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Kajla A, Schoen A, Paulson C, Yadav IS, Neelam K, Riera-Lizarazu O, Leonard J, Gill BS, Venglat P, Datla R, Poland J, Coleman G, Rawat N, Tiwari V. Physical mapping of the wheat genes in low-recombination regions: radiation hybrid mapping of the C-locus. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2023; 136:159. [PMID: 37344686 DOI: 10.1007/s00122-023-04403-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Accepted: 06/09/2023] [Indexed: 06/23/2023]
Abstract
KEY MESSAGE This work reports the physical mapping of an important gene affecting spike compactness located in a low-recombination region of hexaploid wheat. This work paves the way for the eventual isolation and characterization of the factor involved but also opens up possibilities to use this approach to precisely map other wheat genes located on proximal parts of wheat chromosomes that show highly reduced recombination. Mapping wheat genes, in the centromeric and pericentromeric regions (~ 2/3rd of a given chromosome), poses a formidable challenge due to highly suppressed recombination. Using an example of compact spike locus (C-locus), this study provides an approach to precisely map wheat genes in the pericentromeric and centromeric regions that house ~ 30% of wheat genes. In club-wheat, spike compactness is controlled by the dominant C-locus, but previous efforts have failed to localize it, on a particular arm of chromosome 2D. We integrated radiation hybrid (RH) and high-resolution genetic mapping to locate C-locus on the short arm of chromosome 2D. Flanking markers of the C-locus span a physical distance of 11.0 Mb (231.0-242 Mb interval) and contain only 11 high-confidence annotated genes. This work demonstrates the value of this integrated strategy in mapping dominant genes in the low-recombination regions of the wheat genome. A comparison of the mapping resolutions of the RH and genetic maps using common anchored markers indicated that the RH map provides ~ 9 times better resolution that the genetic map even with much smaller population size. This study provides a broadly applicable approach to fine map wheat genes in regions of suppressed recombination.
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Affiliation(s)
- Anmol Kajla
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | - Adam Schoen
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | - Carl Paulson
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | - Inderjit Singh Yadav
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | | | | | - Jeff Leonard
- Department of Crop and Soil Sciences, Oregon State University, Corvallis, OR, USA
| | - Bikram S Gill
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA
| | | | - Raju Datla
- Global Institute of Food Security, Saskatoon, SK, Canada
| | - Jesse Poland
- Center for Desert Agriculture, KAUST, Thuwal, Saudi Arabia
| | - Gary Coleman
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | - Nidhi Rawat
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA
| | - Vijay Tiwari
- Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, College Park, USA.
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Darrier B, Colas I, Rimbert H, Choulet F, Bazile J, Sortais A, Jenczewski E, Sourdille P. Location and Identification on Chromosome 3B of Bread Wheat of Genes Affecting Chiasma Number. PLANTS (BASEL, SWITZERLAND) 2022; 11:2281. [PMID: 36079661 PMCID: PMC9460588 DOI: 10.3390/plants11172281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 08/05/2022] [Accepted: 08/08/2022] [Indexed: 11/16/2022]
Abstract
Understanding meiotic crossover (CO) variation in crops like bread wheat (Triticum aestivum L.) is necessary as COs are essential to create new, original and powerful combinations of genes for traits of agronomical interest. We cytogenetically characterized a set of wheat aneuploid lines missing part or all of chromosome 3B to identify the most influential regions for chiasma formation located on this chromosome. We showed that deletion of the short arm did not change the total number of chiasmata genome-wide, whereas this latter was reduced by ~35% while deleting the long arm. Contrary to what was hypothesized in a previous study, deletion of the long arm does not disturb the initiation of the synaptonemal complex (SC) in early meiotic stages. However, progression of the SC is abnormal, and we never observed its completion when the long arm is deleted. By studying six different deletion lines (missing different parts of the long arm), we revealed that at least two genes located in both the proximal (C-3BL2-0.22) and distal (3BL7-0.63-1.00) deletion bins are involved in the control of chiasmata, each deletion reducing the number of chiasmata by ~15%. We combined sequence analyses of deletion bins with RNA-Seq data derived from meiotic tissues and identified a set of genes for which at least the homoeologous copy on chromosome 3B is expressed and which are involved in DNA processing. Among these genes, eight (CAP-E1/E2, DUO1, MLH1, MPK4, MUS81, RTEL1, SYN4, ZIP4) are known to be involved in the recombination pathway.
