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Vasoya D, Tzelos T, Benedictus L, Karagianni AE, Pirie S, Marr C, Oddsdóttir C, Fintl C, Connelley T. High-Resolution Genotyping of Expressed Equine MHC Reveals a Highly Complex MHC Structure. Genes (Basel) 2023; 14:1422. [PMID: 37510326 PMCID: PMC10379315 DOI: 10.3390/genes14071422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 06/29/2023] [Accepted: 07/04/2023] [Indexed: 07/30/2023] Open
Abstract
The Major Histocompatibility Complex (MHC) genes play a key role in a number of biological processes, most notably in immunological responses. The MHCI and MHCII genes incorporate a complex set of highly polymorphic and polygenic series of genes, which, due to the technical limitations of previously available technologies, have only been partially characterized in non-model but economically important species such as the horse. The advent of high-throughput sequencing platforms has provided new opportunities to develop methods to generate high-resolution sequencing data on a large scale and apply them to the analysis of complex gene sets such as the MHC. In this study, we developed and applied a MiSeq-based approach for the combined analysis of the expressed MHCI and MHCII repertoires in cohorts of Thoroughbred, Icelandic, and Norwegian Fjord Horses. The approach enabled us to generate comprehensive MHCI/II data for all of the individuals (n = 168) included in the study, identifying 152 and 117 novel MHCI and MHCII sequences, respectively. There was limited overlap in MHCI and MHCII haplotypes between the Thoroughbred and the Icelandic/Norwegian Fjord horses, showcasing the variation in MHC repertoire between genetically divergent breeds, and it can be inferred that there is much more MHC diversity in the global horse population. This study provided novel insights into the structure of the expressed equine MHC repertoire and highlighted unique features of the MHC in horses.
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Affiliation(s)
- Deepali Vasoya
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin EH25 9RG, UK
| | - Thomas Tzelos
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin EH25 9RG, UK
- Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ, UK
| | - Lindert Benedictus
- Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands
| | - Anna Eleonora Karagianni
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin EH25 9RG, UK
| | - Scott Pirie
- Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin EH25 9RG, UK
| | - Celia Marr
- Rossdales Equine Hospital, Cotton End Road, Exning, Newmarket CD8 7NN, UK
| | - Charlotta Oddsdóttir
- The Institute for Experimental Pathology at Keldur, University of Iceland Keldnavegur 3, 112 Reykjavík, Iceland
| | - Constanze Fintl
- Department of Companion Animal Clinical Sciences, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Timothy Connelley
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin EH25 9RG, UK
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Amo L, Amo de Paz G, Kabbert J, Machordom A. House sparrows do not exhibit a preference for the scent of potential partners with different MHC-I diversity and genetic distances. PLoS One 2022; 17:e0278892. [PMID: 36542616 PMCID: PMC9770374 DOI: 10.1371/journal.pone.0278892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 11/23/2022] [Indexed: 12/24/2022] Open
Abstract
MHC genes play a fundamental role in immune recognition of pathogens and parasites. Therefore, females may increase offspring heterozygosity and genetic diversity by selecting males with genetically compatible or heterozygous MHC. In birds, several studies suggest that MHC genes play a role in mate choice, and recent evidence suggests that olfaction may play a role in the MHC-II discrimination. However, whether olfaction is involved in MHC-I discrimination in birds remains unknown. Previous studies indicate that house sparrow females with low allelic diversity prefer males with higher diversity in MHC-I alleles. Here, we directly explored whether female and male house sparrows (Passer domesticus) could estimate by scent MHC-I diversity and/or dissimilarity of potential partners. Our results show that neither females nor males exhibit a preference related to MHC-I diversity or dissimilarity of potential partners, suggesting that MHC-I is not detected through olfaction. Further studies are needed to understand the mechanisms responsible for mate discrimination based on MHC-I in birds.
