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Fouks B, Miller KJ, Ross C, Jones C, Rueppell O. Alternative double strand break repair pathways shape the evolution of high recombination in the honey bee, Apis mellifera. INSECT MOLECULAR BIOLOGY 2025; 34:185-202. [PMID: 39297191 PMCID: PMC11705527 DOI: 10.1111/imb.12961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Accepted: 09/02/2024] [Indexed: 01/11/2025]
Abstract
Social insects, particularly honey bees, have exceptionally high genomic frequencies of genetic recombination. This phenomenon and underlying mechanisms are poorly understood. To characterise the patterns of crossovers and gene conversion in the honey bee genome, a recombination map of 187 honey bee brothers was generated by whole-genome resequencing. Recombination events were heterogeneously distributed without many true hotspots. The tract lengths between phase shifts were bimodally distributed, indicating distinct crossover and gene conversion events. While crossovers predominantly occurred in G/C-rich regions and seemed to cause G/C enrichment, the gene conversions were found predominantly in A/T-rich regions. The nucleotide composition of sequences involved in gene conversions that were associated with or distant from crossovers corresponded to the differences between crossovers and gene conversions. These combined results suggest two types of DNA double-strand break repair during honey bee meiosis: non-canonical homologous recombination, leading to gene conversion and A/T enrichment of the genome, and the canonical homologous recombination based on completed double Holliday Junctions, which can result in gene conversion or crossover and is associated with G/C bias. This G/C bias may be selected for to balance the A/T-rich base composition of eusocial hymenopteran genomes. The lack of evidence for a preference of the canonical homologous recombination for double-strand break repair suggests that the high genomic recombination rate of honey bees is mainly the consequence of a high rate of double-strand breaks, which could in turn result from the life history of honey bees and their A/T-rich genome.
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Affiliation(s)
- Bertrand Fouks
- Department of BiologyUniversity of North Carolina at GreensboroGreensboroNorth CarolinaUSA
- UMR AGAP Institut, Univ Montpellier, CIRAD, INRAE, Institut AgroMontpellierFrance
- CIRAD, UMR AGAP InstitutMontpellierFrance
| | - Katelyn J. Miller
- Department of BiologyUniversity of North Carolina at GreensboroGreensboroNorth CarolinaUSA
- Smithers PDSGaithersburgMarylandUSA
| | - Caitlin Ross
- Department of Computer SciencesUniversity of North Carolina at GreensboroGreensboroNorth CarolinaUSA
- KitwareMinneapolisMinnesotaUSA
| | - Corbin Jones
- Department of BiologyUniversity of North Carolina at Chapel Hill & Carolina Center for Genome SciencesChapel HillNorth CarolinaUSA
| | - Olav Rueppell
- Department of BiologyUniversity of North Carolina at GreensboroGreensboroNorth CarolinaUSA
- Department of Biological SciencesUniversity of AlbertaEdmontonAlbertaCanada
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Zong X, Lou Y, Xia M, Zhao K, Chen J, Huang J, Yang S, Wang L. Recombination and repeat-induced point mutation landscapes reveal trade-offs between the sexual and asexual cycles of Magnaporthe oryzae. J Genet Genomics 2024; 51:723-734. [PMID: 38490361 DOI: 10.1016/j.jgg.2024.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 03/01/2024] [Accepted: 03/06/2024] [Indexed: 03/17/2024]
Abstract
The fungal disease caused by Magnaporthe oryzae is one of the most devastating diseases that endanger many crops worldwide. Evidence shows that sexual reproduction can be advantageous for fungal diseases as hybridization facilitates host-jumping. However, the pervasive clonal lineages of M. oryzae observed in natural fields contradict this expectation. A better understanding of the roles of recombination and the fungi-specific repeat-induced point mutation (RIP) in shaping its evolutionary trajectory is essential to bridge this knowledge gap. Here we systematically investigate the RIP and recombination landscapes in M. oryzae using a whole genome sequencing data from 252 population samples and 92 cross progenies. Our data reveal that the RIP can robustly capture the population history of M. oryzae, and we provide accurate estimations of the recombination and RIP rates across different M. oryzae clades. Significantly, our results highlight a parent-of-origin bias in both recombination and RIP rates, tightly associating with their sexual potential and variations of effector proteins. This bias suggests a critical trade-off between generating novel allelic combinations in the sexual cycle to facilitate host-jumping and stimulating transposon-associated diversification of effectors in the asexual cycle to facilitate host coevolution. These findings provide unique insights into understanding the evolution of blast fungus.
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Affiliation(s)
- Xifang Zong
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China
| | - Yaxin Lou
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China
| | - Mengshuang Xia
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China
| | - Kunyang Zhao
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China
| | - Jingxuan Chen
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China
| | - Ju Huang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, Bioinformatics Center, Academy for Advanced Interdisciplinary Studies, Nanjing Agricultural University, Nanjing, Jiangsu 210000, China
| | - Sihai Yang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China; Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing, Jiangsu 210000, China.
| | - Long Wang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210000, China.
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Fernandes JB, Naish M, Lian Q, Burns R, Tock AJ, Rabanal FA, Wlodzimierz P, Habring A, Nicholas RE, Weigel D, Mercier R, Henderson IR. Structural variation and DNA methylation shape the centromere-proximal meiotic crossover landscape in Arabidopsis. Genome Biol 2024; 25:30. [PMID: 38254210 PMCID: PMC10804481 DOI: 10.1186/s13059-024-03163-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 01/01/2024] [Indexed: 01/24/2024] Open
Abstract
BACKGROUND Centromeres load kinetochore complexes onto chromosomes, which mediate spindle attachment and allow segregation during cell division. Although centromeres perform a conserved cellular function, their underlying DNA sequences are highly divergent within and between species. Despite variability in DNA sequence, centromeres are also universally suppressed for meiotic crossover recombination, across eukaryotes. However, the genetic and epigenetic factors responsible for suppression of centromeric crossovers remain to be completely defined. RESULTS To explore the centromere-proximal meiotic recombination landscape, we map 14,397 crossovers against fully assembled Arabidopsis thaliana (A. thaliana) genomes. A. thaliana centromeres comprise megabase satellite repeat arrays that load nucleosomes containing the CENH3 histone variant. Each chromosome contains a structurally polymorphic region of ~3-4 megabases, which lack crossovers and include the satellite arrays. This polymorphic region is flanked by ~1-2 megabase low-recombination zones. These recombination-suppressed regions are enriched for Gypsy/Ty3 retrotransposons, and additionally contain expressed genes with high genetic diversity that initiate meiotic recombination, yet do not crossover. We map crossovers at high-resolution in proximity to CEN3, which resolves punctate centromere-proximal hotspots that overlap gene islands embedded in heterochromatin. Centromeres are densely DNA methylated and the recombination landscape is remodelled in DNA methylation mutants. We observe that the centromeric low-recombining zones decrease and increase crossovers in CG (met1) and non-CG (cmt3) mutants, respectively, whereas the core non-recombining zones remain suppressed. CONCLUSION Our work relates the genetic and epigenetic organization of A. thaliana centromeres and flanking pericentromeric heterochromatin to the zones of crossover suppression that surround the CENH3-occupied satellite repeat arrays.
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Affiliation(s)
- Joiselle B Fernandes
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, D-50829, Cologne, Germany
| | - Matthew Naish
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Qichao Lian
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, D-50829, Cologne, Germany
| | - Robin Burns
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Andrew J Tock
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Fernando A Rabanal
- Department of Molecular Biology, Max Planck Institute for Biology, Tübingen, D-72076, Tübingen, Germany
| | - Piotr Wlodzimierz
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Anette Habring
- Department of Molecular Biology, Max Planck Institute for Biology, Tübingen, D-72076, Tübingen, Germany
| | - Robert E Nicholas
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Detlef Weigel
- Department of Molecular Biology, Max Planck Institute for Biology, Tübingen, D-72076, Tübingen, Germany
- University of Tübingen, Institute for Bioinformatics and Medical Informatics, D-72076, Tübingen, Germany
| | - Raphael Mercier
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, D-50829, Cologne, Germany
| | - Ian R Henderson
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK.
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Abstract
Introducing asexual reproduction through seeds - apomixis - into crop species could revolutionize agriculture by allowing F1 hybrids with enhanced yield and stability to be clonally propagated. Engineering synthetic apomixis has proven feasible in inbred rice through the inactivation of three genes (MiMe), which results in the conversion of meiosis into mitosis in a line ectopically expressing the BABYBOOM1 (BBM1) parthenogenetic trigger in egg cells. However, only 10-30% of the seeds are clonal. Here, we show that synthetic apomixis can be achieved in an F1 hybrid of rice by inducing MiMe mutations and egg cell expression of BBM1 in a single step. We generate hybrid plants that produce more than 95% of clonal seeds across multiple generations. Clonal apomictic plants maintain the phenotype of the F1 hybrid along successive generations. Our results demonstrate that there is no barrier to almost fully penetrant synthetic apomixis in an important crop species, rendering it compatible with use in agriculture.
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Joint control of meiotic crossover patterning by the synaptonemal complex and HEI10 dosage. Nat Commun 2022; 13:5999. [PMID: 36224180 PMCID: PMC9556546 DOI: 10.1038/s41467-022-33472-w] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 09/19/2022] [Indexed: 11/09/2022] Open
Abstract
Meiotic crossovers are limited in number and are prevented from occurring close to each other by crossover interference. In many species, crossover number is subject to sexual dimorphism, and a lower crossover number is associated with shorter chromosome axes lengths. How this patterning is imposed remains poorly understood. Here, we show that overexpression of the Arabidopsis pro-crossover protein HEI10 increases crossovers but maintains some interference and sexual dimorphism. Disrupting the synaptonemal complex by mutating ZYP1 also leads to an increase in crossovers but, in contrast, abolishes interference and disrupts the link between chromosome axis length and crossovers. Crucially, combining HEI10 overexpression and zyp1 mutation leads to a massive and unprecedented increase in crossovers. These observations support and can be predicted by, a recently proposed model in which HEI10 diffusion along the synaptonemal complex drives a coarsening process leading to well-spaced crossover-promoting foci, providing a mechanism for crossover patterning. During meiosis, the number and distribution of crossovers (COs) are tightly controlled, but the mechanistic basis of this control is unclear. Here, by combining experimental data and mathematical modeling, the study advocates a CO patterning model via coarsening through the diffusion of HEI10 along the synaptonemal complex.
