Authors

Raats D, Frenkel Z, Krugman T, Dodek I, Sela H, Imková H, Magni F, Cattonaro F, Vautrin S, Bergès H, Wicker T, Keller B, Leroy P, Philippe R, Paux E, Dole El J, Feuillet C, Korol A, Fahima T

Genome Biol. 2013 Dec 20;14(12):R138.

Abstract

BACKGROUND:
The wheat genome sequence is an essential tool for advanced genomic research and improvements. The generation of a high-quality wheat genome sequence is challenging due to its complex 17 Gb polyploid genome. To overcome these difficulties, sequencing through the construction of BAC-based physical maps of individual chromosomes is employed by the wheat genomics community. Here, we present the construction of the first comprehensive physical map of chromosome 1BS, and illustrate its unique gene space organization and evolution.

RESULTS:
Fingerprinted BAC clones were assembled into 57 long scaffolds, anchored and ordered with 2,438 markers covering 83% of chromosome 1BS. The BAC-based chromosome 1BS physical map and gene order of the orthologous regions of model grass species were consistent, providing strong support for the reliability of the chromosome 1BS assembly. Chromosome 1BS gene space spans the entire length of the chromosome arm, with 76% of the genes organized in small gene-islands, accompanied by a two fold increase in gene density from the centromere to the telomere.

CONCLUSIONS:
This study provides new evidence on common and chromosome-specific features in the organization and evolution of the wheat genome, including a non-uniform distribution of gene density along the centromere-telomere axis, abundance of non-syntenic genes, the degree of colinearity with other grass genomes, and a non-uniform size expansion along the centromere-telomere axis, compared with other model cereal genomes. The high quality physical map constructed in this study provides a solid basis for the assembly of a reference sequence of chromosome 1BS and for breeding applications.

http://www.ncbi.nlm.nih.gov/pubmed/24359668

Authors

Breen J, Wicker T, Shatalina M, Frenkel Z, Bertin I, Philippe R, Spielmeyer W, Simková H, Safář J, Cattonaro F, Scalabrin S, Magni F, Vautrin S, Bergès H; International Wheat Genome Sequencing Consortium, Paux E, Fahima T, Doležel J, Korol A, Feuillet C, Keller B.

PLoS One. 8(11):e80272. doi: 10.1371/journal.pone.0080272.

Abstract

Bread wheat (Triticum aestivum) has a large and highly repetitive genome which poses major technical challenges for its study. To aid map-based cloning and future genome sequencing projects, we constructed a BAC-based physical map of the short arm of wheat chromosome 1A (1AS). From the assembly of 25,918 high information content (HICF) fingerprints from a 1AS-specific BAC library, 715 physical contigs were produced that cover almost 99% of the estimated size of the chromosome arm. The 3,414 BAC clones constituting the minimum tiling path were end-sequenced. Using a gene microarray containing ∼40 K NCBI UniGene EST clusters, PCR marker screening and BAC end sequences, we arranged 160 physical contigs (97 Mb or 35.3% of the chromosome arm) in a virtual order based on synteny with Brachypodium, rice and sorghum. BAC end sequences and information from microarray hybridisation was used to anchor 3.8 Mbp of Illumina sequences from flow-sorted chromosome 1AS to BAC contigs. Comparison of genetic and synteny-based physical maps indicated that ∼50% of all genetic recombination is confined to 14% of the physical length of the chromosome arm in the distal region. The 1AS physical map provides a framework for future genetic mapping projects as well as the basis for complete sequencing of chromosome arm 1AS.

Authors

Tayeh N, Bahrman N, Sellier H, Bluteau A, Blassiau C, Fourment J, Bellec A, Debellé F, Lejeune-Hénaut I, Delbreil B.

BMC Genomics. 2013 Nov 21;14(1):814.

Abstract

BACKGROUND:

Freezing provokes severe yield losses to different fall-sown annual legumes. Understanding the molecular bases of freezing tolerance is of great interest for breeding programs. Medicago truncatula Gaertn. is an annual temperate forage species for agronomically and economically important legume crops. The present study aimed to identify positional candidate genes for a major freezing tolerance quantitative trait locus that was previously mapped to M. truncatula chromosome 6 (Mt-FTQTL6) using the LR3 population derived from a cross between the freezing-tolerant accession F83005-5 and the freezing-sensitive accession DZA045-5.