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Affiliation(s)
- Benoit Darrier
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
- Syngenta, Toulouse Innovation Centre 12 Chemin de l’Hobit, 31790 Saint-Sauveur, France
| | - Isabelle Colas
- Cell and Molecular Sciences, The James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK
| | - Hélène Rimbert
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
| | - Frédéric Choulet
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
| | - Jeanne Bazile
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
| | - Aurélien Sortais
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
| | - Eric Jenczewski
- Institut Jean-Pierre Bourgin, INRAE, AgroParisTech, CNRS, Université Paris-Saclay, 78000 Versailles, France
| | - Pierre Sourdille
- UMR 1095 Genetics, Diversity and Ecophysiology of Cereals, 5, INRAE–Université Clermont-Auvergne, Chemin de Beaulieu, 63000 Clermont-Ferrand, France
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Mahlandt A, Rawat N, Leonard J, Venglat P, Datla R, Meier N, Gill BS, Riera-Lizarazu O, Coleman G, Murphy AS, Tiwari VK. High-resolution mapping of the Mov-1 locus in wheat by combining radiation hybrid (RH) and recombination-based mapping approaches. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2021; 134:2303-2314. [PMID: 33830295 DOI: 10.1007/s00122-021-03827-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 03/29/2021] [Indexed: 06/12/2023]
Abstract
This work reports a quick method that integrates RH mapping and genetic mapping to map the dominant Mov-1 locus to a 1.1-Mb physical interval with a small number of candidate genes. Bread wheat is an important crop for global human population. Identification of genes and alleles controlling agronomic traits is essential toward sustainably increasing crop production. The unique multi-ovary (MOV) trait in wheat holds potential for improving yields and is characterized by the formation of 2-3 grains per spikelet. The genetic basis of the multi-ovary trait is known to be monogenic and dominant in nature. Its precise mapping and functional characterization is critical to utilizing this trait in a feasible manner. Previous mapping efforts of the locus controlling multiple ovary/pistil formation in the hexaploid wheat have failed to produce a consensus for a particular chromosome. We describe a mapping strategy integrating radiation hybrid mapping and high-resolution genetic mapping to locate the chromosomal position of the Mov-1 locus in hexaploid wheat. We used RH mapping approach using a panel of 188 lines to map the Mov-1 locus in the terminal part of long arm of wheat chromosome 2D with a map resolution of 1.67 Mb/cR1500. Then using a genetic population of MOV × Synthetic wheat of F2 lines, we delineated the Mov-1 locus to a 1.1-Mb physical region with a small number of candidate genes. This demonstrates the value of this integrated strategy to mapping dominant genes in wheat.
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Affiliation(s)
- Alexander Mahlandt
- Department of Plant Science and Landscape Architecture, University of Maryland, College Park, USA
| | - Nidhi Rawat
- Department of Plant Science and Landscape Architecture, University of Maryland, College Park, USA
| | - Jeff Leonard
- Department of Crop and Soil Sciences, Oregon State University, Corvallis, OR, USA
| | - Prakash Venglat
- Global Institute for Food Security, University of Saskatchewan, Saskatoon, Canada
| | - Raju Datla
- Global Institute for Food Security, University of Saskatchewan, Saskatoon, Canada
| | - Nathan Meier
- Department of Plant Biology, University of California, Davis, CA, USA
| | - Bikram S Gill
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA
| | | | - Gary Coleman
- Department of Plant Science and Landscape Architecture, University of Maryland, College Park, USA
| | - Angus S Murphy
- Department of Plant Science and Landscape Architecture, University of Maryland, College Park, USA
| | - Vijay K Tiwari
- Department of Plant Science and Landscape Architecture, University of Maryland, College Park, USA.