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Sharma K, Iruegas-Bocardo F, Abdurahman A, Alcalá-Briseño RI, Garrett KA, Goss EM, Ngundo G, Kreuze J, Atieno E, Munguti F. Ralstonia Strains from Potato-Growing Regions of Kenya Reveal Two Phylotypes and Epidemic Clonality of Phylotype II Sequevar 1 Strains. PHYTOPATHOLOGY 2022; 112:1640-1650. [PMID: 35522048 DOI: 10.1094/phyto-08-21-0339-r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Bacterial wilt, caused by the Ralstonia solanacearum species complex (RSSC), is the most destructive potato disease in Kenya. Studies were conducted to (i) determine the molecular diversity of RSSC strains associated with bacterial wilt of potato in Kenya, (ii) generate an RSSC distribution map for epidemiological inference, and (iii) determine whether phylotype II sequevar 1 strains exhibit epidemic clonality. Surveys were conducted in 2018 and 2019, in which tubers from wilting potato plants and stem samples of potential alternative hosts were collected for pathogen isolation. The pathogen was phylotyped by multiplex PCR and 536 RSSC strains typed at a sequevar level. Two RSSC phylotypes were identified, phylotype II (98.4%, n = 506 [sequevar 1 (n = 505) and sequevar 2 (n = 1)]) and phylotype I (1.6%, n = 30 [sequevar 13 (n = 9) and a new sequevar (n = 21)]). The phylotype II sequevar 1 strains were haplotyped using multilocus tandem repeat sequence typing (TRST) schemes. The TRST scheme identified 51 TRST profiles within the phylotype II sequevar 1 strains with a modest diversity index (HGDI = 0.87), confirming the epidemic clonality of RSSC phylotype II sequevar 1 strains in Kenya. A minimum spanning tree and mapping of the TRST profiles revealed that TRST27 '8-5-12-7-5' is the primary founder of the clonal complex of RSSC phylotype II sequevar 1 and is widely distributed via latently infected seed tubers. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
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Affiliation(s)
- Kalpana Sharma
- Consultative Group for International Agricultural Research (CGIAR) Research Program on Roots, Tubers and Bananas (RTB), Centro Internacional de la Papa, Nairobi, Kenya, Lima, Peru
- International Potato Center (CIP), Sub-Saharan Africa Regional Office, Nairobi, Kenya
| | | | - Abdulwahab Abdurahman
- Consultative Group for International Agricultural Research (CGIAR) Research Program on Roots, Tubers and Bananas (RTB), Centro Internacional de la Papa, Nairobi, Kenya, Lima, Peru
- International Potato Center (CIP), Sub-Saharan Africa Regional Office, Nairobi, Kenya
| | - Ricardo I Alcalá-Briseño
- Plant Pathology Department, University of Florida, Gainesville, FL, U.S.A
- Emerging Pathogens Institute, University of Florida, Gainesville, FL, U.S.A
- Food Systems Institute, University of Florida, Gainesville, FL, U.S.A
| | - Karen A Garrett
- Plant Pathology Department, University of Florida, Gainesville, FL, U.S.A
- Emerging Pathogens Institute, University of Florida, Gainesville, FL, U.S.A
- Food Systems Institute, University of Florida, Gainesville, FL, U.S.A
| | - Erica M Goss
- Plant Pathology Department, University of Florida, Gainesville, FL, U.S.A
- Emerging Pathogens Institute, University of Florida, Gainesville, FL, U.S.A
| | - George Ngundo
- Kenya Plant Health Inspectorate Service (KEPHIS), Plant Quarantine and Biosecurity Station (PQBS), Nairobi, Kenya
| | - Jan Kreuze
- Consultative Group for International Agricultural Research (CGIAR) Research Program on Roots, Tubers and Bananas (RTB), Centro Internacional de la Papa, Nairobi, Kenya, Lima, Peru
- International Potato Center (CIP), Crop and Systems Sciences Division, Lima, Peru
| | - Elly Atieno
- Consultative Group for International Agricultural Research (CGIAR) Research Program on Roots, Tubers and Bananas (RTB), Centro Internacional de la Papa, Nairobi, Kenya, Lima, Peru
- International Potato Center (CIP), Sub-Saharan Africa Regional Office, Nairobi, Kenya
| | - Florence Munguti
- Kenya Plant Health Inspectorate Service (KEPHIS), Plant Quarantine and Biosecurity Station (PQBS), Nairobi, Kenya
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Lian Q, Solier V, Walkemeier B, Durand S, Huettel B, Schneeberger K, Mercier R. The megabase-scale crossover landscape is largely independent of sequence divergence. Nat Commun 2022; 13:3828. [PMID: 35780220 PMCID: PMC9250513 DOI: 10.1038/s41467-022-31509-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 06/20/2022] [Indexed: 02/01/2023] Open
Abstract
Meiotic recombination frequency varies along chromosomes and strongly correlates with sequence divergence. However, the causal relationship between recombination landscapes and polymorphisms is unclear. Here, we characterize the genome-wide recombination landscape in the quasi-absence of polymorphisms, using Arabidopsis thaliana homozygous inbred lines in which a few hundred genetic markers were introduced through mutagenesis. We find that megabase-scale recombination landscapes in inbred lines are strikingly similar to the recombination landscapes in hybrids, with the notable exception of heterozygous large rearrangements where recombination is prevented locally. In addition, the megabase-scale recombination landscape can be largely explained by chromatin features. Our results show that polymorphisms are not a major determinant of the shape of the megabase-scale recombination landscape but rather favour alternative models in which recombination and chromatin shape sequence divergence across the genome. The frequency of recombination varies along chromosomes and highly correlates with sequence divergence. Here, the authors show that polymorphisms are not a major determinant of the megabase-scale recombination landscape in Arabidopsis, which is rather determined by chromatin accessibility and DNA methylation.
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Affiliation(s)
- Qichao Lian
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Victor Solier
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Birgit Walkemeier
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Stéphanie Durand
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Bruno Huettel
- Max Planck-Genome-centre Cologne, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Korbinian Schneeberger
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany. .,Faculty of Biology, LMU Munich, 82152, Planegg-Martinsried, Germany.
| | - Raphael Mercier
- Department of Chromosome Biology, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany.
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Lian Q, Chen Y, Chang F, Fu Y, Qi J. inGAP-family: Accurate Detection of Meiotic Recombination Loci and Causal Mutations by Filtering Out Artificial Variants due to Genome Complexities. GENOMICS, PROTEOMICS & BIOINFORMATICS 2022; 20:524-535. [PMID: 33711466 PMCID: PMC9801030 DOI: 10.1016/j.gpb.2019.11.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 09/04/2019] [Accepted: 11/08/2019] [Indexed: 01/26/2023]
Abstract
Accurately identifying DNA polymorphisms can bridge the gap between phenotypes and genotypes and is essential for molecular marker assisted genetic studies. Genome complexities, including large-scale structural variations, bring great challenges to bioinformatic analysis for obtaining high-confidence genomic variants, as sequence differences between non-allelic loci of two or more genomes can be misinterpreted as polymorphisms. It is important to correctly filter out artificial variants to avoid false genotyping or estimation of allele frequencies. Here, we present an efficient and effective framework, inGAP-family, to discover, filter, and visualize DNA polymorphisms and structural variants (SVs) from alignment of short reads. Applying this method to polymorphism detection on real datasets shows that elimination of artificial variants greatly facilitates the precise identification of meiotic recombination points as well as causal mutations in mutant genomes or quantitative trait loci. In addition, inGAP-family provides a user-friendly graphical interface for detecting polymorphisms and SVs, further evaluating predicted variants and identifying mutations related to genotypes. It is accessible at https://sourceforge.net/projects/ingap-family/.
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A complete, telomere-to-telomere human genome sequence presents new opportunities for evolutionary genomics. Nat Methods 2022; 19:635-638. [PMID: 35689027 DOI: 10.1038/s41592-022-01512-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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10
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Li J, Llorente B, Liti G, Yue JX. RecombineX: A generalized computational framework for automatic high-throughput gamete genotyping and tetrad-based recombination analysis. PLoS Genet 2022; 18:e1010047. [PMID: 35533184 PMCID: PMC9119626 DOI: 10.1371/journal.pgen.1010047] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Revised: 05/19/2022] [Accepted: 04/14/2022] [Indexed: 01/09/2023] Open
Abstract
Meiotic recombination is an essential biological process that ensures faithful chromosome segregation and promotes parental allele shuffling. Tetrad analysis is a powerful approach to quantify the genetic makeups and recombination landscapes of meiotic products. Here we present RecombineX (https://github.com/yjx1217/RecombineX), a generalized computational framework that automates the full workflow of marker identification, gamete genotyping, and tetrad-based recombination profiling based on any organism or genetic background with batch processing capability. Aside from conventional reference-based analysis, RecombineX can also perform analysis based on parental genome assemblies, which facilitates analyzing meiotic recombination landscapes in their native genomic contexts. Additional features such as copy number variation profiling and missing genotype inference further enhance downstream analysis. RecombineX also includes a dedicate module for simulating the genomes and reads of recombinant tetrads, which enables fine-tuned simulation-based hypothesis testing. This simulation module revealed the power and accuracy of RecombineX even when analyzing tetrads with very low sequencing depths (e.g., 1-2X). Tetrad sequencing data from the budding yeast Saccharomyces cerevisiae and green alga Chlamydomonas reinhardtii were further used to demonstrate the accuracy and robustness of RecombineX for organisms with both small and large genomes, manifesting RecombineX as an all-around one stop solution for future tetrad analysis. Interestingly, our re-analysis of the budding yeast tetrad sequencing data with RecombineX and Oxford Nanopore sequencing revealed two unusual structural rearrangement events that were not noticed before, which exemplify the occasional genome instability triggered by meiosis.
