Status of the Map-Based Sequencing of the Barley Genome

Barley is a major target for genome sequencing and analysis, especially in the context of establishing genomics-based crop improvement (IBSC, http://barleygenome.org). Although the barley gene-space was described recently, advancing to the complete genome sequence remains still challenging:  The fraction of repetitive DNA is ~80%, and each of the seven chromosomes equals on average about six complete A. thaliana genomes. Hence, for sequencing the individual barley chromosomes a clone-by-clone strategy was applied, which was based on a pre-existing Minimum Tiling Path (MTP) of overlapping BAC clones established for each chromosome (~8000 – 9500 BACs/chromosome). So far, shotgun sequencing of chromosomes 1H, 2H, 3H, 4H and  5H was completed  for the most part in 2013 (IBSC). Work on the remaining chromosomes (6H, 7H) is still in progress and will be finished in 2014. Here, the sequencing approach applied to chromosomes 1H, 3H and 4H will be presented in greater detail. Using shotgun sequencing in combination with custom-tailored multiplexing (up to 670 samples) about 30000 BACs were sequenced (Illumina HiSeq2000, MiSeq and Roche 454 XL+) and assembled. Furthermore, in order to scaffold sequence contigs, 8 kb mate-pair libraries (Nextera) from pooled MTP-BAC clones were employed. In the near future the assembled map-based sequence of the barley genome will represent a valuable resource for genetics and breeding.