by high numbers of auxiliary activity (AA) family 9 lytic polysaccharide monooxygenases, AA3 glucose-methanol-choline oxidoreductases and additional carbohydrate-active enzyme gene families with putative activity (or binding) towards xylan and rhamnose/pectin substrates. Particular features of theC. roseagenome included expansions (p <= .05) of the ABC-B4 multidrug resistance transporters, the ABC-C5 multidrug resistance-related transporters and the 2.A.1.3 drug:H + antiporter-2 MFS drug resistance transporters. The ABC-G1 pleiotropic drug resistance transporter geneabcG6inC. roseawas induced (p <= .009) by exposure to the antifungalFusariummycotoxin zearalenone (1121-fold) and various fungicides. Deletion ofabcG6resulted in mutants with reduced (p < .001) growth rates on media containing the fungicides boscalid, fenhexamid and iprodione. Our results emphasize the role of biosynthesis of, and protection against, secondary metabolites inClonostachyssubgenusBionectria

Out in the Cold: Identification of Genomic Regions Associated With Cold Tolerance in the Biocontrol Fungus Clonostachys rosea Through Genome-Wide Association Mapping

There is an increasing importance for using biocontrol agents in combating plant diseases sustainably and in the long term. As large scale genomic sequencing becomes economically viable, the impact of single nucleotide polymorphisms (SNPs) on biocontrol-associated phenotypes can be easily studied across entire genomes of fungal populations. Here, we improved a previously reported genome assembly of the biocontrol fungus Clonostachys rosea strain IK726 using the PacBio sequencing platform, which resulted in a total genome size of 70.7 Mbp and 21,246 predicted genes. We further performed whole-genome re-sequencing of 52 additional C. rosea strains isolated globally using Illumina sequencing technology, in order to perform genome-wide association studies in conditions relevant for biocontrol activity. One such condition is the ability to grow at lower temperatures commonly encountered in cryic or frigid soils in temperate regions, as these will be prevalent for protecting growing crops in temperate climates. Growth rates at 10°C on potato dextrose agar of the 53 sequenced strains of C. rosea were measured and ranged between 0.066 and 0.413 mm/day. Performing a genome wide association study, a total of 1,478 SNP markers were significantly associated with the trait and located in 227 scaffolds, within or close to (&lt; 1000 bp distance) 265 different genes. The predicted gene products included several chaperone proteins, membrane transporters, lipases, and proteins involved in chitin metabolism with possible roles in cold tolerance. The data reported in this study provides a foundation for future investigations into the genetic basis for cold tolerance in fungi, with important implications for biocontrol

A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms

We describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms ( SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds ( a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines - in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases

The Genomic Landscape of Short Insertion and Deletion Polymorphisms in the Chicken (Gallus gallus) Genome: A High Frequency of Deletions in Tandem Duplicates

It is increasingly recognized that insertions and deletions (indels) are an important source of genetic as well as phenotypic divergence and diversity. We analyzed length polymorphisms identified through partial (0.25×) shotgun sequencing of three breeds of domestic chicken made by the International Chicken Polymorphism Map Consortium. A data set of 140,484 short indel polymorphisms in unique DNA was identified after filtering for microsatellite structures. There was a significant excess of tandem duplicates at indel sites, with deletions of a duplicate motif outnumbering the generation of duplicates through insertion. Indel density was lower in microchromosomes than in macrochromosomes, in the Z chromosome than in autosomes, and in 100 bp of upstream sequence, 5′-UTR, and first introns than in intergenic DNA and in other introns. Indel density was highly correlated with single nucleotide polymorphism (SNP) density. The mean density of indels in pairwise sequence comparisons was 1.9 × 10−4 indel events/bp, ∼5% the density of SNPs segregating in the chicken genome. The great majority of indels involved a limited number of nucleotides (median 1 bp), with A-rich motifs being overrepresented at indel sites. The overrepresentation of deletions at tandem duplicates indicates that replication slippage in duplicate sequences is a common mechanism behind indel mutation. The correlation between indel and SNP density indicates common effects of mutation and/or selection on the occurrence of indels and point mutations