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Affiliation(s)
- Luisa Amo
- Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales (MNCN-CSIC), Madrid, Spain
- Area of Biodiversity and Conservation, Universidad Rey Juan Carlos, Móstoles, Spain
- * E-mail:
| | - Guillermo Amo de Paz
- Departamento de Farmacología, Farmacognosia y Botánica, Universidad Complutense de Madrid (UCM), Madrid, Spain
| | - Johanna Kabbert
- Department of Animal Behaviour, Bielefeld University, Bielefeld, Germany
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Annie Machordom
- Departamento de Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (MNCN-CSIC), Madrid, Spain
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3
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Råberg L, Clough D, Hagström Å, Scherman K, Andersson M, Drews A, Strandh M, Tschirren B, Westerdahl H. MHC class II genotype-by-pathogen genotype interaction for infection prevalence in a natural rodent-Borrelia system. Evolution 2022; 76:2067-2075. [PMID: 35909235 PMCID: PMC9541904 DOI: 10.1111/evo.14590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 05/25/2022] [Accepted: 07/11/2022] [Indexed: 01/22/2023]
Abstract
MHC genes are extraordinarily polymorphic in most taxa. Host-pathogen coevolution driven by negative frequency-dependent selection (NFDS) is one of the main hypotheses for the maintenance of such immunogenetic variation. Here, we test a critical but rarely tested assumption of this hypothesis-that MHC alleles affect resistance/susceptibility to a pathogen in a strain-specific way, that is, there is a host genotype-by-pathogen genotype interaction. In a field study of bank voles naturally infected with the tick-transmitted bacterium Borrelia afzelii, we tested for MHC class II (DQB) genotype-by-B. afzelii strain interactions for infection prevalence between 10 DQB alleles and seven strains. One allele (DQB*37) showed an interaction, such that voles carrying DQB*37 had higher prevalence of two strains and lower prevalence of one strain than individuals without the allele. These findings were corroborated by analyses of strain composition of infections, which revealed an effect of DQB*37 in the form of lower β diversity among infections in voles carrying the allele. Taken together, these results provide rare support at the molecular genetic level for a key assumption of models of antagonistic coevolution through NFDS.
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Affiliation(s)
- Lars Råberg
- Department of BiologyLund UniversityLundSE‐22362Sweden
| | - Dagmar Clough
- Department of BiologyLund UniversityLundSE‐22362Sweden
| | - Åsa Hagström
- Department of BiologyLund UniversityLundSE‐22362Sweden
| | | | | | - Anna Drews
- Department of BiologyLund UniversityLundSE‐22362Sweden
| | - Maria Strandh
- Department of BiologyLund UniversityLundSE‐22362Sweden
| | - Barbara Tschirren
- Department of BiologyLund UniversityLundSE‐22362Sweden,Centre for Ecology and ConservationUniversity of ExeterPenrynTR10 9FEUnited Kingdom
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4
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Scherman K, Råberg L, Westerdahl H. Borrelia Infection in Bank Voles Myodes glareolus Is Associated With Specific DQB Haplotypes Which Affect Allelic Divergence Within Individuals. Front Immunol 2021; 12:703025. [PMID: 34381454 PMCID: PMC8350566 DOI: 10.3389/fimmu.2021.703025] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 07/01/2021] [Indexed: 11/17/2022] Open
Abstract
The high polymorphism of Major Histocompatibility Complex (MHC) genes is generally considered to be a result of pathogen-mediated balancing selection. Such selection may operate in the form of heterozygote advantage, and/or through specific MHC allele–pathogen interactions. Specific MHC allele–pathogen interactions may promote polymorphism via negative frequency-dependent selection (NFDS), or selection that varies in time and/or space because of variability in the composition of the pathogen community (fluctuating selection; FS). In addition, divergent allele advantage (DAA) may act on top of these forms of balancing selection, explaining the high sequence divergence between MHC alleles. DAA has primarily been thought of as an extension of heterozygote advantage. However, DAA could also work in concert with NFDS though this is yet to be tested explicitly. To evaluate the importance of DAA in pathogen-mediated balancing selection, we surveyed allelic polymorphism of MHC class II DQB genes in wild bank voles (Myodes glareolus) and tested for associations between DQB haplotypes and infection by Borrelia afzelii, a tick-transmitted bacterium causing Lyme disease in humans. We found two significant associations between DQB haplotypes and infection status: one haplotype was associated with lower risk of infection (resistance), while another was associated with higher risk of infection (susceptibility). Interestingly, allelic divergence within individuals was higher for voles with the resistance haplotype compared to other voles. In contrast, allelic divergence was lower for voles with the susceptibility haplotype than other voles. The pattern of higher allelic divergence in individuals with the resistance haplotype is consistent with NFDS favouring divergent alleles in a natural population, hence selection where DAA works in concert with NFDS.
