Genetics, Vol. 168, 583-584, October 2004, Copyright © 2004
doi:10.1534/genetics.104.036731

Genomic Resources

Moving Wheat Into the Mainstream in Plant Genomics

J. Perry Gustafson^*, Patrick E. McGuire and Calvin O. Qualset

^* USDA-ARS Plant Genetics Research Unit, Department of Agronomy, University of Missouri, Columbia, Missouri 65211
Genetic Resources Conservation Program, University of California, Davis, California 95616

GENOME analysis was used in the 1950s to establish the evolutionary and homoeologous relationships of the chromosomes of the three genomes (AA, BB, and DD) of hexaploid wheat (Triticum aestivum L.). Each of the 21 chromosomes was identified and characterized by SEARS (1954)(1966) with respect to genomic and homoeologous relationships. A vast array of genetic resources developed by Sears and many others includes monosomic, nulli-tetrasomic, ditelosomic, and terminal deletion stocks.

When molecular mapping became a reality these stocks were used to great advantage to complement hybridization-based segregating populations for recombination mapping. The need for public maps and genetic stocks became an urgent matter in 1989 and an international effort, the International Triticeae Mapping Initiative (ITMI), was launched to assure that maps would be available as a public good. Mapping using restriction fragment length polymorphisms (RFLPs) was conducted by scientists in several countries, anchored by one dominant mapping population (see summary in MCGUIRE and QUALSET 1997). While RFLP mapping provided chromosome location and interlocus relationships, physical mapping was not possible. In the meantime, it became clear that resources, such as expressed sequence tags (ESTs), for functional genomics were the next critical need. Thus, ITMI spawned another volunteer effort, the International Triticeae EST Cooperative (ITEC), whereby developers of ESTs would pool and share them for common good. This was successful in producing some 24,000 ESTs. Next, a group of U.S. scientists took ITEC to the next stage by proposing large-scale development of ESTs and mapping unigenes to chromosome bins defined by a set of deletion stocks. This project "The Structure and Function of the Expressed Portion of the Wheat Genomes," known as wEST, was funded by the NSF Plant Genome Research Program along with support from the collaborating institutions. This effort engaged the participation of 14 investigators at 10 institutions who had defined functions: cDNA library development, EST production, deletion stock characterization (QI et al. 2003) and mapping, and coordination of individual chromosome maps. The project followed the commons-based strategy outlined by BENKLER (2004) for peer production of a public good. The EST clones are available from the Wheat Genomics Resource Repository (USDA and University of California, Davis, http://wheat.pw.usda.gov/wgc/, and the Arizona Genomics Institute, http://genome.arizona.edu). No intellectual property rights were assigned to the ESTs. Project investigators and the international scientific public are free to use the ESTs for gene discovery and utilization. Discoveries emanating from specific ESTs may be subject to IPR, depending on the investigators' institutional policies.

The 10 articles that follow this Foreword provide documentation for the development of a substantial genomics resource base for wheat: (1) 37 cDNA libraries capturing a large portion of genes expressed during wheat plant development, (2) a collection, database, and analysis tools of more than 100,000 ESTs, and (3) a database of some 8000 deletion-mapped ESTs. These data have already been used by project scientists to assess wheat-rice comparative synteny (SORRELLS et al. 2003) and analysis of the organization of wheat chromosomes and their evolution (AKHUNOV et al. 2003a,b). The project provided training opportunities for approximately 160 high school, undergraduate, graduate, and postdoctoral scholars who contributed to the success of the project. The project's ESTs were the first large-scale public wheat ESTs (amounting to about 25% of the international NCBI inventory of wheat ESTs at the end of 2003) and stimulated other wheat sequencing and mapping efforts worldwide. This resource is being used by geneticists in the United States and abroad as a source of genes for high-resolution mapping of wheat chromosome regions, marker-assisted selection, comparative genomics, and a systematical survey for single-nucleotide polymorphisms to convert them into polymerase chain reaction-based markers to maximize their utility for improving our understanding of this polyploid species and to improve world food production.

View larger version (69K): In this window In a new window Download PPT slide   Spike of hexaploid wheat cv. "Chinese Spring," the genotypic background for most of the wheat aneuploid stocks, superimposed over a meiotic metaphase I spread of chromosomes from a wheat aneuploid. With permission from Gordon Kimber.