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Press release.
02/10/2008
The first step towards sequencing the wheat genome: the physical map of its largest chromosome
In an unprecedented achievement, an international team led by INRA researchers from Clermont-Ferrand, Toulouse and Versailles has completed the first physical map of the largest bread wheat chromosome. Until now, the bread wheat genome has been considered impossible to physically map and sequence because of its size and complexity. This work, published in the prestigious journal SCIENCE on 3 October 2008, opens the path towards sequencing the wheat genome.
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Wheat (Triticum aestivum L.) is the staple food for 35% of the world’s population. Despite its socio-economic importance and the need for accelerated wheat genetic improvement to meet the challenges of agriculture, the tools for exploring the wheat genome are far less advanced than those developed for other cereals, such as corn, rice or sorghum. Both the size (17 billion base pairs - 5 times larger than the human genome and 40 times larger than the rice genome) and complexity (polyploid structure of 3 genomes with more than 80% of the genome composed of repetitive sequences) of the wheat genome have been stumbling blocks to traditional sequencing approaches until now.
The construction of a physical map is the first essential step towards sequencing a large genome. To reduce the complexity of mapping the entire hexaploid bread wheat genome, the INRA researchers and their colleagues have developed a strategy based on the isolation and analysis of each of the individual wheat chromosomes. They have focused first on the largest chromosome, 3B, which has nearly one billion base pairs (almost 3 times as many as the entire rice genome) to establish their proof of concept and the first physical map of a bread wheat chromosome. The 3B physical map is composed of a series of 1036 groups of DNA sequences called “contigs” that were anchored with 1443 molecular markers and ordered using a combination of different mapping approaches to reconstruct a large part of chromosome 3B. While completing this task, the researchers were faced with many difficulties inherent to the bread wheat genome, such as the lack of recombination in half of the chromosome and the reduced genetic variability found within cultivated varieties.
Physical maps constitute a precious tool for locating rapidly genes of agronomic interest and for identifying new molecular markers. They make it possible to explore regions of the genome responsible for agronomically important traits, such as yield, quality and stress resistance. As the first application of their work, the researchers located on the physical map of chromosome 3B some important genes, including a resistance gene to stem rust, a major fungal disease of wheat.
This research was conducted as a pilot project within the framework of the International Wheat Genome Sequencing Consortium (1). It shows that it is possible to construct physical maps for genomes with a chromosome-based approach regardless of the size and complexity. The work serves now as a model for other international groups to assemble the physical maps of the 20 other wheat chromosomes within the IWGSC and provides the basis for sequencing chromosome 3B in the near future. From a more general point of view, this work opens new perspectives for the analysis of genomes of other reputedly “impossible” plant species.
(1) IWGSC, www.wheatgenome.org
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References:
"A physical map of the 1Gb bread wheat chromosome 3B "
SCIENCE, 3 October 2008
Etienne Paux1, Pierre Sourdille1, Jérôme Salse1, Cyrille Saintenac1, Frédéric Choulet1,
Philippe Leroy1, Abraham Korol2, Monika Michalak3, Shahryar Kianian3, Wolfgang Spielmeyer4, Evans Lagudah4, Daryl Somers5, Andrzej Kilian6, Michael Alaux7, Sonia Vautrin8, Hélène Bergès8, Kellye Eversole9, Rudi Appels10, Jan Safar11, Hana Simkova11, Jaroslav Dolezel11, Michel Bernard1 and Catherine Feuillet1
1INRA-UBP, UMR1095, Genetics Diversity and Ecophysiology of Cereals, Clermont- Ferrand, France.
2Institute of Evolution, University of Haifa, Israel.
3Department of Plant Sciences, North Dakota State University, USA
4CSIRO Plant Industry, Canberra, Australia.
5Agriculture and Agri-Food Canada, Cereal Research Centre, Winnipeg, Canada.
6Diversity Arrays Technology Pty Ltd, Yarralumla, Australia.
7INRA-Unité de Recherches en Génomique-Info, Versailles, France.
8INRA-Centre National de Ressources Génomiques Végétales, Toulouse, France.
9International Wheat Genome Sequencing Consortium, Eversole Associates, Bethesda, USA.
10Centre for Comparative Genomics, Murdoch University, Australia.
11Laboratory of Molecular Cytogenetics and Cytometry, IEB, Olomouc, Czech Republic.
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
Sylvie Colleu, 33 (0)1 42 75 95 55 or Odile Bernard, 33 (0)4 73 62 40 35
Contacts :
Scientific contacts:
Catherine Feuillet
Tel: 33 (0)6 74 88 87 73 or 33 (0)4 73 62 46 84 or 43 03
email: catherine.feuillet@clermont.inra.fr
Etienne Paux
Tel: 33(0)4 73 62 43 86 or 43 03
email: etienne.paux@clermont.inra.fr
Joint Research Unit for Genetics, Diversity and Ecophysiology of Cereals
INRA Research Centre of Clermont-Ferrand
Plant Breeding and Genetics Division
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