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Affiliation(s)
- Jing Li
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat-sen University Cancer Center, Guangzhou, China
- Université Côte d’Azur, CNRS, INSERM, IRCAN, Nice, France
| | - Bertrand Llorente
- Aix-Marseille Université, CNRS, INSERM, CRCM, Institut Paoli-Calmettes, Marseille, France
| | - Gianni Liti
- Université Côte d’Azur, CNRS, INSERM, IRCAN, Nice, France
- * E-mail: (GL); (JXY)
| | - Jia-Xing Yue
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat-sen University Cancer Center, Guangzhou, China
- Université Côte d’Azur, CNRS, INSERM, IRCAN, Nice, France
- * E-mail: (GL); (JXY)
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The synaptonemal complex imposes crossover interference and heterochiasmy in Arabidopsis. Proc Natl Acad Sci U S A 2021; 118:2023613118. [PMID: 33723072 PMCID: PMC8000504 DOI: 10.1073/pnas.2023613118] [Citation(s) in RCA: 106] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Meiotic recombination promotes genetic diversity by shuffling parental chromosomes. As observed by the very first geneticists, crossovers inhibit the formation of another crossover nearby, an elusive phenomenon called crossover interference. Another intriguing observation is heterochiasmy, the marked difference in male and female crossover rates observed in many species. Here, we show that the synaptonemal complex, a structure that zips homologous chromosomes together during meiosis, is essential for crossover interference in Arabidopsis. This suggests that a signal that inhibits crossover formation nearby a first crossover propagates along this specific structure. Furthermore, in the absence of the synaptonemal complex, crossover frequencies become identical in both sexes, suggesting that heterochiasmy is due to variation of crossover interference imposed by the synaptonemal complex. Meiotic crossovers (COs) have intriguing patterning properties, including CO interference, the tendency of COs to be well-spaced along chromosomes, and heterochiasmy, the marked difference in male and female CO rates. During meiosis, transverse filaments transiently associate the axes of homologous chromosomes, a process called synapsis that is essential for CO formation in many eukaryotes. Here, we describe the spatial organization of the transverse filaments in Arabidopsis (ZYP1) and show it to be evolutionary conserved. We show that in the absence of ZYP1 (zyp1a zyp1b null mutants), chromosomes associate in pairs but do not synapse. Unexpectedly, in absence of ZYP1, CO formation is not prevented but increased. Furthermore, genome-wide analysis of recombination revealed that CO interference is abolished, with the frequent observation of close COs. In addition, heterochiasmy was erased, with identical CO rates in males and females. This shows that the tripartite synaptonemal complex is dispensable for CO formation and has a key role in regulating their number and distribution, imposing CO interference and heterochiasmy.
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12
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Cheng YH, Liu CFJ, Yu YH, Jhou YT, Fujishima M, Tsai IJ, Leu JY. Genome plasticity in Paramecium bursaria revealed by population genomics. BMC Biol 2020; 18:180. [PMID: 33250052 PMCID: PMC7702705 DOI: 10.1186/s12915-020-00912-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 10/29/2020] [Indexed: 11/25/2022] Open
Abstract
Background Ciliates are an ancient and diverse eukaryotic group found in various environments. A unique feature of ciliates is their nuclear dimorphism, by which two types of nuclei, the diploid germline micronucleus (MIC) and polyploidy somatic macronucleus (MAC), are present in the same cytoplasm and serve different functions. During each sexual cycle, ciliates develop a new macronucleus in which newly fused genomes are extensively rearranged to generate functional minichromosomes. Interestingly, each ciliate species seems to have its way of processing genomes, providing a diversity of resources for studying genome plasticity and its regulation. Here, we sequenced and analyzed the macronuclear genome of different strains of Paramecium bursaria, a highly divergent species of the genus Paramecium which can stably establish endosymbioses with green algae. Results We assembled a high-quality macronuclear genome of P. bursaria and further refined genome annotation by comparing population genomic data. We identified several species-specific expansions in protein families and gene lineages that are potentially associated with endosymbiosis. Moreover, we observed an intensive chromosome breakage pattern that occurred during or shortly after sexual reproduction and contributed to highly variable gene dosage throughout the genome. However, patterns of copy number variation were highly correlated among genetically divergent strains, suggesting that copy number is adjusted by some regulatory mechanisms or natural selection. Further analysis showed that genes with low copy number variation among populations tended to function in basic cellular pathways, whereas highly variable genes were enriched in environmental response pathways. Conclusions We report programmed DNA rearrangements in the P. bursaria macronuclear genome that allow cells to adjust gene copy number globally according to individual gene functions. Our results suggest that large-scale gene copy number variation may represent an ancient mechanism for cells to adapt to different environments. Supplementary information The online version contains supplementary material available at 10.1186/s12915-020-00912-2.
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Affiliation(s)
- Yu-Hsuan Cheng
- Genome and Systems Biology Degree Program, Academia Sinica and National Taiwan University, Taipei, 106, Taiwan.,Institute of Molecular Biology, Academia Sinica, 128 Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan
| | - Chien-Fu Jeff Liu
- Institute of Molecular Biology, Academia Sinica, 128 Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan
| | - Yen-Hsin Yu
- Institute of Molecular Biology, Academia Sinica, 128 Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan
| | - Yu-Ting Jhou
- Institute of Molecular Biology, Academia Sinica, 128 Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan
| | - Masahiro Fujishima
- Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi, 753-8512, Japan
| | - Isheng Jason Tsai
- Genome and Systems Biology Degree Program, Academia Sinica and National Taiwan University, Taipei, 106, Taiwan.,Biodiversity Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Jun-Yi Leu
- Genome and Systems Biology Degree Program, Academia Sinica and National Taiwan University, Taipei, 106, Taiwan. .,Institute of Molecular Biology, Academia Sinica, 128 Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan.
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13
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Wang H, Xu W, Sun Y, Lian Q, Wang C, Yu C, He C, Wang J, Ma H, Copenhaver GP, Wang Y. The cohesin loader SCC2 contains a PHD finger that is required for meiosis in land plants. PLoS Genet 2020; 16:e1008849. [PMID: 32516352 PMCID: PMC7304647 DOI: 10.1371/journal.pgen.1008849] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 06/19/2020] [Accepted: 05/11/2020] [Indexed: 12/13/2022] Open
Abstract
Cohesin, a multisubunit protein complex, is required for holding sister chromatids together during mitosis and meiosis. The recruitment of cohesin by the sister chromatid cohesion 2/4 (SCC2/4) complex has been extensively studied in Saccharomyces cerevisiae mitosis, but its role in mitosis and meiosis remains poorly understood in multicellular organisms, because complete loss-of-function of either gene causes embryonic lethality. Here, we identified a weak allele of Atscc2 (Atscc2-5) that has only minor defects in vegetative development but exhibits a significant reduction in fertility. Cytological analyses of Atscc2-5 reveal multiple meiotic phenotypes including defects in chromosomal axis formation, meiosis-specific cohesin loading, homolog pairing and synapsis, and AtSPO11-1-dependent double strand break repair. Surprisingly, even though AtSCC2 interacts with AtSCC4 in vitro and in vivo, meiosis-specific knockdown of AtSCC4 expression does not cause any meiotic defect, suggesting that the SCC2-SCC4 complex has divergent roles in mitosis and meiosis. SCC2 homologs from land plants have a unique plant homeodomain (PHD) motif not found in other species. We show that the AtSCC2 PHD domain can bind to the N terminus of histones and is required for meiosis but not mitosis. Taken together, our results provide evidence that unlike SCC2 in other organisms, SCC2 requires a functional PHD domain during meiosis in land plants.
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Affiliation(s)
- Hongkuan Wang
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
- Center for Epigenetics, Van Andel Institute, Grand Rapids, Michigan, United States of America
| | - Wanyue Xu
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Yujin Sun
- Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Qichao Lian
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Cong Wang
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Chaoyi Yu
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Chengpeng He
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Jun Wang
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Hong Ma
- Department of Biology, the Huck Institutes of the Life Sciences, the Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Gregory P. Copenhaver
- Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Yingxiang Wang
- State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
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14
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Maximising recombination across macadamia populations to generate linkage maps for genome anchoring. Sci Rep 2020; 10:5048. [PMID: 32193408 PMCID: PMC7081209 DOI: 10.1038/s41598-020-61708-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 02/24/2020] [Indexed: 01/02/2023] Open
Abstract
The Proteaceae genus Macadamia has a recent history of domestication as a commercial nut crop. We aimed to establish the first sequence-based haploid-correlated reference genetic linkage maps for this primarily outcrossing perennial tree crop, with marker density suitable for genome anchoring. Four first generation populations were used to maximise the segregation patterns available within full-sib, biparental and self-pollinated progeny. This allowed us to combine segregation data from overlapping subsets of >4,000 informative sequence-tagged markers to increase the effective coverage of the karyotype represented by the recombinant crossover events detected. All maps had 14 linkage groups, corresponding to the Macadamia haploid chromosome number, and enabled the anchoring and orientation of sequence scaffolds to construct a pseudo-chromosomal genome assembly for macadamia. Comparison of individual maps indicated a high level of congruence, with minor discrepancies satisfactorily resolved within the integrated maps. The combined set of maps significantly improved marker density and the proportion (70%) of the genome sequence assembly anchored. Overall, increasing our understanding of the genetic landscape and genome for this nut crop represents a substantial advance in macadamia genetics and genomics. The set of maps, large number of sequence-based markers and the reconstructed genome provide a toolkit to underpin future breeding that should help to extend the macadamia industry as well as provide resources for the long term conservation of natural populations in eastern Australia of this unique genus.