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Buerstmayr M, Steiner B, Wagner C, Schwarz P, Brugger K, Barabaschi D, Volante A, Valè G, Cattivelli L, Buerstmayr H. High-resolution mapping of the pericentromeric region on wheat chromosome arm 5AS harbouring the Fusarium head blight resistance QTL Qfhs.ifa-5A. PLANT BIOTECHNOLOGY JOURNAL 2018; 16:1046-1056. [PMID: 29024288 PMCID: PMC5902775 DOI: 10.1111/pbi.12850] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 09/17/2017] [Accepted: 10/08/2017] [Indexed: 05/24/2023]
Abstract
The Qfhs.ifa-5A allele, contributing to enhanced Fusarium head blight resistance in wheat, resides in a low-recombinogenic region of chromosome 5A close to the centromere. A near-isogenic RIL population segregating for the Qfhs.ifa-5A resistance allele was developed and among 3650 lines as few as four recombined within the pericentromeric C-5AS1-0.40 bin, yielding only a single recombination point. Genetic mapping of the pericentromeric region using a recombination-dependent approach was thus not successful. To facilitate fine-mapping the physically large Qfhs.ifa-5A interval, two gamma-irradiated deletion panels were generated: (i) seeds of line NIL3 carrying the Qfhs.ifa-5A resistance allele in an otherwise susceptible background were irradiated and plants thereof were selfed to obtain deletions in homozygous state and (ii) a radiation hybrid panel was produced using irradiated pollen of the wheat line Chinese Spring (CS) for pollinating the CS-nullisomic5Atetrasomic5B. In total, 5157 radiation selfing and 276 radiation hybrid plants were screened for deletions on 5AS and plants containing deletions were analysed using 102 5AS-specific markers. Combining genotypic information of both panels yielded an 817-fold map improvement (cR/cM) for the centromeric bin and was 389-fold increased across the Qfhs.ifa-5A interval compared to the genetic map, with an average map resolution of 0.77 Mb/cR. We successfully proved that the RH mapping technique can effectively resolve marker order in low-recombining regions, including pericentromeric intervals, and simultaneously allow developing an in vivo panel of sister lines differing for induced deletions across the Qfhs.ifa-5A interval that can be used for phenotyping.
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Affiliation(s)
- Maria Buerstmayr
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
| | - Barbara Steiner
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
| | - Christian Wagner
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
| | - Petra Schwarz
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
| | - Klaus Brugger
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
| | - Delfina Barabaschi
- Council for Agricultural Research and Economics (CREA)Genomics Research CentreFiorenzuola d'ArdaItaly
| | - Andrea Volante
- Council for Agricultural Research and Economics (CREA)Research Centre for Cereal and Industrial CropsVercelliItaly
| | - Giampiero Valè
- Council for Agricultural Research and Economics (CREA)Research Centre for Cereal and Industrial CropsVercelliItaly
| | - Luigi Cattivelli
- Council for Agricultural Research and Economics (CREA)Genomics Research CentreFiorenzuola d'ArdaItaly
| | - Hermann Buerstmayr
- Department of Agrobiotechnology TullnBOKU ‐ University of Natural Resources and Life Sciences, ViennaTullnAustria
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Balcárková B, Frenkel Z, Škopová M, Abrouk M, Kumar A, Chao S, Kianian SF, Akhunov E, Korol AB, Doležel J, Valárik M. A High Resolution Radiation Hybrid Map of Wheat Chromosome 4A. FRONTIERS IN PLANT SCIENCE 2017; 7:2063. [PMID: 28119729 PMCID: PMC5222868 DOI: 10.3389/fpls.2016.02063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 12/26/2016] [Indexed: 05/18/2023]
Abstract
Bread wheat has a large and complex allohexaploid genome with low recombination level at chromosome centromeric and peri-centromeric regions. This significantly hampers ordering of markers, contigs of physical maps and sequence scaffolds and impedes obtaining of high-quality reference genome sequence. Here we report on the construction of high-density and high-resolution radiation hybrid (RH) map of chromosome 4A supported by high-density chromosome deletion map. A total of 119 endosperm-based RH lines of two RH panels and 15 chromosome deletion bin lines were genotyped with 90K iSelect single nucleotide polymorphism (SNP) array. A total of 2316 and 2695 markers were successfully mapped to the 4A RH and deletion maps, respectively. The chromosome deletion map was ordered in 19 bins and allowed precise identification of centromeric region and verification of the RH panel reliability. The 4A-specific RH map comprises 1080 mapping bins and spans 6550.9 cR with a resolution of 0.13 Mb/cR. Significantly higher mapping resolution in the centromeric region was observed as compared to recombination maps. Relatively even distribution of deletion frequency along the chromosome in the RH panel was observed and putative functional centromere was delimited within a region characterized by two SNP markers.