Genome-wide analysis of microsatellite polymorphism in chicken circumventing the ascertainment bias

Studies of microsatellites evolution based on marker data almost inherently suffer from an ascertainment bias because there is selection for the most mutable and polymorphic loci during marker development. To circumvent this bias we took advantage of whole-genome shotgun sequence data from three unrelated chicken individuals that, when aligned to the genome reference sequence, give sequence information on two chromosomes from about one-fourth (375,000) of all microsatellite loci containing di- through pentanucleotide repeat motifs in the chicken genome. Polymorphism is seen at loci with as few as five repeat units, and the proportion of dimorphic loci then increases to 50% for sequences with ∼10 repeat units, to reach a maximum of 75%–80% for sequences with 15 or more repeat units. For any given repeat length, polymorphism increases with decreasing GC content of repeat motifs for dinucleotides, nonhairpin-forming trinucleotides, and tetranucleotides. For trinucleotide repeats which are likely to form hairpin structures, polymorphism increases with increasing GC content, indicating that the relative stability of hairpins affects the rate of replication slippage. For any given repeat length, polymorphism is significantly lower for imperfect compared to perfect repeats and repeat interruptions occur in >15% of loci. However, interruptions are not randomly distributed within repeat arrays but are preferentially located toward the ends. There is negative correlation between microsatellite abundance and single nucleotide polymorphism (SNP) density, providing large-scale genomic support for the hypothesis that equilibrium microsatellite distributions are governed by a balance between rate of replication slippage and rate of point mutation

Evidence for turnover of functional noncoding DNA in mammalian genome evolution.

The vast majority of the mammalian genome does not code for proteins, and a fundamental question in genomics is: What proportion of the noncoding mammalian genome is functional? Most attempts to address this issue use sequence comparisons between highly diverged mammals such as human and mouse to identify conservation due to negative selection. But such comparisons will underestimate the true proportion of functional noncoding DNA if there is turnover, if patterns of negative selection change over time. Here we test whether the inferred level of negative selection differs between different pairwise species comparisons. Using a multiple alignment of more than a megabase of contiguous sequence from eight mammalian species, we find a strong negative relationship between inferred levels of negative selection and pairwise divergence using 21 pairwise comparisons. This result suggests that there is a high rate of turnover of functional noncoding elements in the mammalian genome, so measures of functional constraint based on human–mouse comparisons may seriously underestimate the true value

Genetic Mapping in a Natural Population of Collared Flycatchers (Ficedula albicollis): Conserved Synteny but Gene Order Rearrangements on the Avian Z Chromosome

Data from completely sequenced genomes are likely to open the way for novel studies of the genetics of nonmodel organisms, in particular when it comes to the identification and analysis of genes responsible for traits that are under selection in natural populations. Here we use the draft sequence of the chicken genome as a starting point for linkage mapping in a wild bird species, the collared flycatcher—one of the most well-studied avian species in ecological and evolutionary research. A pedigree of 365 flycatchers was established and genotyped for single nucleotide polymorphisms in 23 genes selected from (and spread over most of) the chicken Z chromosome. All genes were also found to be located on the Z chromosome in the collared flycatcher, confirming conserved synteny at the level of gene content across distantly related avian lineages. This high degree of conservation mimics the situation seen for the mammalian X chromosome and may thus be a general feature in sex chromosome evolution, irrespective of whether there is male or female heterogamety. Alternatively, such unprecedented chromosomal conservation may be characteristic of most chromosomes in avian genome evolution. However, several internal rearrangements were observed, meaning that the transfer of map information from chicken to nonmodel bird species cannot always assume conserved gene orders. Interestingly, the rate of recombination on the Z chromosome of collared flycatchers was only ∼50% that of chicken, challenging the widely held view that birds generally have high recombination rates