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15
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Amundson KR, Ordoñez B, Santayana M, Tan EH, Henry IM, Mihovilovich E, Bonierbale M, Comai L. Genomic Outcomes of Haploid Induction Crosses in Potato ( Solanum tuberosum L.). Genetics 2020; 214:369-380. [PMID: 31871130 PMCID: PMC7017018 DOI: 10.1534/genetics.119.302843] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Accepted: 12/09/2019] [Indexed: 01/12/2023] Open
Abstract
The challenges of breeding autotetraploid potato (Solanum tuberosum) have motivated the development of alternative breeding strategies. A common approach is to obtain uniparental dihaploids from a tetraploid of interest through pollination with S. tuberosum Andigenum Group (formerly S. phureja) cultivars. The mechanism underlying haploid formation of these crosses is unclear, and questions regarding the frequency of paternal DNA transmission remain. Previous reports have described aneuploid and euploid progeny that, in some cases, displayed genetic markers from the haploid inducer (HI). Here, we surveyed a population of 167 presumed dihaploids for large-scale structural variation that would underlie chromosomal addition from the HI, and for small-scale introgression of genetic markers. In 19 progeny, we detected 10 of the 12 possible trisomies and, in all cases, demonstrated the noninducer parent origin of the additional chromosome. Deep sequencing indicated that occasional, short-tract signals appearing to be of HI origin were better explained as technical artifacts. Leveraging recurring copy number variation patterns, we documented subchromosomal dosage variation indicating segregation of polymorphic maternal haplotypes. Collectively, 52% of the assayed chromosomal loci were classified as dosage variable. Our findings help elucidate the genomic consequences of potato haploid induction and suggest that most potato dihaploids will be free of residual pollinator DNA.
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Affiliation(s)
- Kirk R Amundson
- Plant Biology and Genome Center, University of California, Davis, California 95616
| | - Benny Ordoñez
- Plant Biology and Genome Center, University of California, Davis, California 95616
- International Potato Center (CIP), Lima 12, Peru
| | | | - Ek Han Tan
- Plant Biology and Genome Center, University of California, Davis, California 95616
- School of Biology and Ecology, University of Maine, Orono, Maine 04469
| | - Isabelle M Henry
- Plant Biology and Genome Center, University of California, Davis, California 95616
| | | | | | - Luca Comai
- Plant Biology and Genome Center, University of California, Davis, California 95616
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16
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Goel M, Sun H, Jiao WB, Schneeberger K. SyRI: finding genomic rearrangements and local sequence differences from whole-genome assemblies. Genome Biol 2019; 20:277. [PMID: 31842948 PMCID: PMC6913012 DOI: 10.1186/s13059-019-1911-0] [Citation(s) in RCA: 449] [Impact Index Per Article: 74.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 12/02/2019] [Indexed: 01/27/2023] Open
Abstract
Genomic differences range from single nucleotide differences to complex structural variations. Current methods typically annotate sequence differences ranging from SNPs to large indels accurately but do not unravel the full complexity of structural rearrangements, including inversions, translocations, and duplications, where highly similar sequence changes in location, orientation, or copy number. Here, we present SyRI, a pairwise whole-genome comparison tool for chromosome-level assemblies. SyRI starts by finding rearranged regions and then searches for differences in the sequences, which are distinguished for residing in syntenic or rearranged regions. This distinction is important as rearranged regions are inherited differently compared to syntenic regions.
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Affiliation(s)
- Manish Goel
- Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany
| | - Hequan Sun
- Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany
| | - Wen-Biao Jiao
- Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany
| | - Korbinian Schneeberger
- Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany
- Faculty of Biology, LMU Munich, 82152 Planegg-Martinsried, Germany
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17
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Zambrano-Mila MS, Agathos SN, Reichardt JKV. Human genetics and genomics research in Ecuador: historical survey, current state, and future directions. Hum Genomics 2019; 13:64. [PMID: 31822297 PMCID: PMC6902328 DOI: 10.1186/s40246-019-0249-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 11/14/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In South America, the history of human genetics is extensive and its beginnings go back to the onset of the twentieth century. In Ecuador, the historical record of human genetics and genomics research is limited. In this context, our work analyzes the current status and historical panorama of these fields, based on bibliographic searches in Scopus, Google Scholar, PubMed, and Web of Science. RESULTS Our results determined that the oldest paper in human genetics coauthored by an Ecuadorian institution originates from the Central University of Ecuador in 1978. From a historical standpoint, the number of articles has increased since the 1990s. This growth has intensified and it is reflected in 137 manuscripts recorded from 2010 to 2019. Areas such as human population genetics, phylogeography, and forensic sciences are the core of genetics and genomics-associated research in Ecuador. Important advances have been made in the understanding of the bases of cancer, some genetic diseases, and congenital disorders. Fields such as pharmacogenetics and pharmacogenomics have begun to be explored during the last years. CONCLUSIONS This work paints a comprehensive picture and provides additional insights into the future panorama of human genetic and genomic research in Ecuador as an example of an emerging, resource-limited country with interesting phylogeographic characteristics and public health implications.
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Affiliation(s)
- Marlon S Zambrano-Mila
- School of Biological Sciences and Engineering, Yachay Tech University, San Miguel de Urcuquí, Ecuador.
| | - Spiros N Agathos
- School of Biological Sciences and Engineering, Yachay Tech University, San Miguel de Urcuquí, Ecuador.,Bioengineering Lab, Earth & Life Institute, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Juergen K V Reichardt
- Australian Institute of Tropical Health and Medicine (AITHM), James Cook University, Smithfield, QLD, Australia
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18
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Auxier B, Bazzicalupo A. Comment on 'Single nucleus sequencing reveals evidence of inter-nucleus recombination in arbuscular mycorrhizal fungi'. eLife 2019; 8:e47301. [PMID: 31650958 PMCID: PMC6814362 DOI: 10.7554/elife.47301] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 10/09/2019] [Indexed: 01/02/2023] Open
Abstract
Chen et al. recently reported evidence for inter-nucleus recombination in arbuscular mycorrhizal fungi (Chen et al., 2018a). Here, we report a reanalysis of their data. After filtering the data by excluding heterozygous sites in haploid nuclei, duplicated regions of the genome, and low-coverage depths base calls, we find the evidence for recombination to be very sparse.
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Affiliation(s)
- Benjamin Auxier
- Laboratory of GeneticsWageningen UniversityWageningenNetherlands
| | - Anna Bazzicalupo
- Department of Microbiology and ImmunologyMontana State UniversityBozemanUnited States
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19
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Gardiner LJ, Wingen LU, Bailey P, Joynson R, Brabbs T, Wright J, Higgins JD, Hall N, Griffiths S, Clavijo BJ, Hall A. Analysis of the recombination landscape of hexaploid bread wheat reveals genes controlling recombination and gene conversion frequency. Genome Biol 2019; 20:69. [PMID: 30982471 PMCID: PMC6463664 DOI: 10.1186/s13059-019-1675-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 03/13/2019] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND Sequence exchange between homologous chromosomes through crossing over and gene conversion is highly conserved among eukaryotes, contributing to genome stability and genetic diversity. A lack of recombination limits breeding efforts in crops; therefore, increasing recombination rates can reduce linkage drag and generate new genetic combinations. RESULTS We use computational analysis of 13 recombinant inbred mapping populations to assess crossover and gene conversion frequency in the hexaploid genome of wheat (Triticum aestivum). We observe that high-frequency crossover sites are shared between populations and that closely related parents lead to populations with more similar crossover patterns. We demonstrate that gene conversion is more prevalent and covers more of the genome in wheat than in other plants, making it a critical process in the generation of new haplotypes, particularly in centromeric regions where crossovers are rare. We identify quantitative trait loci for altered gene conversion and crossover frequency and confirm functionality for a novel RecQ helicase gene that belongs to an ancient clade that is missing in some plant lineages including Arabidopsis. CONCLUSIONS This is the first gene to be demonstrated to be involved in gene conversion in wheat. Harnessing the RecQ helicase has the potential to break linkage drag utilizing widespread gene conversions.
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Affiliation(s)
| | | | | | | | | | | | - James D. Higgins
- Department of Genetics and Genome Biology, University of Leicester, Leicester, LE1 7RH UK
| | - Neil Hall
- Earlham Institute, Norwich, NR4 7UZ UK
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ UK
| | | | | | - Anthony Hall
- Earlham Institute, Norwich, NR4 7UZ UK
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ UK
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20
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Microsatellite Borders and Micro-sequence Conservation in Juglans. Sci Rep 2019; 9:3748. [PMID: 30842460 PMCID: PMC6403238 DOI: 10.1038/s41598-019-39793-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 12/21/2018] [Indexed: 11/21/2022] Open
Abstract
Walnuts (Juglans spp.) are economically important nut and timber species with a worldwide distribution. Using the published Persian walnut genome as a reference for the assembly of short reads from six Juglans species and several interspecific hybrids, we identified simple sequence repeats in 12 Juglans nuclear and organellar genomes. The genome-wide distribution and polymorphisms of nuclear and organellar microsatellites (SSRs) for most Juglans genomes have not been previously studied. We compared the frequency of nuclear SSR motifs and their lengths across Juglans, and identified section-specific chloroplast SSR motifs. Primer pairs were designed for more than 60,000 SSR-containing sequences based on alignment against assembled scaffold sequences. Of the >60,000 loci, 39,000 were validated by e-PCR using unique primer pairs. We identified primers containing 100% sequence identity in multiple species. Across species, sequence identity in the SSR-flanking regions was generally low. Although SSRs are common and highly dispersed in the genome, their flanking sequences are conserved at about 90 to 95% identity within Juglans and within species. In a few rare cases, flanking sequences are identical across species of Juglans. This comprehensive report of nuclear and organellar SSRs in Juglans and the generation of validated SSR primers will be a useful resource for future genetic analyses, walnut breeding programs, high-level taxonomic evaluations, and genomic studies in Juglandaceae.
