A Complete Set of Chromosome BAC Libraries for Genomics of Wheat (Triticum aestivum)

Bread wheat is one of the most important crops for global food security and new cultivars are needed to counter the negative effects of climate change and new pathogens impacting yield and quality. Effective applications of biotechnology and genomics to develop cultivars require a better knowledge of wheat genome. Gene mapping, cloning, and production of a reference genome sequence is hampered by its huge size (17Gbp) and polyploidy, but these tasks can be simplified by dissecting the genome into single chromosomes. We used flow cytometry to sort chromosomes 1D, 4D, and 6D as a group, chromosome 3B, and chromosome arms of the remaining seventeen chromosomes from cv. Chinese Spring. Telosomic lines were used for sorting the arms except that chromosome arm 5BL was sorted as an isochromosome. A total of 45 BAC libraries was constructed with cumulative coverage ranging from 11.8x to 26.8x for individual chromosomes / arms. The protocol was improved during the course of the project and a majority of libraries have >120kb average insert size (http://olomouc.ueb.cas.cz/dna-libraries/cereals). Due to the chromosome specificity, high coverage, large insert size and low number of clones (typically 55,000), the libraries have facilitated wheat genomics significantly. Their availability enables international collaboration on sequence-ready physical maps of wheat the minimum tiling paths of which are being used to develop the reference sequence of wheat.  Recent results have proven that coupling the chromosome-specific BAC libraries with next generation sequencing technologies provides an efficient strategy to produce the reference sequence of the complex bread wheat genome.