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Affiliation(s)
- Kristin Scherman
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
| | - Lars Råberg
- Functional Zoology, Department of Biology, Lund University, Lund, Sweden
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
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Kessler C, Brambilla A, Waldvogel D, Camenisch G, Biebach I, Leigh DM, Grossen C, Croll D. A robust sequencing assay of a thousand amplicons for the high-throughput population monitoring of Alpine ibex immunogenetics. Mol Ecol Resour 2021; 22:66-85. [PMID: 34152681 PMCID: PMC9292246 DOI: 10.1111/1755-0998.13452] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 06/10/2021] [Accepted: 06/14/2021] [Indexed: 11/27/2022]
Abstract
Polymorphism for immune functions can explain significant variation in health and reproductive success within species. Drastic loss in genetic diversity at such loci constitutes an extinction risk and should be monitored in species of conservation concern. However, effective implementations of genome‐wide immune polymorphism sets into high‐throughput genotyping assays are scarce. Here, we report the design and validation of a microfluidics‐based amplicon sequencing assay to comprehensively capture genetic variation in Alpine ibex (Capra ibex). This species represents one of the most successful large mammal restorations recovering from a severely depressed census size and a massive loss in diversity at the major histocompatibility complex (MHC). We analysed 65 whole‐genome sequencing sets of the Alpine ibex and related species to select the most representative markers and to prevent primer binding failures. In total, we designed ~1,000 amplicons densely covering the MHC, further immunity‐related genes as well as randomly selected genome‐wide markers for the assessment of neutral population structure. Our analysis of 158 individuals shows that the genome‐wide markers perform equally well at resolving population structure as RAD‐sequencing or low‐coverage genome sequencing data sets. Immunity‐related loci show unexpectedly high degrees of genetic differentiation within the species. Such information can now be used to define highly targeted individual translocations. Our design strategy can be realistically implemented into genetic surveys of a large range of species. In conclusion, leveraging whole‐genome sequencing data sets to design targeted amplicon assays allows the simultaneous monitoring of multiple genetic risk factors and can be translated into species conservation recommendations.
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Affiliation(s)
- Camille Kessler
- Laboratory of Evolutionary Genetics, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland
| | - Alice Brambilla
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.,Alpine Wildlife Research Center, Gran Paradiso National Park, Italy
| | - Dominique Waldvogel
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland
| | - Glauco Camenisch
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland
| | - Iris Biebach
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland
| | - Deborah M Leigh
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.,WSL Swiss Federal Research Institute, Birmensdorf, Switzerland
| | - Christine Grossen
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland
| | - Daniel Croll
- Laboratory of Evolutionary Genetics, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland
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6
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O'Connor EA, Westerdahl H. Trade-offs in expressed major histocompatibility complex diversity seen on a macroevolutionary scale among songbirds. Evolution 2021; 75:1061-1069. [PMID: 33666228 DOI: 10.1111/evo.14207] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 01/07/2021] [Accepted: 02/17/2021] [Indexed: 12/30/2022]
Abstract
To survive organisms must defend themselves against pathogens. Classical Major Histocompatibility Complex (MHC) genes play a key role in pathogen defense by encoding molecules involved in pathogen recognition. MHC gene diversity influences the variety of pathogens individuals can recognize and respond to and has consequently been a popular genetic marker for disease resistance in ecology and evolution. However, MHC diversity is predominantly estimated using genomic DNA (gDNA) with little knowledge of expressed diversity. This limits our ability to interpret the adaptive significance of variation in MHC diversity, especially in species with very many MHC genes such as songbirds. Here, we address this issue using phylogenetic comparative analyses of the number of MHC class I alleles (MHC-I diversity) in gDNA and complementary DNA (cDNA), that is, expressed alleles, across 13 songbird species. We propose three theoretical relationships that could be expected between genomic and expressed MHC-I diversity on a macroevolutionary scale and test which of these are best supported. In doing so, we show that significantly fewer MHC-I alleles than the number available are expressed, suggesting that optimal MHC-I diversity could be achieved by modulating gene expression. Understanding the relationship between genomic and expressed MHC diversity is essential for interpreting variation in MHC diversity in an evolutionary context.