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21
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Liu S, Schnable JC, Ott A, Yeh CTE, Springer NM, Yu J, Muehlbauer G, Timmermans MCP, Scanlon MJ, Schnable PS. Intragenic Meiotic Crossovers Generate Novel Alleles with Transgressive Expression Levels. Mol Biol Evol 2018; 35:2762-2772. [PMID: 30184112 PMCID: PMC6231493 DOI: 10.1093/molbev/msy174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Meiotic recombination is an evolutionary force that generates new genetic diversity upon which selection can act. Whereas multiple studies have assessed genome-wide patterns of recombination and specific cases of intragenic recombination, few studies have assessed intragenic recombination genome-wide in higher eukaryotes. We identified recombination events within or near genes in a population of maize recombinant inbred lines (RILs) using RNA-sequencing data. Our results are consistent with case studies that have shown that intragenic crossovers cluster at the 5′ ends of some genes. Further, we identified cases of intragenic crossovers that generate transgressive transcript accumulation patterns, that is, recombinant alleles displayed higher or lower levels of expression than did nonrecombinant alleles in any of ∼100 RILs, implicating intragenic recombination in the generation of new variants upon which selection can act. Thousands of apparent gene conversion events were identified, allowing us to estimate the genome-wide rate of gene conversion at SNP sites (4.9 × 10−5). The density of syntenic genes (i.e., those conserved at the same genomic locations since the divergence of maize and sorghum) exhibits a substantial correlation with crossover frequency, whereas the density of nonsyntenic genes (i.e., those which have transposed or been lost subsequent to the divergence of maize and sorghum) shows little correlation, suggesting that crossovers occur at higher rates in syntenic genes than in nonsyntenic genes. Increased rates of crossovers in syntenic genes could be either a consequence of the evolutionary conservation of synteny or a biological process that helps to maintain synteny.
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Affiliation(s)
- Sanzhen Liu
- Department of Plant Pathology, Kansas State University, Manhattan, KS.,Department of Agronomy, Iowa State University, Ames, IA
| | - James C Schnable
- Department of Agriculture and Horticulture, University of Nebraska-Lincoln, Lincoln, NE
| | - Alina Ott
- Department of Agronomy, Iowa State University, Ames, IA.,Roche Sequencing Solutions, 500 S Rosa Road, Madison, WI
| | | | - Nathan M Springer
- Department of Plant and Microbial Biology, Microbial and Plant Genomics Institute, University of Minnesota, Saint Paul, MN
| | - Jianming Yu
- Department of Agronomy, Iowa State University, Ames, IA
| | - Gary Muehlbauer
- Department of Agronomy and Plant Genetics, Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, MN
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22
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de Haas LS, Koopmans R, Lelivelt CLC, Ursem R, Dirks R, Velikkakam James G. Low-coverage resequencing detects meiotic recombination pattern and features in tomato RILs. DNA Res 2018; 24:549-558. [PMID: 28605512 PMCID: PMC5726486 DOI: 10.1093/dnares/dsx024] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 05/18/2017] [Indexed: 12/14/2022] Open
Abstract
Traditional plant breeding relies on meiotic recombination for mixing of parental alleles to create novel allele combinations. Detailed analysis of recombination patterns in model organisms shows that recombination is tightly regulated within the genome, but frequencies vary extensively along chromosomes. Despite being a model organism for fruit developmental studies, high-resolution recombination patterns are lacking in tomato. In this study, we developed a novel methodology to use low-coverage resequencing to identify genome-wide recombination patterns and applied this methodology on 60 tomato Recombinant Inbred Lines (RILs). Our methodology identifies polymorphic markers from the low-coverage resequencing population data and utilizes the same data to locate the recombination breakpoints in individuals by using a variable sliding window. We identified 1,445 recombination sites comprising 112 recombination prone regions enriched for AT-rich DNA motifs. Furthermore, the recombination prone regions in tomato preferably occurred in gene promoters over intergenic regions, an observation consistent with Arabidopsis thaliana, Zea mays and Mimulus guttatus. Overall, our cost effective method and findings enhance the understanding of meiotic recombination in tomato and suggest evolutionarily conserved recombination associated genomic features.
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Affiliation(s)
- Lars S de Haas
- Rijk Zwaan Breeding B.V., 4793 RS Fijnaart, The Netherlands
| | - Roy Koopmans
- Rijk Zwaan Breeding B.V., 4793 RS Fijnaart, The Netherlands
| | | | - Remco Ursem
- Rijk Zwaan Breeding B.V., 4793 RS Fijnaart, The Netherlands
| | - Rob Dirks
- Rijk Zwaan Breeding B.V., 4793 RS Fijnaart, The Netherlands
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23
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Zhou R, Macaya-Sanz D, Rodgers-Melnick E, Carlson CH, Gouker FE, Evans LM, Schmutz J, Jenkins JW, Yan J, Tuskan GA, Smart LB, DiFazio SP. Characterization of a large sex determination region in Salix purpurea L. (Salicaceae). Mol Genet Genomics 2018; 293:1437-1452. [PMID: 30022352 DOI: 10.1007/s00438-018-1473-y] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 07/09/2018] [Indexed: 12/30/2022]
Abstract
Dioecy has evolved numerous times in plants, but heteromorphic sex chromosomes are apparently rare. Sex determination has been studied in multiple Salix and Populus (Salicaceae) species, and P. trichocarpa has an XY sex determination system on chromosome 19, while S. suchowensis and S. viminalis have a ZW system on chromosome 15. Here we use whole genome sequencing coupled with quantitative trait locus mapping and a genome-wide association study to characterize the genomic composition of the non-recombining portion of the sex determination region. We demonstrate that Salix purpurea also has a ZW system on chromosome 15. The sex determination region has reduced recombination, high structural polymorphism, an abundance of transposable elements, and contains genes that are involved in sex expression in other plants. We also show that chromosome 19 contains sex-associated markers in this S. purpurea assembly, along with other autosomes. This raises the intriguing possibility of a translocation of the sex determination region within the Salicaceae lineage, suggesting a common evolutionary origin of the Populus and Salix sex determination loci.
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Affiliation(s)
- Ran Zhou
- Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506-6057, USA
| | - David Macaya-Sanz
- Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506-6057, USA
| | - Eli Rodgers-Melnick
- Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506-6057, USA
| | - Craig H Carlson
- Horticulture Section, School of Integrative Plant Science, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, 14456, USA
| | - Fred E Gouker
- Horticulture Section, School of Integrative Plant Science, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, 14456, USA
| | - Luke M Evans
- Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506-6057, USA
| | - Jeremy Schmutz
- HudsonAlpha Institute of Biotechnology, 601 Genome Way Northwest, Huntsville, AL, 35806, USA.,Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Jerry W Jenkins
- HudsonAlpha Institute of Biotechnology, 601 Genome Way Northwest, Huntsville, AL, 35806, USA
| | - Juying Yan
- Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Gerald A Tuskan
- Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA.,Biosciences Division, Oak Ridge National Lab, Oak Ridge, USA
| | - Lawrence B Smart
- Horticulture Section, School of Integrative Plant Science, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, 14456, USA
| | - Stephen P DiFazio
- Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506-6057, USA.
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24
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Abstract
Meiosis halves diploid chromosome numbers to haploid levels that are essential for sexual reproduction in most eukaryotes. Meiotic recombination ensures the formation of bivalents between homologous chromosomes (homologs) and their subsequent proper segregation. It also results in genetic diversity among progeny that influences evolutionary responses to selection. Moreover, crop breeding depends upon the action of meiotic recombination to rearrange elite traits between parental chromosomes. An understanding of the molecular mechanisms that drive meiotic recombination is important for both fundamental research and practical applications. This review emphasizes advances made during the past 5 years, primarily in Arabidopsis and rice, by summarizing newly characterized genes and proteins and examining the regulatory mechanisms that modulate their action.
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Affiliation(s)
- Yingxiang Wang
- State Key Laboratory of Genetic Engineering and Collaborative Innovation Center of Genetics and Development, Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200438, China;
| | - Gregory P Copenhaver
- Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280, USA;
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-3280, USA
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25
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Clinical significance of germline copy number variation in susceptibility of human diseases. J Genet Genomics 2018; 45:3-12. [PMID: 29396143 DOI: 10.1016/j.jgg.2018.01.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 12/27/2017] [Accepted: 01/02/2018] [Indexed: 02/06/2023]
Abstract
Germline copy number variation (CNV) is considered to be an important form of human genetic polymorphisms. Previous studies have identified amounts of CNVs in human genome by advanced technologies, such as comparative genomic hybridization, single nucleotide genotyping, and high-throughput sequencing. CNV is speculated to be derived from multiple mechanisms, such as nonallelic homologous recombination (NAHR) and nonhomologous end-joining (NHEJ). CNVs cover a much larger genome scale than single nucleotide polymorphisms (SNPs), and may alter gene expression levels by means of gene dosage, gene fusion, gene disruption, and long-range regulation effects, thus affecting individual phenotypes and playing crucial roles in human pathogenesis. The number of studies linking CNVs with common complex diseases has increased dramatically in recent years. Here, we provide a comprehensive review of the current understanding of germline CNVs, and summarize the association of germline CNVs with the susceptibility to a wide variety of human diseases that were identified in recent years. We also propose potential issues that should be addressed in future studies.
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26
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Potter S, Bragg JG, Blom MPK, Deakin JE, Kirkpatrick M, Eldridge MDB, Moritz C. Chromosomal Speciation in the Genomics Era: Disentangling Phylogenetic Evolution of Rock-wallabies. Front Genet 2017; 8:10. [PMID: 28265284 PMCID: PMC5301020 DOI: 10.3389/fgene.2017.00010] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 01/18/2017] [Indexed: 12/24/2022] Open
Abstract
The association of chromosome rearrangements (CRs) with speciation is well established, and there is a long history of theory and evidence relating to "chromosomal speciation." Genomic sequencing has the potential to provide new insights into how reorganization of genome structure promotes divergence, and in model systems has demonstrated reduced gene flow in rearranged segments. However, there are limits to what we can understand from a small number of model systems, which each only tell us about one episode of chromosomal speciation. Progressing from patterns of association between chromosome (and genic) change, to understanding processes of speciation requires both comparative studies across diverse systems and integration of genome-scale sequence comparisons with other lines of evidence. Here, we showcase a promising example of chromosomal speciation in a non-model organism, the endemic Australian marsupial genus Petrogale. We present initial phylogenetic results from exon-capture that resolve a history of divergence associated with extensive and repeated CRs. Yet it remains challenging to disentangle gene tree heterogeneity caused by recent divergence and gene flow in this and other such recent radiations. We outline a way forward for better integration of comparative genomic sequence data with evidence from molecular cytogenetics, and analyses of shifts in the recombination landscape and potential disruption of meiotic segregation and epigenetic programming. In all likelihood, CRs impact multiple cellular processes and these effects need to be considered together, along with effects of genic divergence. Understanding the effects of CRs together with genic divergence will require development of more integrative theory and inference methods. Together, new data and analysis tools will combine to shed light on long standing questions of how chromosome and genic divergence promote speciation.
