The rice genome. The most precious things are not jade and pearls.

T he most precious things are not jade and pearls but the five grains. " The five grains referred to in this Chinese saying are most likely to be rice, wheat, millet, sorghum, and maize (1). These cereal grains account for up to 60% of the calories consumed by people in the developing world (2). We could also apply this saying to the valuable genetic information that cereals contain—especially rice. With a genome significantly smaller than those of other cereals, rice is an excellent model for genetic and molecular studies (3). The publication of draft genome sequences of two major subspecies of rice (indica and japonica) on pages 79 and 92 of this issue (4, 5), provides a rich resource for understanding the biological processes of plants and promises to positively impact cereal crop production. If the world's population continues to grow as predicted for the next 20 years, global cereal yield must increase 80% over the 1990 average to feed these additional people (6). Compounding the problem is that areas of productive farmland continue to be lost through urbanization and degradation of existing agricultural soils (7). Although achieving food security will require a multitude of social and economic solutions, the new knowledge derived from genomics research will make an important contribution. The challenge ahead for the plant research community is to design efficient ways to tap into the wealth of rice genome sequence information to address production constraints in an environmentally sustainable manner. Taxonomically, all cereals belong to one of the two major groups of flowering plants: the monocotyledonous plants (monocots). Completed in 2000, the genome sequence of the weed Ara-bidopsis thaliana provided our first complete view of the genome of a dicotyledonous plant (8). With the availability of the rice genome sequence , we can now directly compare the genome of a monocot to that of a dicot and to genomes of other sequenced organisms. A significant observation is that over 80% of Arabidopsis genes have close counterparts (ho-mologs) in rice whereas only 50% of rice genes have homologs in Ara-bidopsis, suggesting that all rice genes are essentially a super-set of Arabidopsis genes (4). Furthermore, at a significant level of similarity, 85% of proteins examined in cereals have a related protein in rice (3). This observation poses some interesting questions regarding what the additional rice genes do. Assuming functional conservation, the extensive DNA sequence similarity between rice and …