In what could herald the start of a second "green revolution," plant scientists in the United States and China have identified nearly all the genes in rice a food staple for more than half of the world's 6.2 billion people.
The results, considered rough drafts of the rice genome, represent the first time the genes of an important crop has been sequenced. Armed with this new information, which will allow researchers to begin to identify the genes' functions, scientists say they expect to shorten the time it takes to develop more-nutritious rice strains that are better equipped to weather a drought and fend off disease.
Because rice is closely related to other key cereal grains, such as maize, wheat, millet, and sorghum, information gleaned from the rice genome also is expected to lead to more-rapid improvements in these cereals. Together with rice, these cereals account for as much as 60 percent of the calories consumed by people in developing countries, according to the UN Food and Agriculture Organization (FAO).
"This is a very significant milestone," says Jeffery Bennetzen, a plant geneticist at Purdue University in West Lafayette, Ind. Beyond the potential for developing new strains of rice, he continues, "this opens the door to comparative plant science."
The publication of two rough drafts of the rice genome in today's edition of the journal Science comes at a time when the FAO experts forecast that, in the next two decades, cereal production must rise by 80 percent over 1990 levels to meet global needs.
Population growth, coupled with the increasing amount of farmland being lost to urbanization and the high cost of fertilizers and other inputs "dictate that we have to look at genetic potential as one of the most important factors in achieving higher, more stable, and sustainable yields," says Joel Cohen, a research fellow in biotechnology at the International Food Policy Research Institute in Washington.
The interest in unravelling the genome grew in the '90s as scientists discovered the key role rice could play in unraveling the genetic secrets of other cereals.
One team of researchers, led by Jun Yu of the University of Washington's Genome Center and the Beijing Genomics Center, tackled a rice strain known as indica. The team's effort covers an estimated 92 percent of the strain's genome.
The second team, led by Stephen Goff, with Swiss-based, biotech-company Syngenta's Torrey Mesa Research Institute in La Jolla, Calif., built its sequence from a rice strain more prevalent in drier climates. Known as japonica, the subspecies holds an estimated 32,000 to 50,000 genes. The Syngeta team claims its sequence covers some 99 percent of the strain's genome with 99 percent accuracy.
Work on these two sequences has accelerated international efforts to produce a complete sequence of the rice genome by the International Rice Genome Sequencing Project. Originally scheduled for completion in 2008, the project will complete its draft by the end of this year.
The techniques that project members are using will allow them to achieve higher accuracies than those achieved by the two teams who published their results today, researchers say.
Despite the gaps and inaccuracies in the two new rough drafts, the data already are being tapped by research teams worldwide. Indeed, the Chinese group made its data available to the research community on the World-Wide Web earlier this year, according to Pamela Ronald, a plant pathologist at the University of California at Davis.
She notes that her lab had been trying to locate rice genes responsible for conferring disease resistance. She had mapped the gene to a lengthy segment of DNA and had started the laborious process of sequencing the segment. "Now we can put the sequence together from publicly available data," she says.
Purdue's Bennetzen dubs the process "clone by phone."
The research community has unrestricted access to the Chinese group's data and will have similar access to the IRGSP's data. But, for all the enthusiasm about the drafts, plant biologists acknowledge that sequencing is only a first step in using the tools of biotechnology to improve cereal crops. The genes in the sequence must be mapped to specific chromosomes, their functions must be identified, as well as the processes they trigger.
Noting the reluctance of Asian and African nations to embrace food crops modified through gene-splicing techniques driven in large part by resistance that has emerged in Europe to genetically modified foods researchers say that initial benefits from rice sequencing efforts and related work in other cereals may come through traditional crossbreeding, which becomes more efficient when genomic information is used.
A clearer picture of the mix of desirable and undesirable genes in a plant, for example, will help breeders weed out strains they otherwise might have included in their crossbreeding efforts.