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Affiliation(s)
- Sally Potter
- Research School of Biology, Australian National University, ActonACT, Australia
- Australian Museum Research Institute, Australian Museum, SydneyNSW, Australia
| | - Jason G. Bragg
- National Herbarium of New South Wales, The Royal Botanic Gardens and Domain Trust, SydneyNSW, Australia
| | - Mozes P. K. Blom
- Department of Bioinformatics and Genetics, Swedish Museum of Natural HistoryStockholm, Sweden
| | - Janine E. Deakin
- Institute for Applied Ecology, University of Canberra, BruceACT, Australia
| | - Mark Kirkpatrick
- Department of Integrative Biology, University of Texas, AustinTX, USA
| | - Mark D. B. Eldridge
- Australian Museum Research Institute, Australian Museum, SydneyNSW, Australia
| | - Craig Moritz
- Research School of Biology, Australian National University, ActonACT, Australia
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Demirci S, van Dijk ADJ, Sanchez Perez G, Aflitos SA, de Ridder D, Peters SA. Distribution, position and genomic characteristics of crossovers in tomato recombinant inbred lines derived from an interspecific cross between Solanum lycopersicum and Solanum pimpinellifolium. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2017; 89:554-564. [PMID: 27797425 DOI: 10.1111/tpj.13406] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 10/21/2016] [Accepted: 10/21/2016] [Indexed: 05/20/2023]
Abstract
We determined the crossover (CO) distribution, frequency and genomic sequences involved in interspecies meiotic recombination by using parent-assigned variants of 52 F6 recombinant inbred lines obtained from a cross between tomato, Solanum lycopersicum, and its wild relative, Solanum pimpinellifolium. The interspecific CO frequency was 80% lower than reported for intraspecific tomato crosses. We detected regions showing a relatively high and low CO frequency, so-called hot and cold regions. Cold regions coincide to a large extent with the heterochromatin, although we found a limited number of smaller cold regions in the euchromatin. The CO frequency was higher at the distal ends of chromosomes than in pericentromeric regions and higher in short arm euchromatin. Hot regions of CO were detected in euchromatin, and COs were more often located in non-coding regions near the 5' untranslated region of genes than expected by chance. Besides overrepresented CCN repeats, we detected poly-A/T and AT-rich motifs enriched in 1-kb promoter regions flanking the CO sites. The most abundant sequence motifs at CO sites share weak similarity to transcription factor-binding sites, such as for the C2H2 zinc finger factors class and MADS box factors, while InterPro scans detected enrichment for genes possibly involved in the repair of DNA breaks.
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Affiliation(s)
- Sevgin Demirci
- Bioinformatics Group, Wageningen University and Research, Wageningen, The Netherlands
- Business Unit of Bioscience, Cluster Applied Bioinformatics, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
| | - Aalt D J van Dijk
- Business Unit of Bioscience, Cluster Applied Bioinformatics, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
- Biometris, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
| | - Gabino Sanchez Perez
- Bioinformatics Group, Wageningen University and Research, Wageningen, The Netherlands
- Business Unit of Bioscience, Cluster Applied Bioinformatics, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
| | - Saulo A Aflitos
- Business Unit of Bioscience, Cluster Applied Bioinformatics, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
| | - Dick de Ridder
- Bioinformatics Group, Wageningen University and Research, Wageningen, The Netherlands
| | - Sander A Peters
- Business Unit of Bioscience, Cluster Applied Bioinformatics, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
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28
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Ziolkowski PA, Henderson IR. Interconnections between meiotic recombination and sequence polymorphism in plant genomes. THE NEW PHYTOLOGIST 2017; 213:1022-1029. [PMID: 27861941 DOI: 10.1111/nph.14265] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Accepted: 09/02/2016] [Indexed: 06/06/2023]
Abstract
1022 I. 1022 II. 1023 III. 1023 IV. 1025 V. 1026 1027 References 1027 SUMMARY: Meiosis is fundamental to sexual reproduction and creates genetic variation in progeny. During meiosis paired homologous chromosomes undergo recombination, which can result in reciprocal crossovers. This process can recombine independently arising mutations onto the same chromosome. Recombination locations are highly variable between meioses, although total crossover numbers are tightly regulated. In addition to the effect of meiosis on genetic variation, sequence polymorphisms between homologous chromosomes can feedback onto the recombination pathways. Here we review the major crossover pathways in plants and some of the known homeostatic mechanisms that act during meiotic recombination. We then examine how sequence polymorphisms between homologous chromosomes, that is, heterozygosity, can influence meiotic recombination pathways in cis and trans. Finally, we provide a brief perspective on the relevance of these interconnections for natural selection and adaptation in plants.
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Affiliation(s)
- Piotr A Ziolkowski
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
- Department of Biotechnology, Adam Mickiewicz University, Umultowska 89, Poznan, 61-614, Poland
| | - Ian R Henderson
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
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29
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Anovazzi G, Medeiros MC, Pigossi SC, Finoti LS, Souza Moreira TM, Mayer MPA, Zanelli CF, Valentini SR, Rossa-Junior C, Scarel-Caminaga RM. Functionality and opposite roles of two interleukin 4 haplotypes in immune cells. Genes Immun 2017; 18:33-41. [PMID: 28053321 PMCID: PMC5303765 DOI: 10.1038/gene.2016.47] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 10/20/2016] [Accepted: 11/08/2016] [Indexed: 01/04/2023]
Abstract
Cytokines expression can be influenced by polymorphisms in their respective coding genes. We associated the CTI/TTD haplotype (Hap-1) and TCI/CCI haplotype (Hap-2) in the IL4 gene formed by the -590, +33 and variable number of tandem repeat polymorphisms with the severity of chronic periodontitis in humans. The functionality of these IL4 haplotypes in the response of immune cells to phorbol 12-myristate 13-acetate (PMA) with Ionomycin and IL-1β (as inflammatory stimuli) was evaluated. Gene expression (quantitative real-time PCR), profile of secreted cytokines (multiplex) and phenotypic polarization of T cells (flow cytometry) were the outcomes assessed. Green fluorescent protein reporter plasmid constructs containing specific IL4 haplotype were transiently transfected into JM cells to assess the influence of the individual haplotypes on promoter activity. In response to inflammatory stimuli the immune cells from Hap-1 haplotype had increased expression of anti-inflammatory IL4; conversely, the Hap-2 haplotype showed higher levels of pro-inflammatory cytokines. The haplotype CTI proved to be the most important for the regulation of IL4 promoter, regardless of the nature of the inflammatory stimulation; whereas the polymorphism in the promoter region had the least functional effect. In conclusion, IL4 haplotypes studied are functional and trigger opposite immune responses: anti-inflammatory (Hap-1) and pro-inflammatory (Hap-2). In addition, we identified the CTI haplotype as the main responsible for the regulation of IL4 transcriptional activity.
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Affiliation(s)
- G Anovazzi
- Department of Oral Diagnosis and Surgery, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, Araraquara, São Paulo, Brazil
| | - M C Medeiros
- Department of Oral Diagnosis and Surgery, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, Araraquara, São Paulo, Brazil
| | - S C Pigossi
- Department of Oral Diagnosis and Surgery, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, Araraquara, São Paulo, Brazil
| | - L S Finoti
- Department of Oral Diagnosis and Surgery, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, Araraquara, São Paulo, Brazil
| | - T M Souza Moreira
- Department of Biological Sciences, School of Pharmaceutical Sciences, Univ Estadual Paulista - UNESP, Araraquara, São Paulo, Brazil
| | - M P A Mayer
- Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - C F Zanelli
- Department of Biological Sciences, School of Pharmaceutical Sciences, Univ Estadual Paulista - UNESP, Araraquara, São Paulo, Brazil
| | - S R Valentini
- Department of Biological Sciences, School of Pharmaceutical Sciences, Univ Estadual Paulista - UNESP, Araraquara, São Paulo, Brazil
| | - C Rossa-Junior
- Department of Oral Diagnosis and Surgery, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, Araraquara, São Paulo, Brazil
| | - R M Scarel-Caminaga
- Department of Morphology, School of Dentistry at Araraquara, UNESP-Univ Estadual Paulista, São Paulo, Brazil
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30
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Korunes KL, Noor MAF. Gene conversion and linkage: effects on genome evolution and speciation. Mol Ecol 2016; 26:351-364. [DOI: 10.1111/mec.13736] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 06/07/2016] [Accepted: 06/22/2016] [Indexed: 12/12/2022]
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31
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Chromosome-level assembly of Arabidopsis thaliana Ler reveals the extent of translocation and inversion polymorphisms. Proc Natl Acad Sci U S A 2016; 113:E4052-60. [PMID: 27354520 DOI: 10.1073/pnas.1607532113] [Citation(s) in RCA: 144] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Resequencing or reference-based assemblies reveal large parts of the small-scale sequence variation. However, they typically fail to separate such local variation into colinear and rearranged variation, because they usually do not recover the complement of large-scale rearrangements, including transpositions and inversions. Besides the availability of hundreds of genomes of diverse Arabidopsis thaliana accessions, there is so far only one full-length assembled genome: the reference sequence. We have assembled 117 Mb of the A. thaliana Landsberg erecta (Ler) genome into five chromosome-equivalent sequences using a combination of short Illumina reads, long PacBio reads, and linkage information. Whole-genome comparison against the reference sequence revealed 564 transpositions and 47 inversions comprising ∼3.6 Mb, in addition to 4.1 Mb of nonreference sequence, mostly originating from duplications. Although rearranged regions are not different in local divergence from colinear regions, they are drastically depleted for meiotic recombination in heterozygotes. Using a 1.2-Mb inversion as an example, we show that such rearrangement-mediated reduction of meiotic recombination can lead to genetically isolated haplotypes in the worldwide population of A. thaliana Moreover, we found 105 single-copy genes, which were only present in the reference sequence or the Ler assembly, and 334 single-copy orthologs, which showed an additional copy in only one of the genomes. To our knowledge, this work gives first insights into the degree and type of variation, which will be revealed once complete assemblies will replace resequencing or other reference-dependent methods.
