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Cereals Introduction

Why study the Grass Family?

The grass family, Poaceae or Gramineae, has five subfamilies with approximately 10,000 species (1). Grass species can be found living in a wide range of altitudes (edge of the sea to 1000's of feet above sea level), temperatures (equatorial belt to arctic and Antarctic regions), moisture conditions, soil types and salinity concentrations (2, 3). The grass family offers many important economic and ecological features including food, forage, cane sugar, fiber (paper and rope), renewable energy, habitat, development of ecologically disturbed areas (prevention of soil erosion, extraction of salt and bioremediation), timber, lawns, ornamentals, and aromatic oils (1, 2, 3).

Cereals such as rice, wheat and maize are members of the grass family and they are particularly important to humans because of their role as staple food crops in many areas of the world. Cereals are also used to produce animal feed, oils, starch, flour, sugar, syrup, processed foods, malt, alcoholic beverages, gluten and renewable energy (4). Approximately 50% of the world's calories are provided by rice, wheat and maize, but in many parts of Africa and Asia, people rely mainly on grains such as sorghum or millet. Maize, sorghum and barley are important sources of livestock feed and barley and rice are used in the brewing industry (5). The United States Department of Agriculture recommends that Americans eat 6-11 servings of grains per day (6). Grains of all kinds, oats in particular, have been shown to contain chemical compounds that help to reduce the chance of certain types of cancer and coronary heart disease (7).

Grasses are believed to have evolved over 60-70 million years ago and the diverse members of this family vary widely in appearance, mating habit, zones of adaptation, physiology, number of chromosomes and genome size (8, 9). Despite these apparent differences, most grasses have a similar set of genes and show relative conservation of gene order along the chromosomes. For this reason, the grass research community is able to consider these species as a single genetics system (10, 11). Comparative genetics, therefore, has become an important tool for geneticists and plant breeders. A scientist who studies one species in depth can use this knowledge to predict the location and identity of genes in another, distantly related grass species (9). Researchers and breeders now have a greater range of genes and alleles to work with and are no longer confined to information gained from their own species (9, 12, 13). Insights gained from comparative genetics include how grass chromosomes have evolved, inferring the identity and composition of the ancestral grass genome and understanding how evolution has created new genotypes, phenotypes and species from the same set of genetic material (14, 15). Comparative genomics is also providing new strategies for breeding crops with improved disease and insect resistance, stress tolerance (such as drought or high planting density) nutritional quality and yield (16, 17), and also for improving the milling, brewing or oil quality of the grain, or for finding novel industrial applications (18). These comparative genomics approaches will also help with the research of "orphan" species such as oat (11) or millet (19, 20) that are not as well studied as the major crops or do not have the same kind of genetic tools available.

The sequencing of the rice genome provided the first reference genome for the grasses. Rice was selected for sequencing because of its small, diploid genome, its high gene density, the availability of high resolution genetic and physical maps, a large collection of ESTs and mutant stocks, and the large publicly available collection of rice germplasm (21, 22, 23).

Today, good bioinformatics tools are necessary to manage and exploit the vast and rapidly expanding pool of data. The Gramene database aims to help researchers and plant breeders identify and understand the relationship among genes, pathways and phenotypes in a wide range of grass species.

Plant Resources for Educators: General Biotechnology and Bioinformatic Resources:

1. Chapman, G.P, 1996. The Biology of Grasses. CAB International, UK. (Gramene Reference ID 8384)
2. Arber, A., 1934. The Gramineae: a study of cereal, bamboo, and grass. University Press, Cambridge. (Gramene Reference ID 8385)
3. Pool, R., 1948. Marching with the grasses. University of Nebraska Press, USA. (Gramene Reference ID 8386)
4. Pomeranz, Y and L. Munck, eds., 1981. Cereals: A Renewable Resource. American Association of Cereal Chemists, St. Paul, MN. (Gramene Reference ID 8387)
5. Chopra, V.L. and S. Prakash, eds., 2002. Evolution and Adaptation of Cereal Crops. Science Publishers Inc, NH, USA. (Gramene Reference ID 8381)
6. United States Department of Agriculture, 1996. Food Guide Pyramid Booklet. (Gramene Reference ID 8388)
7. Marquart, L., et al., eds., 2002. Whole grain foods in health and disease. American Association of Cereal Chemists, St. Paul, MN. (Gramene Reference ID 8389)
8. Moore, G., 1995. "Cereal genome evolution: pastoral pursuits with 'Lego' genomes." Current Opinion in Genetics and Development, v5, 717-724. (Gramene Reference ID 2911)
9. Bennetzen, J., et al., 1997. "The Unified Grass Genome: Synergy in Synteny." Genome Research, v7, 301-306. (Gramene Reference ID 5387)
10. Moore, G., et al., 1995. "Grasses, line up and form a circle." Current Biology, v5, n7, 737-739. (Gramene Reference ID 2912)
11. Van Deynze, A., et al., 1995. "Comparative mapping in grasses. Oat Relationships." Mol Gen Genet, v249, 349-356. (Gramene Reference ID 6932)
12. Gale, K., et al., 1998. "Plant Comparative Genetics after 10 years." Science, v282, 656-658. (Gramene Reference ID 6938)
13. Bennetzen, J., 2002. "Opening the Door to Comparative Plant Biology." Science, v296, 60-63. (Gramene Reference ID 6568)
14. Bennetzen, J., et al., 2002. "Numerous small rearrangements of gene content, order and orientation differentiate grass genomes." Plant Molecular Biology, v48, 821-827. (Gramene Reference ID 6834)
15. Bennetzen, J., et al., 1998. "Grass genomes." PNAS, v95, 1975-1978. (Gramene Reference ID 5390)
16. Phillips, et al., 1998. "Plant genomics and our food supply: An introduction." PNAS, v95, 1969-1970. (Gramene Reference ID 8390)
17. International Rice Research Institute, 2001. Rice Research and Production in the 21st Century. (Gramene Reference ID 8380)
18. Morris, P and J. Bryce, eds., 2000. Cereal Biotechnology. Woodhead Publishing Limited, Cambridge. (Gramene Reference ID 8391)
19. Laurie, D., et al., 2002. "Trends in comparative genetics and their potential impacts on wheat and barley research." Plant Molecular Biology, v48, 729-740. (Gramene Reference ID 6835)
20. Devos, K., et al., 1997. "Comparative genetics in the grasses." Plant Molecular biology, v35, 3-15. (Gramene Reference ID 719)
21. McCouch, S., 1998. "Toward a plant genomics initiative: Thoughts on the value of cross-species and cross genera comparisons in the grasses." PNAS, v95, 1983-1985. (Gramene Reference ID 2714)
22. Van Deynze, A., et al., 1995. "Comparative mapping in grasses. Wheat Relationships." Mol Gen Genet, v248, 744-754. (Gramene Reference ID 4733)
23. Moore, et al., 1997. "Are rice chromosomes components of a holocentric chromosome ancestor?" Plant Molecular Biology, v35, 17-23. (Gramene Reference ID 2913)