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Affiliation(s)
- Emily A O'Connor
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
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Vavourakis CD, Heijnen L, Peters MCFM, Marang L, Ketelaars HAM, Hijnen WAM. Spatial and Temporal Dynamics in Attached and Suspended Bacterial Communities in Three Drinking Water Distribution Systems with Variable Biological Stability. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:14535-14546. [PMID: 33135888 DOI: 10.1021/acs.est.0c04532] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Microbial presence and regrowth in drinking water distribution systems (DWDSs) is routinely monitored to assess the biological stability of drinking water without a residual disinfectant, but the conventional microbiological culture methods currently used target only a very small fraction of the complete DWDS microbiome. Here, we sequenced 16S rRNA gene amplicons to elucidate the attached and suspended prokaryotic community dynamics within three nonchlorinated DWDSs with variable regrowth conditions distributing similarly treated surface water from the same source. One rural location, with less regrowth related issues, differed most strikingly from the other two urban locations by the exclusive presence of Pseudonocardia (Actinobacteria) in the biofilm and the absence of Limnobacter (Betaproteobacteriales) in the water and loose deposits during summer. There was a dominant seasonal effect on the drinking water microbiomes at all three locations. For one urban location, it was established that the most significant changes in the microbial community composition on a spatial scale occurred shortly after freshly treated water entered the DWDS. However, summerly regrowth of Limnobacter, one of the dominant genera in the distributed drinking water, already occurred in the clean water reservoir at the treatment plant before further distribution. The highlighted bacterial lineages within these highly diverse DWDS communities might be important new indicators for undesirable regrowth conditions affecting the final drinking water quality.
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Affiliation(s)
| | - Leo Heijnen
- KWR Watercycle Research Institute, Groningenhaven 7, 3433PE Nieuwegein, The Netherlands
| | | | - Leonie Marang
- Evides Water Company, P.O. Box 4472, 3006 AL, Rotterdam, The Netherlands
| | - Henk A M Ketelaars
- Evides Water Company, P.O. Box 4472, 3006 AL, Rotterdam, The Netherlands
| | - Wim A M Hijnen
- Evides Water Company, P.O. Box 4472, 3006 AL, Rotterdam, The Netherlands
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Hanson HE, Mathews NS, Hauber ME, Martin LB. The house sparrow in the service of basic and applied biology. eLife 2020; 9:e52803. [PMID: 32343224 PMCID: PMC7189751 DOI: 10.7554/elife.52803] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 04/06/2020] [Indexed: 12/13/2022] Open
Abstract
From the northernmost tip of Scandinavia to the southernmost corner of Patagonia, and across six continents, house sparrows (Passer domesticus) inhabit most human-modified habitats of the globe. With over 7,000 articles published, the species has become a workhorse for not only the study of self-urbanized wildlife, but also for understanding life history and body size evolution, sexual selection and many other biological phenomena. Traditionally, house sparrows were studied for their adaptations to local biotic and climatic conditions, but more recently, the species has come to serve as a focus for studies seeking to reveal the genomic, epigenetic and physiological underpinnings of success among invasive vertebrate species. Here, we review the natural history of house sparrows, highlight what the study of these birds has meant to bioscience generally, and describe the many resources available for future work on this species.
