A Reference Wheat Genome Sequence for Accelerating Wheat Improvement for Climate Change

Bread wheat (Triticum aestivum L.), the staple food for 35% of the world’s population and the most widely produced crop, is one of the most important crop species for food and feed. Despite its socio-economic importance 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. In the past 5 years, however, new capabilities and technologies have emerged that enabled the launching of an international effort to tackle the bread wheat genome sequence. In 2005, a group of growers, breeders, and plant scientists launched the International Wheat Genome Sequencing Consortium (IWGSC) with the goal of securing a high quality, reference sequence of the bread wheat genome. A milestone-based strategy coupled with short and long-term roadmaps was established to provide breeders access to an increasing array of tools and resources without having to wait for the completed sequence. To reduce the complexity of the hexaploid (2n=6x=42, AABBDD), highly repetitive (>80%), 17Gb bread wheat genome, the IWGSC follows a chromosome-specific approach to develop physical maps, shotgun sequencing, and high quality sequencing of the Minimum Tiling Paths while moving towards a gold standard reference sequence.  To date, physical maps have been completed or are underway for all 21 chromosomes of the reference cultivar, Chinese Spring. To facilitate anchoring, marker development, and to gain a first insight into the gene space composition and evolution, the IWGSC launched an internationally coordinated survey sequencing initiative that provides breeders with shotgun sequence assemblies and a virtual order for the genes on each of the 21 chromosomes of Chinese Spring.  Wheat genome sequence resources generated by the IWGSC are being used to accelerate gene discovery and breeding for traits related to climate change.  An overview of recently developed resources and their utilization for wheat improvement will be presented.