Decomplexifying The Bread Wheat Genome: A 1Gb Step Forward

Despite the socio-economic importance of bread wheat and the overall recognition that a reference genome sequence has great value for crop improvement, sequencing the wheat genome has long been considered “impossible” because of the sequencing cost and bioinformatic challenges associated with the assembly of the mostly repetitive 17 Gb hexaploid genome. To reduce the complexity of the analysis, the IWGSC follows a chromosome-specific approach to develop physical maps, shotgun sequencing, and high quality sequencing of the MTPs while moving towards a gold standard reference sequence. To obtain a high quality reference sequence of chromosome 3B (1Gb), we sequenced 8452 BAC clones of the MTP using Roche-454 Titanium technology and bar-coded pools of about 10 BACs each with 8 kb mate-pair libraries. A finished assembly of ~5000 scaffolds (N50= 463 kb) was obtained by combining the 454 assembly with 40’000 BAC-end sequences and Illumina PE reads (82X) of sorted 3B chromosomes. To build a 3B pseudomolecule and link the sequence to useful information for breeders, the sequenced contigs are being anchored to genetic and phenotypic maps with more than 4000 ISBP-SNP markers. Results about the annotation, structural, functional and evolutionary analyses of the 3B sequence will be presented.