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Affiliation(s)
- Barbora Balcárková
- Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural ResearchOlomouc, Czechia
| | - Zeev Frenkel
- Institute of Evolution, University of HaifaHaifa, Israel
| | - Monika Škopová
- Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural ResearchOlomouc, Czechia
| | - Michael Abrouk
- Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural ResearchOlomouc, Czechia
| | - Ajay Kumar
- Department of Plant Sciences, North Dakota State University, FargoND, USA
| | - Shiaoman Chao
- Biosciences Research Laboratory, United States Department of Agriculture-Agricultural Research Service, FargoND, USA
| | - Shahryar F. Kianian
- Cereal Disease Laboratory, United States Department of Agriculture-Agricultural Research Service, University of Minnesota, St. PaulMN, USA
| | - Eduard Akhunov
- Department of Plant Pathology, Kansas State University, ManhattanKS, USA
| | | | - Jaroslav Doležel
- Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural ResearchOlomouc, Czechia
| | - Miroslav Valárik
- Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural ResearchOlomouc, Czechia
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6
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Bassi FM, Ghavami F, Hayden MJ, Wang Y, Forrest KL, Kong S, Dizon R, Michalak de Jimenez MK, Meinhardt SW, Mergoum M, Gu YQ, Kianian SF. Fast-forward genetics by radiation hybrids to saturate the locus regulating nuclear-cytoplasmic compatibility in Triticum. PLANT BIOTECHNOLOGY JOURNAL 2016; 14:1716-1726. [PMID: 26915753 PMCID: PMC5067624 DOI: 10.1111/pbi.12532] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 11/24/2015] [Accepted: 12/24/2015] [Indexed: 05/29/2023]
Abstract
The nuclear-encoded species cytoplasm specific (scs) genes control nuclear-cytoplasmic compatibility in wheat (genus Triticum). Alloplasmic cells, which have nucleus and cytoplasm derived from different species, produce vigorous and vital organisms only when the correct version of scs is present in their nucleus. In this study, bulks of in vivo radiation hybrids segregating for the scs phenotype have been genotyped by sequencing with over 1.9 million markers. The high marker saturation obtained for a critical region of chromosome 1D allowed identification of 3318 reads that mapped in close proximity of the scs. A novel in silico approach was deployed to extend these short reads to sequences of up to 70 Kb in length and identify candidate open reading frames (ORFs). Markers were developed to anchor the short contigs containing ORFs to a radiation hybrid map of 650 individuals with resolution of 288 Kb. The region containing the scs locus was narrowed to a single Bacterial Artificial Chromosome (BAC) contig of Aegilops tauschii. Its sequencing and assembly by nano-mapping allowed rapid identification of a rhomboid gene as the only ORF existing within the refined scs locus. Resequencing of this gene from multiple germplasm sources identified a single nucleotide mutation, which gives rise to a functional amino acid change. Gene expression characterization revealed that an active copy of this rhomboid exists on all homoeologous chromosomes of wheat, and depending on the specific cytoplasm each copy is preferentially expressed. Therefore, a new methodology was applied to unique genetic stocks to rapidly identify a strong candidate gene for the control of nuclear-cytoplasmic compatibility in wheat.
