A Next Generation Breeding Platform for Wheat – A Genome-Sequence Launching Pad

Kellye Eversole, Executive Director, IWGSC

Wheat (Triticum aestivum) is inextricably linked with the history of mankind from its discovery and domestication that enabled the rise of civilization to its current status as the most widely cultivated crop in the world and providing 44 percent of the world cereal consumption for food (www.fao.org). As the staple food for 35 percent of the world’s population, wheat provides more calories and protein in the world’s diet than any other crop. Climatic changes resulting in more dramatic episodes of drought or rain, high oil prices, increased utilization of grain for biofuels, changing diets, and expanding populations have led to rising demand for wheat. Utilization has exceeded production six out of the past eight years and, last year, wheat stocks reached their lowest level in almost 30 years. Even with increases in acreage planted worldwide, production simply has not been able to keep pace with demand. The need for the next green revolution has never been greater if we are to ensure wheat production in sufficient amount and quality in an environmental friendly manner. The key to that next revolution is the wheat genome. Hidden within the wheat genome is the clue as to why wheat can grow on more land than any other crop in the world, in a greater diversity of climates, and the key to the development of varieties that will break through the existing yield barriers without sacrificing quality or environmental sustainability. What is a “Genome”? Simply, it is all of a living thing’s genetic material, the entire set of instructions for the creation and the function of an organism. Genome sequencing is the process of determining the consecutive order (sequence) of the chemical building blocks (“bases”) that make up the DNA of each chromosome.

Why is understanding the genome sequence important? While a sequence is a powerful tool for understanding biology and is the most effective, efficient technique for identifying genes, its true power lies in the fact that it is the only platform that facilitates discovery of the entire regulatory network of developmental processes that underpin complex traits, such as yield. With genome sequences in hand, rice, maize, soybeans, and sorghum are tackling complex traits with high throughput single nucleotide polymorphism development to understand the genetic differences between varieties/hybrids and accelerated map based cloning of quantitative trait loci underlying agronomically important traits.

Despite its importance, genomics in wheat has lagged significantly behind other major crops. The multifaceted genome of wheat is extremely complex and difficult to decipher with its hexaploid nature, highly repetitive genome content, and large size (17 Giga bases, or 5-6 times that of the human and maize genomes). While this complexity enabled its success as a food crop, the full potential of genome sequencing technologies has been slow in coming to complex genomes like wheat.

The International Wheat Genome Sequencing Consortium (IWGSC: www.wheatgenome.org) was launched in 2005 with the aim of advancing agricultural research for wheat production and utilization by developing DNA-based tools and resources that result from sequencing the wheat genome. The IWGSC is an industry, academic and governmental agency collaboration at the international level with more than 150 members in 26 countries. The consortium is governed by six co-chairs (from the US, Australia, France, Japan, and Switzerland), a Coordinating Committee (CC), and an executive director. The CC consists of members involved in the development of IWGSC resources and projects or from organizations that provide direct support for the consortium. General membership is open to anyone with an interest in wheat genomics. The IWGSC establishes strategic plans, facilitates and coordinates research projects and funding efforts, develops and supports the design of research proposals, provides a framework for the establishment of common guidelines, protocols, and resources, and organizes scientific meetings and workshops.

To ensure the greatest utility for breeders, the consortium implements a milestone based strategy that delivers products and tools while working towards the ultimate goal of a high quality, reference genome sequence that will serve as the launching pad for future wheat improvement.

In following this strategy, the mid-term goals of the consortium are to develop a physical map of the 21 chromosomes of bread wheat cv. Chinese Spring that will provide a substrate for sequencing while also accelerating map-based cloning and develop new markers, enhancing our knowledge of the wheat genome organization, and permitting the assessment of sequencing technologies. To reduce the complexity of the wheat genome analysis, the IWGSC has adopted a “chromosome-based strategy” that relies on the isolation of individual chromosomes or chromosome-arms. The first pilot project, chromosome 3B, conducted at INRA Clermont-Ferrand, France, has resulted in the completion of the first physical map of a wheat chromosome. This project now serves as a model for other international groups to assemble the physical maps of the 20 other wheat chromosomes within the IWGSC. Funds have been secured to complete the physical maps for 10 other chromosomes and proposals are under development for 9 other chromosomes (see the “physical mapping graphic).

Efforts are underway now to secure funding to sequence the 3B chromosome. The IWGSC, joined by the International Barley Sequencing Consortium, held an international workshop in France this past September to develop strategic roadmaps for sequencing the wheat and barley genomes. The roadmap will be utilized for sequencing chromosome 3B. The consortium continues to seek sponsorship and funding for the physical maps of the remaining chromosomes and, as the physical maps are completed, the IWGSC will seek funding for sequencing.

To become a member of the IWGSC or to obtain more information about the consortium or its projects, please go to the website at: www.wheatgenome.org.

The IWGSC is sponsored by the Arizona Grain Research and Promotion Council, Australian Centre for Plant & Functional Genomics, Biogemma, Delley Semences et Plantes SA (DSP SA), INRA (France), the Kansas Wheat Commission, Limagrain, the Minnesota Wheat Research and Promotion Council, the Nebraska Wheat Board, RAGT Seeds, and the South Dakota Wheat Commission.

Sixty scientists from 15 countries attended a sequencing workshop held September 2008 at the French National Sequencing Center. The International Wheat Genome Sequencing Consortium (IWGSC) and the International Barley Sequencing Consortium (IBSC) organized the workshop. Gary Muehlbauer from the University of Minnesota was one of the organizers and participants.