The Barley Genome

Barley is one of the most important cereal crop species. It is a close relative to wheat and rye. Its haploid genome size exceeds 5 Gigabases (Gbp), almost twice the size of any fully sequenced organism or crop species. The International Barley Sequencing Consortium (IBSC) started in 2006 a project to establish a map-based high quality reference sequence of barley. After reaching important intermediate results like (i) virtual gene order maps based on sorted chromosome survey sequencing, (ii) a whole genome shotgun draft sequence integrated to a genome-wide physical map and (iii) a draft sequence of the barley genome gene space based on pooled BAC sequencing, IBSC has come close to reach its 10 year milestone of a genome-wide BAC-by-BAC based genome sequence of barley. All seven barley chromosomes were sequenced based on short-reads sequencing-by-synthesis technology along their respective minimum tiling path of the physical map. Sequence data of more than 85,000 BAC clones was assembled and integrated with high density genetic marker information and 3D conformation capture sequencing data (HiC). As a result 4.6 Gbp of the 4.8 Gbp non-redundant sequences could be linearly ordered into seven pseudomolecules representing a first version (v1.0) reference sequence of the barley genome. A nano-channel electrophoresis based optical map of fluorescently labeled high molecular weight DNA was used to independently validate the physical integrity of the scaffolds of the pseudomolecules.