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32
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Melamed-Bessudo C, Shilo S, Levy AA. Meiotic recombination and genome evolution in plants. CURRENT OPINION IN PLANT BIOLOGY 2016; 30:82-7. [PMID: 26939088 DOI: 10.1016/j.pbi.2016.02.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 02/07/2016] [Accepted: 02/08/2016] [Indexed: 05/22/2023]
Abstract
Homologous recombination affects genome evolution through crossover, gene conversion and point mutations. Whole genome sequencing together with a detailed epigenome analysis have shed new light on our understanding of how meiotic recombination shapes plant genes and genome structure. Crossover events are associated with DNA sequence motifs, together with an open chromatin signature (hypomethylated CpGs, low nucleosome occupancy or specific histone modifications). The crossover landscape may differ between male and female meiocytes and between species. At the gene level, crossovers occur preferentially in promoter regions in Arabidopsis. In recent years, there is rising support suggesting that biased mismatch repair during meiotic recombination may increase GC content genome-wide and may be responsible for the GC content gradient found in many plant genes.
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Affiliation(s)
- Cathy Melamed-Bessudo
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Shay Shilo
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Avraham A Levy
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel.
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33
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Abstract
Darwin's theory of evolution by natural selection is the foundation of modern biology. However, it has proven remarkably difficult to demonstrate at the genetic, genomic, and population level exactly how wild species adapt to their natural environments. We discuss how one can use large sets of multiple genome sequences from wild populations to understand adaptation, with an emphasis on the small herbaceous plant Arabidopsis thaliana. We present motivation for such studies; summarize progress in describing whole-genome, species-wide sequence variation; and then discuss what insights have emerged from these resources, either based on sequence information alone or in combination with phenotypic data. We conclude with thoughts on opportunities with other plant species and the impact of expected progress in sequencing technology and genome engineering for studying adaptation in nature.
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Affiliation(s)
- Detlef Weigel
- Max Planck Institute for Developmental Biology, 72076 Tübingen, Germany;
| | - Magnus Nordborg
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, 1030 Vienna, Austria;
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34
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Shilo S, Melamed-Bessudo C, Dorone Y, Barkai N, Levy AA. DNA Crossover Motifs Associated with Epigenetic Modifications Delineate Open Chromatin Regions in Arabidopsis. THE PLANT CELL 2015; 27:2427-36. [PMID: 26381163 PMCID: PMC4815091 DOI: 10.1105/tpc.15.00391] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Accepted: 08/31/2015] [Indexed: 05/14/2023]
Abstract
The rate of crossover, the reciprocal exchanges of homologous chromosomal segments, is not uniform along chromosomes differing between male and female meiocytes. To better understand the factors regulating this variable landscape, we performed a detailed genetic and epigenetic analysis of 737 crossover events in Arabidopsis thaliana. Crossovers were more frequent than expected in promoters. Three DNA motifs enriched in crossover regions and less abundant in crossover-poor pericentric regions were identified. One of these motifs, the CCN repeat, was previously unknown in plants. The A-rich motif was preferentially associated with promoters, while the CCN repeat and the CTT repeat motifs were preferentially associated with genes. Analysis of epigenetic modifications around the motifs showed, in most cases, a specific epigenetic architecture. For example, we show that there is a peak of nucleosome occupancy and of H3K4me3 around the CCN and CTT repeat motifs while nucleosome occupancy was lowest around the A-rich motif. Cytosine methylation levels showed a gradual decrease within ∼2 kb of the three motifs, being lowest at sites where crossover occurred. This landscape was conserved in the decreased DNA methylation1 mutant. In summary, the crossover motifs are associated with epigenetic landscapes corresponding to open chromatin and contributing to the nonuniformity of crossovers in Arabidopsis.
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Affiliation(s)
- Shay Shilo
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Cathy Melamed-Bessudo
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yanniv Dorone
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel Département de Biologie, Ecole Normale Supérieure de Lyon, Lyon 69007, France
| | - Naama Barkai
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Avraham A Levy
- Plant and Environmental Sciences Department, The Weizmann Institute of Science, Rehovot 76100, Israel
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35
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Choi K, Henderson IR. Meiotic recombination hotspots - a comparative view. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 83:52-61. [PMID: 25925869 DOI: 10.1111/tpj.12870] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Revised: 04/15/2015] [Accepted: 04/17/2015] [Indexed: 05/18/2023]
Abstract
During meiosis homologous chromosomes pair and undergo reciprocal genetic exchange, termed crossover. Meiotic recombination has a profound effect on patterns of genetic variation and is an important tool during crop breeding. Crossovers initiate from programmed DNA double-stranded breaks that are processed to form single-stranded DNA, which can invade a homologous chromosome. Strand invasion events mature into double Holliday junctions that can be resolved as crossovers. Extensive variation in the frequency of meiotic recombination occurs along chromosomes and is typically focused in narrow hotspots, observed both at the level of DNA breaks and final crossovers. We review methodologies to profile hotspots at different steps of the meiotic recombination pathway that have been used in different eukaryote species. We then discuss what these studies have revealed concerning specification of hotspot locations and activity and the contributions of both genetic and epigenetic factors. Understanding hotspots is important for interpreting patterns of genetic variation in populations and how eukaryotic genomes evolve. In addition, manipulation of hotspots will allow us to accelerate crop breeding, where meiotic recombination distributions can be limiting.
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Affiliation(s)
- Kyuha Choi
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
| | - Ian R Henderson
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
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36
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Bayer PE, Ruperao P, Mason AS, Stiller J, Chan CKK, Hayashi S, Long Y, Meng J, Sutton T, Visendi P, Varshney RK, Batley J, Edwards D. High-resolution skim genotyping by sequencing reveals the distribution of crossovers and gene conversions in Cicer arietinum and Brassica napus. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2015; 128:1039-47. [PMID: 25754422 DOI: 10.1007/s00122-015-2488-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 02/24/2015] [Indexed: 05/03/2023]
Abstract
We characterise the distribution of crossover and non-crossover recombination in Brassica napus and Cicer arietinum using a low-coverage genotyping by sequencing pipeline SkimGBS. The growth of next-generation DNA sequencing technologies has led to a rapid increase in sequence-based genotyping for applications including diversity assessment, genome structure validation and gene-trait association. We have established a skim-based genotyping by sequencing method for crop plants and applied this approach to genotype-segregating populations of Brassica napus and Cicer arietinum. Comparison of progeny genotypes with those of the parental individuals allowed the identification of crossover and non-crossover (gene conversion) events. Our results identify the positions of recombination events with high resolution, permitting the mapping and frequency assessment of recombination in segregating populations.
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Affiliation(s)
- Philipp E Bayer
- School of Agriculture and Food Sciences, University of Queensland, Brisbane, 4072, Australia
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37
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Si W, Yuan Y, Huang J, Zhang X, Zhang Y, Zhang Y, Tian D, Wang C, Yang Y, Yang S. Widely distributed hot and cold spots in meiotic recombination as shown by the sequencing of rice F2 plants. THE NEW PHYTOLOGIST 2015; 206:1491-502. [PMID: 25664766 DOI: 10.1111/nph.13319] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 12/29/2014] [Indexed: 05/02/2023]
Abstract
Numerous studies have argued that environmental variations may contribute to evolution through the generation of novel heritable variations via meiotic recombination, which plays a crucial role in crop domestication and improvement. Rice is one of the most important staple crops, but no direct estimate of recombination events has yet been made at a fine scale. Here, we address this limitation by sequencing 41 rice individuals with high sequencing coverage and c. 900 000 accurate markers. An average of 33.9 crossover (c. 4.53 cM Mb(-1) ) and 2.47 non-crossover events were detected per F2 plant, which is similar to the values in Arabidopsis. Although not all samples in the stress treatment group showed an increased number of crossover events, environmental stress increased the recombination rate in c. 28.5% of samples. Interestingly, the crossovers showed a highly uneven distribution among and along chromosomes, with c. 13.9% of the entire genome devoid of crossovers, including 11 of the 12 centromere regions, and c. 0.72% of the genome containing large numbers of crossovers (> 50 cM Mb(-1) ). The gene ontology (GO) categories showed that genes clustered within the recombination hot spot regions primarily tended to be involved in responses to environmental stimuli, suggesting that recombination plays an important role for adaptive evolution in rapidly changing environments.
