Sequencing of the rice genome not only opens up a vast reservoir of biological information but also promises to benefit the production of cereal crops, which make up about 60 percent of the world's diet, according to a researcher at the University of California, Davis.
Completion of the sequencing of the rice genome will be announced in the April 5 issue of the journal Science. It is the first complete genome sequencing of a crop plant.
The Science papers on the sequencing work are accompanied by a commentary written by Pamela Ronald, a UC Davis molecular biologist and an authority on rice genetics. In 1995 Ronald isolated the first disease-resistance gene in rice.
"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," writes Ronald.
The sequencing was done by two research groups, one from the Swiss-based agrochemical company Syngenta International and the other from the Chinese Rice Genome Research Program.
The Chinese group sequenced the genome of Oryza sativa indica, the most widely grown strain of rice in China.
The Syngenta research group sequenced the genome of the japonica rice strain. Genome information on that strain will be archived in a proprietary database.
In her commentary, Ronald stresses the significance of the rice genome sequencing for feeding a world that faces both a growing global population and a decline in productive farmland.
She points out that global cereal yields must increase 80 percent over the 1990 average in the next 20 years just to keep pace with increases in global population. The continuing loss of farmland due to urban development and degradation of agricultural soils makes this challenge even more difficult.
Sequencing of the rice genome is especially valuable because rice is the model plant for studying other important grain crops, including wheat, barley and corn.
Furthermore, Ronald points out, researchers can now compare the genomes of plants representing the two major groups of flowering plants: the grasslike monocotyledons, like rice and corn, which grow from single-leafed seedlings and the dicotyledons, like beans, which grow from two-leafed seedlings.
Scientist also now can look for the function of a particular rice gene by comparing it with the genomes of nonplant organisms, such as the drosophila fly, nematode and even humans.
"Comparative genomic analysis enables biologists to assign a tentative function to a gene according to what that gene does in another species," she writes. "Genes controlling disease resistance, tolerance to abiotic stresses or synthesis of essential vitamins can also be predicted by comparative genome analysis."
Plant researchers will now be able to better understand how genes function in crop plants and develop hardier and more productive varieties by introducing genes with desirable traits using traditional breeding or genetic engineering, she says.
"Finally, knowing the sequence of specific genes will allow us to tap into the natural genetic variation of crop species," writes Ronald, noting that more than 100,000 specimens of traditional rice varieties and wild rice species have been collected and are maintained at the International Rice Research Institute Genebank. The genome sequencing data will enable researchers to identify genes from those seed specimens that have agricultural importance.