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Affiliation(s)
- Filippo M Bassi
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
- International Center for the Agricultural Research in the Dry Areas (ICARDA), Rabat, Morocco
| | - Farhad Ghavami
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
- Eurofins BioDiagnostics, Inc., River Falls, WI, USA
| | - Matthew J Hayden
- Department of Environment and Primary Industries, AgriBiosciences Center, Bundoora, Vic, Australia
| | - Yi Wang
- USDA-ARS, Western Regional Research Center, Albany, CA, USA
| | - Kerrie L Forrest
- Department of Environment and Primary Industries, AgriBiosciences Center, Bundoora, Vic, Australia
| | - Stephan Kong
- Department of Environment and Primary Industries, AgriBiosciences Center, Bundoora, Vic, Australia
| | - Rhoderissa Dizon
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
| | | | - Steven W Meinhardt
- Department of Plant Pathology, North Dakota State University, Fargo, ND, USA
| | - Mohamed Mergoum
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
| | - Yong Q Gu
- USDA-ARS, Western Regional Research Center, Albany, CA, USA
| | - Shahryar F Kianian
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
- USDA-ARS Cereal Disease Laboratory, University of Minnesota, Saint Paul, MN, USA
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7
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Kianian PMA, Liberatore KL, Miller ME, Hegstad JB, Kianian SF. Dissecting Plant Chromosomes by the Use of Ionizing Radiation. Methods Mol Biol 2016; 1429:91-101. [PMID: 27511169 DOI: 10.1007/978-1-4939-3622-9_8] [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] [Indexed: 06/06/2023]
Abstract
Radiation treatment of genomes is used to generate chromosome breaks for numerous applications. This protocol describes the preparation of seeds and the determination of the optimal level of irradiation dosage for the creation of a radiation hybrid (RH) population. These RH lines can be used to generate high-resolution physical maps for the assembly of sequenced genomes as well as the fine mapping of genes. This procedure can also be used for mutation breeding and forward/reverse genetics.
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Affiliation(s)
- Penny M A Kianian
- Department of Horticultural Science, University of Minnesota, 1970 Folwell Ave., St. Paul, MN, 55108, USA.
| | - Katie L Liberatore
- USDA-ARS, Cereal Disease Laboratory, Department of Plant Pathology, University of Minnesota, 1551 Lindig Ave., St. Paul, MN, 55108, USA
| | - Marisa E Miller
- Department of Horticultural Science, University of Minnesota, 1970 Folwell Ave., St. Paul, MN, 55108, USA
| | - Justin B Hegstad
- Department of Plant Sciences, North Dakota State University, Fargo, ND, USA
| | - Shahryar F Kianian
- USDA-ARS, Cereal Disease Laboratory, Department of Plant Pathology, University of Minnesota, 1551 Lindig Ave., St. Paul, MN, 55108, USA.
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Naranjo T. Forcing the shift of the crossover site to proximal regions in wheat chromosomes. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2015; 128:1855-63. [PMID: 26066968 DOI: 10.1007/s00122-015-2552-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Accepted: 05/30/2015] [Indexed: 05/23/2023]
Abstract
Terminal deletions obligate the first crossover to be formed in more proximal positions. This increases the recombination rate in intercalary intervals but not in the proximity of the centromere. Crossovers are not uniformly distributed along chromosomes in wheat. They take place preferentially in distal positions. The effect of the chromosomal architecture on crossover positioning has been analyzed from the chiasmate bonds at metaphase I formed by the truncated arms of 51 terminal deletion lines of eight wheat chromosomes. Chromosome 4A and the B genome chromosomes, in their standard or truncated conformation, and their arms, were identified by C-banding. Chromosomes studied show a similar chiasma distribution. Reduction of the size of the truncated arms is accompanied by a gradual decrease of the chiasma frequency in chromosome arms 1BL, 3BS, 3BL, 4BL, 5BS, 5BL, 6BL, 7BS, 7BL and 4AL. In chromosome arm 1BS, most chiasmata are concentrated in the distal half of the satellite and, in 4AS, in the distal 24 %. The arms 2BS, 2BL and 6BS do not show a simple decreasing gradient of the recombination rate, the chiasma frequency increases in subdistal intervals compared to more distal regions. Although terminal deletions usually induce an increase of chiasma frequency in intercalary regions, the level of intact chromosome arms is maintained in only a few deletion lines. Truncated arms containing only the 20 % proximal of the intact arm do not form chiasmata. The relationships of chiasma positioning with chromatin structure and genome organization is discussed.
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Affiliation(s)
- Tomás Naranjo
- Departamento de Genética, Facultad de Biología, Universidad Complutense, 28040, Madrid, Spain,
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