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Affiliation(s)
- Haley E Hanson
- Global and Planetary Health, University of South FloridaTampaUnited States
| | - Noreen S Mathews
- Global and Planetary Health, University of South FloridaTampaUnited States
| | - Mark E Hauber
- Department of Evolution, Ecology, and BehaviorUniversity of Illinois at Urbana-ChampaignUrbanaUnited States
| | - Lynn B Martin
- Global and Planetary Health, University of South FloridaTampaUnited States
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Donaldson ME, Jackson K, Rico Y, Sayers JB, Ethier DM, Kyle CJ. Development of a massively parallel, genotyping-by-sequencing assay in American badger (Taxidea taxus) highlights the need for careful validation when working with low template DNA. CONSERV GENET RESOUR 2020. [DOI: 10.1007/s12686-020-01146-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Nie H, Mansfield BC, Harre NT, Young JM, Steppig NR, Young BG. Investigating target-site resistance mechanism to the PPO-inhibiting herbicide fomesafen in waterhemp and interspecific hybridization of Amaranthus species using next generation sequencing. PEST MANAGEMENT SCIENCE 2019; 75:3235-3244. [PMID: 30983048 DOI: 10.1002/ps.5445] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Revised: 04/07/2019] [Accepted: 04/14/2019] [Indexed: 06/09/2023]
Abstract
BACKGROUND Waterhemp (Amaranthus tuberculatus (Moq.) J. D. Sauer) is one of the most pernicious weeds in cropping systems of the USA due to its evolved resistance against several herbicide sites-of-action, including protoporphyrinogen oxidase inhibitors (PPO-R). Currently, the only source of PPO-R documented in waterhemp is ΔG210 of PPX2. Gene flow may not only lead to a transfer of herbicide-resistant alleles, but also produce a hybrid genotype more competitively fit than one or both parents. However, investigating gene flow of Amaranthus species has been of interest in the past two decades with limited evidence. RESULTS Here, a high-throughput MiSeq amplicon sequencing method was used to investigate alterations of the PPX2 gene in 146 PPO-R waterhemp populations across five Midwest states of the USA. Five R128 codons of PPX2, novel to waterhemp, were found including AGG (R), GGA (G), GGG (G), AAA (K) and ATA (I). R128G, R128I, and R128K were found in 11, 3, and 2 populations, respectively. R128G and R128I, but not R128K, conferred fomesafen resistance in a bacterial system. Sequence alignment of the R128 region of PPX2 identified a tumble pigweed (Amaranthus albus)-type and Palmer amaranth (Amaranthus palmeri)-type PPX2 allele to be present and widespread in the surveyed waterhemp populations, thus providing strong evidence of gene flow between Amaranthus species. CONCLUSION Using a next-generation sequencing method, we identified two PPO target-site mutations R128G/I novel to waterhemp and provided evidence of gene flow of Amaranthus species in a large group of screened waterhemp populations from five Midwest states of the USA. © 2019 Society of Chemical Industry.
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Affiliation(s)
- Haozhen Nie
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - Brent C Mansfield
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - Nick T Harre
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - Julie M Young
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - Nicholas R Steppig
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - Bryan G Young
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
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Rekdal SL, Anmarkrud JA, Johnsen A, Lifjeld JT. Genotyping strategy matters when analyzing hypervariable major histocompatibility complex-Experience from a passerine bird. Ecol Evol 2018; 8:1680-1692. [PMID: 29435243 PMCID: PMC5792522 DOI: 10.1002/ece3.3757] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 11/30/2017] [Accepted: 12/04/2017] [Indexed: 12/26/2022] Open
Abstract
Genotyping of classical major histocompatibility complex (MHC) genes is challenging when they are hypervariable and occur in multiple copies. In this study, we used several different approaches to genotype the moderately variable MHC class I exon 3 (MHCIe3) and the highly polymorphic MHC class II exon 2 (MHCIIβe2) in the bluethroat (Luscinia svecica). Two family groups (eight individuals) were sequenced in replicates at both markers using Ion Torrent technology with both a single- and a dual-indexed primer structure. Additionally, MHCIIβe2 was sequenced on Illumina MiSeq. Allele calling was conducted by modifications of the pipeline developed by Sommer et al. (BMC Genomics, 14, 2013, 542) and the software AmpliSAS. While the different genotyping strategies gave largely consistent results for MHCIe3, with a maximum of eight alleles per individual, MHCIIβe2 was remarkably complex with a maximum of 56 MHCIIβe2 alleles called for one individual. Each genotyping strategy detected on average 50%-82% of all MHCIIβe2 alleles per individual, but dropouts were largely allele-specific and consistent within families for each strategy. The discrepancies among approaches indicate PCR biases caused by the platform-specific primer tails. Further, AmpliSAS called fewer alleles than the modified Sommer pipeline. Our results demonstrate that allelic dropout is a significant problem when genotyping the hypervariable MHCIIβe2. As these genotyping errors are largely nonrandom and method-specific, we caution against comparing genotypes across different genotyping strategies. Nevertheless, we conclude that high-throughput approaches provide a major advance in the challenging task of genotyping hypervariable MHC loci, even though they may not reveal the complete allelic repertoire.
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