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Affiliation(s)
- Weina Si
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Yang Yuan
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Ju Huang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Xiaohui Zhang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Yanchun Zhang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Yadong Zhang
- Institute of Food Crops, Jiangsu Academy of Agricultural Science, Nanjing, 210014, China
| | - Dacheng Tian
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Cailin Wang
- Institute of Food Crops, Jiangsu Academy of Agricultural Science, Nanjing, 210014, China
| | - Yonghua Yang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
| | - Sihai Yang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, 210093, China
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38
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Ziolkowski PA, Berchowitz LE, Lambing C, Yelina NE, Zhao X, Kelly KA, Choi K, Ziolkowska L, June V, Sanchez-Moran E, Franklin C, Copenhaver GP, Henderson IR. Juxtaposition of heterozygous and homozygous regions causes reciprocal crossover remodelling via interference during Arabidopsis meiosis. eLife 2015; 4:e03708. [PMID: 25815584 PMCID: PMC4407271 DOI: 10.7554/elife.03708] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 03/26/2015] [Indexed: 12/13/2022] Open
Abstract
During meiosis homologous chromosomes undergo crossover recombination. Sequence differences between homologs can locally inhibit crossovers. Despite this, nucleotide diversity and population-scaled recombination are positively correlated in eukaryote genomes. To investigate interactions between heterozygosity and recombination we crossed Arabidopsis lines carrying fluorescent crossover reporters to 32 diverse accessions and observed hybrids with significantly higher and lower crossovers than homozygotes. Using recombinant populations derived from these crosses we observed that heterozygous regions increase crossovers when juxtaposed with homozygous regions, which reciprocally decrease. Total crossovers measured by chiasmata were unchanged when heterozygosity was varied, consistent with homeostatic control. We tested the effects of heterozygosity in mutants where the balance of interfering and non-interfering crossover repair is altered. Crossover remodeling at homozygosity-heterozygosity junctions requires interference, and non-interfering repair is inefficient in heterozygous regions. As a consequence, heterozygous regions show stronger crossover interference. Our findings reveal how varying homolog polymorphism patterns can shape meiotic recombination.
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Affiliation(s)
- Piotr A Ziolkowski
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
- Department of Biotechnology, Adam Mickiewicz University, Poznań, Poland
| | - Luke E Berchowitz
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, United States
| | - Christophe Lambing
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Nataliya E Yelina
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Xiaohui Zhao
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Krystyna A Kelly
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Kyuha Choi
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Liliana Ziolkowska
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Viviana June
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | | | - Chris Franklin
- School of Biosciences, University of Birmingham, Birmingham, United Kingdom
| | - Gregory P Copenhaver
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, United States
| | - Ian R Henderson
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
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39
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Epigenetic control of meiotic recombination in plants. SCIENCE CHINA-LIFE SCIENCES 2015; 58:223-31. [PMID: 25651968 DOI: 10.1007/s11427-015-4811-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 12/03/2014] [Indexed: 10/24/2022]
Abstract
Meiotic recombination is a deeply conserved process within eukaryotes that has a profound effect on patterns of natural genetic variation. During meiosis homologous chromosomes pair and undergo DNA double strand breaks generated by the Spo11 endonuclease. These breaks can be repaired as crossovers that result in reciprocal exchange between chromosomes. The frequency of recombination along chromosomes is highly variable, for example, crossovers are rarely observed in heterochromatin and the centromeric regions. Recent work in plants has shown that crossover hotspots occur in gene promoters and are associated with specific chromatin modifications, including H2A.Z. Meiotic chromosomes are also organized in loop-base arrays connected to an underlying chromosome axis, which likely interacts with chromatin to organize patterns of recombination. Therefore, epigenetic information exerts a major influence on patterns of meiotic recombination along chromosomes, genetic variation within populations and evolution of plant genomes.
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Rapid and inexpensive whole-genome genotyping-by-sequencing for crossover localization and fine-scale genetic mapping. G3-GENES GENOMES GENETICS 2015; 5:385-98. [PMID: 25585881 PMCID: PMC4349092 DOI: 10.1534/g3.114.016501] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The reshuffling of existing genetic variation during meiosis is important both during evolution and in breeding. The reassortment of genetic variants relies on the formation of crossovers (COs) between homologous chromosomes. The pattern of genome-wide CO distributions can be rapidly and precisely established by the short-read sequencing of individuals from F2 populations, which in turn are useful for quantitative trait locus (QTL) mapping. Although sequencing costs have decreased precipitously in recent years, the costs of library preparation for hundreds of individuals have remained high. To enable rapid and inexpensive CO detection and QTL mapping using low-coverage whole-genome sequencing of large mapping populations, we have developed a new method for library preparation along with Trained Individual GenomE Reconstruction, a probabilistic method for genotype and CO predictions for recombinant individuals. In an example case with hundreds of F2 individuals from two Arabidopsis thaliana accessions, we resolved most CO breakpoints to within 2 kb and reduced a major flowering time QTL to a 9-kb interval. In addition, an extended region of unusually low recombination revealed a 1.8-Mb inversion polymorphism on the long arm of chromosome 4. We observed no significant differences in the frequency and distribution of COs between F2 individuals with and without a functional copy of the DNA helicase gene RECQ4A. In summary, we present a new, cost-efficient method for large-scale, high-precision genotyping-by-sequencing.
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Liu H, Zhang X, Huang J, Chen JQ, Tian D, Hurst LD, Yang S. Causes and consequences of crossing-over evidenced via a high-resolution recombinational landscape of the honey bee. Genome Biol 2015; 16:15. [PMID: 25651211 PMCID: PMC4305242 DOI: 10.1186/s13059-014-0566-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 12/08/2014] [Indexed: 11/20/2022] Open
Abstract
Background Social hymenoptera, the honey bee (Apis mellifera) in particular, have ultra-high crossover rates and a large degree of intra-genomic variation in crossover rates. Aligned with haploid genomics of males, this makes them a potential model for examining the causes and consequences of crossing over. To address why social insects have such high crossing-over rates and the consequences of this, we constructed a high-resolution recombination atlas by sequencing 55 individuals from three colonies with an average marker density of 314 bp/marker. Results We find crossing over to be especially high in proximity to genes upregulated in worker brains, but see no evidence for a coupling with immune-related functioning. We detect only a low rate of non-crossover gene conversion, contrary to current evidence. This is in striking contrast to the ultrahigh crossing-over rate, almost double that previously estimated from lower resolution data. We robustly recover the predicted intragenomic correlations between crossing over and both population level diversity and GC content, which could be best explained as indirect and direct consequences of crossing over, respectively. Conclusions Our data are consistent with the view that diversification of worker behavior, but not immune function, is a driver of the high crossing-over rate in bees. While we see both high diversity and high GC content associated with high crossing-over rates, our estimate of the low non-crossover rate demonstrates that high non-crossover rates are not a necessary consequence of high recombination rates. Electronic supplementary material The online version of this article (doi:10.1186/s13059-014-0566-0) contains supplementary material, which is available to authorized users.
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Mercier R, Mézard C, Jenczewski E, Macaisne N, Grelon M. The molecular biology of meiosis in plants. ANNUAL REVIEW OF PLANT BIOLOGY 2015; 66:297-327. [PMID: 25494464 DOI: 10.1146/annurev-arplant-050213-035923] [Citation(s) in RCA: 350] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Meiosis is the cell division that reshuffles genetic information between generations. Recently, much progress has been made in understanding this process; in particular, the identification and functional analysis of more than 80 plant genes involved in meiosis have dramatically deepened our knowledge of this peculiar cell division. In this review, we provide an overview of advancements in the understanding of all aspects of plant meiosis, including recombination, chromosome synapsis, cell cycle control, chromosome distribution, and the challenge of polyploidy.
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Affiliation(s)
- Raphaël Mercier
- INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France; , , , ,
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Tennessen JA, Govindarajulu R, Ashman TL, Liston A. Evolutionary origins and dynamics of octoploid strawberry subgenomes revealed by dense targeted capture linkage maps. Genome Biol Evol 2014; 6:3295-313. [PMID: 25477420 PMCID: PMC4986458 DOI: 10.1093/gbe/evu261] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Whole-genome duplications are radical evolutionary events that have driven speciation and adaptation in many taxa. Higher-order polyploids have complex histories often including interspecific hybridization and dynamic genomic changes. This chromosomal reshuffling is poorly understood for most polyploid species, despite their evolutionary and agricultural importance, due to the challenge of distinguishing homologous sequences from each other. Here, we use dense linkage maps generated with targeted sequence capture to improve the diploid strawberry (Fragaria vesca) reference genome and to disentangle the subgenomes of the wild octoploid progenitors of cultivated strawberry, Fragaria virginiana and Fragaria chiloensis. Our novel approach, POLiMAPS (Phylogenetics Of Linkage-Map-Anchored Polyploid Subgenomes), leverages sequence reads to associate informative interhomeolog phylogenetic markers with linkage groups and reference genome positions. In contrast to a widely accepted model, we find that one of the four subgenomes originates with the diploid cytoplasm donor F. vesca, one with the diploid Fragaria iinumae, and two with an unknown ancestor close to F. iinumae. Extensive unidirectional introgression has converted F. iinumae-like subgenomes to be more F. vesca-like, but never the reverse, due either to homoploid hybridization in the F. iinumae-like diploid ancestors or else strong selection spreading F. vesca-like sequence among subgenomes through homeologous exchange. In addition, divergence between homeologous chromosomes has been substantially augmented by interchromosomal rearrangements. Our phylogenetic approach reveals novel aspects of the complicated web of genetic exchanges that occur during polyploid evolution and suggests a path forward for unraveling other agriculturally and ecologically important polyploid genomes.
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Affiliation(s)
| | | | | | - Aaron Liston
- Department of Botany and Plant Pathology, Oregon State University
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Abstract
Nucleotide diversity is greater in maize than in most organisms studied to date, so allelic pairs in a hybrid tend to be highly polymorphic. Most recombination events between such pairs of maize polymorphic alleles are crossovers. However, intragenic recombination events not associated with flanking marker exchange, corresponding to noncrossover gene conversions, predominate between alleles derived from the same progenitor. In these dimorphic heterozygotes, the two alleles differ only at the two mutant sites between which recombination is being measured. To investigate whether gene conversion at the bz locus is polarized, two large diallel crossing matrices involving mutant sites spread across the bz gene were performed and more than 2,500 intragenic recombinants were scored. In both diallels, around 90% of recombinants could be accounted for by gene conversion. Furthermore, conversion exhibited a striking polarity, with sites located within 150 bp of the start and stop codons converting more frequently than sites located in the middle of the gene. The implications of these findings are discussed with reference to recent data from genome-wide studies in other plants.
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