RESULTS:

The confidence interval of Mt-FTQTL6 was narrowed down to the region comprised between markers MTIC153 and NT6054 using recombinant F7 and F8 lines. A bacterial-artificial chromosome (BAC) clone contig map was constructed in an attempt to close the residual assembly gap existing therein. Twenty positional candidate genes including twelve C-repeat binding factor (CBF)/dehydration-responsive element binding factor 1 (DREB1) genes were identified from BAC-derived sequences and whole-genome shotgun sequences (WGS). CBF/DREB1 genes are organized in a tandem array within an approximately 296-Kb region. Eleven CBF/DREB1 genes were isolated and sequenced from F83005-5 and DZA045-5 which revealed high polymorphism among these accessions. Unique features characterizing CBF/DREB1 genes from M. truncatula, such as alternative splicing and large tandem duplication, are elucidated for the first time.

CONCLUSIONS:

Overall, twenty genes were identified as potential candidates to explain Mt-FTQTL6 effect. Their future functional characterization will uncover the gene(s) involved in freezing tolerance difference observed between F83005-5 and DZA045-5. Knowledge transfer for breeding improvement of crop legumes is expected. Furthermore, CBF/DREB1 related data will certainly have a large impact on research studies targeting this group of transcriptional activators in M. truncatula and other legume species.

Authors

Ferreira de Carvalho J, Chelaifa H, Boutte J, Poulain J, Couloux A, Wincker P, Bellec A, Fourment J, Bergès H, Salmon A, Ainouche M.

Plant Mol Biol. 2013 Jul 23

Abstract

Spartina species play an important ecological role on salt marshes. Spartina maritima is an Old-World species distributed along the European and North-African Atlantic coasts. This hexaploid species (2n = 6x = 60, 2C = 3,700 Mb) hybridized with different Spartina species introduced from the American coasts, which resulted in the formation of new invasive hybrids and allopolyploids. Thus, S. maritima raises evolutionary and ecological interests. However, genomic information is dramatically lacking in this genus. In an effort to develop genomic resources, we analysed 40,641 high-quality bacterial artificial chromosome-end sequences (BESs), representing 26.7 Mb of the S. maritima genome. BESs were searched for sequence homology against known databases. A fraction of 16.91 % of the BESs represents known repeats including a majority of long terminal repeat (LTR) retrotransposons (13.67 %). Non-LTR retrotransposons represent 0.75 %, DNA transposons 0.99 %, whereas small RNA, simple repeats and low-complexity sequences account for 1.38 % of the analysed BESs. In addition, 4,285 simple sequence repeats were detected. Using the coding sequence database of Sorghum bicolor, 6,809 BESs found homology accounting for 17.1 % of all BESs. Comparative genomics with related genera reveals that the microsynteny is better conserved with S. bicolor compared to other sequenced Poaceae, where 37.6 % of the paired matching BESs are correctly orientated on the chromosomes. We did not observe large macrosyntenic rearrangements using the mapping strategy employed. However, some regions appeared to have experienced rearrangements when comparing Spartina to Sorghum and to Oryza. This work represents the first overview of S. maritima genome regarding the respective coding and repetitive components. The syntenic relationships with other grass genomes examined here help clarifying evolution in Poaceae, S. maritima being a part of the poorly-known Chloridoideae sub-family.

Link

http://www.ncbi.nlm.nih.gov/pubmed/23877482

Authors

Philippe R, Paux E, Bertin I, Sourdille P, Choulet F, Laugier C, Simkova H, Safar J, Bellec A, Vautrin S, Frenkel Z, Cattonaro F, Magni F, Scalabrin S, Martis MM, Mayer KF, Korol A, Berges H, Dolezel J, Feuillet C.

Genome Biol. 2013 Jun 25;14(6):R64. [Epub ahead of print]

Abstract

BACKGROUND:
As for other major crops, achieving a complete wheat genome sequence is essential for the application of genomics to breeding new and improved varieties. To overcome the complexities of the large, highly repetitive and hexaploid wheat genome, the International Wheat Genome Sequencing Consortium established a chromosome-based strategy that was validated by the construction of the physical map of chromosome 3B. Here, we present improved strategies for the construction of highly integrated and ordered wheat physical maps, using chromosome 1BL as a template, and illustrate their potential for evolutionary studies and map-based cloning.

RESULTS:
Using a combination of novel high throughput marker assays and an assembly program, we developed a high quality physical map representing 93% of wheat chromosome 1BL, anchored and ordered with 5,489 markers including 1,161 genes. Analysis of the gene space organization and evolution revealed that gene distribution and conservation along the chromosome results from the superimposition of the ancestral grass and recent wheat evolutionary patterns leading to a peak of synteny in the central part of the chromosome arm and an increased density of non collinear genes towards the telomere. With a density of about 11 markers per Mb, the 1BL physical map provides 916 markers, including 193 genes, for fine mapping the 40 QTLs mapped on this chromosome.

CONCLUSIONS:
Here, we demonstrate that high marker density physical maps can be developed in complex genomes such as wheat to accelerate map-based cloning, gain new insights into genome evolution, and provide a foundation for reference sequencing.:

Link : http://www.ncbi.nlm.nih.gov/pubmed/23800011

Authors

Ben C, Debellé F, Berges H, Bellec A, Jardinaud MF, Anson P, Huguet T, Gentzbittel L, Vailleau F.

New Phytol. 2013 May 2. doi: 10.1111/nph.12299.

Abstract

Ralstonia solanacearum is a major soilborne pathogen that attacks > 200 plant species, including major crops. To characterize MtQRRS1, a major quantitative trait locus (QTL) for resistance towards this bacterium in the model legume Medicago truncatula, genetic and functional approaches were combined. QTL analyses together with disease scoring of heterogeneous inbred families were used to define the locus. The candidate region was studied by physical mapping using a bacterial artificial chromosome (BAC) library of the resistant line, and sequencing. In planta bacterial growth measurements, grafting experiments and gene expression analysis were performed to investigate the mechanisms by which this locus confers resistance to R. solanacearum. The MtQRRS1 locus was localized to the same position in two recombinant inbred line populations and was narrowed down to a 64 kb region. Comparison of parental line sequences revealed 15 candidate genes with sequence polymorphisms, but no evidence of differential gene expression upon infection. A role for the hypocotyl in resistance establishment was shown. These data indicate that the quantitative resistance to bacterial wilt conferred by MtQRRS1, which contains a cluster of seven R genes, is shared by different accessions and may act through intralocus interactions to promote resistance.

Authors

Lucas SJ, Akpınar BA, Kantar M, Weinstein Z, Aydınoğlu F, Safář J, Simková H, Frenkel Z, Korol A, Magni F, Cattonaro F, Vautrin S, Bellec A, Bergès H, Doležel J, Budak H.

PLoS One. 2013 Apr 16;8(4):e59542. doi: 10.1371/journal.pone.0059542.

Abstract

BACKGROUND:

Bread wheat (Triticum aestivum L.) is one of the most important crops worldwide and its production faces pressing challenges, the solution of which demands genome information. However, the large, highly repetitive hexaploid wheat genome has been considered intractable to standard sequencing approaches. Therefore the International Wheat Genome Sequencing Consortium (IWGSC) proposes to map and sequence the genome on a chromosome-by-chromosome basis.

METHODOLOGY PRINCIPAL FINDINGS:

We have constructed a physical map of the long arm of bread wheat chromosome 1A using chromosome-specific BAC libraries by High Information Content Fingerprinting (HICF). Two alternative methods (FPC and LTC) were used to assemble the fingerprints into a high-resolution physical map of the chromosome arm. A total of 365 molecular markers were added to the map, in addition to 1122 putative unique transcripts that were identified by microarray hybridization. The final map consists of 1180 FPC-based or 583 LTC-based contigs.

CONCLUSIONS SIGNIFICANCE:

The physical map presented here marks an important step forward in mapping of hexaploid bread wheat. The map is orders of magnitude more detailed than previously available maps of this chromosome, and the assignment of over a thousand putative expressed gene sequences to specific map locations will greatly assist future functional studies. This map will be an essential tool for future sequencing of and positional cloning within chromosome 1A.