The International Rice Genome Sequencing Project (IRGSP), comprised of scientists from nine countries, unveiled the rice genome consisting of roughly 400 million DNA bases holding 37,544 genes on rice's 12 chromosomes.

This important food crop turns out to have more genes than humans, said scientists in a paper published in Aug. 11 issue of the journal Nature. Humans have only 20,000 to 25,000 genes.

"Rice is a critically important crop, and this finished sequence represents a major milestone," said Robin Buell, lead investigator for The Institute for Genomic Research (TIGER), a US participant in the rice genome group.

"We know the scientific community can use this data to develop new varieties of rice that deliver increased yields and grow in harsher conditions," he noted.

The world consumes over 400 million tons of rice every year. And over the next 20 years, world rice production must increase by a projected 30 percent in order to feed the earth's growing population, according to scientists' forecast.

This finished sequence will provide an indispensable roadmap to agricultural researchers using both biotechnology and conventional breeding to develop hardier rice varieties.

Rice is genetically similar to maize, wheat, barley, rye, sorghum, and sugarcane. Its genetic map will greatly speed scientists' hunt for genes that increase yield, protect against disease and pests, or provide drought-resistance in rice and other cereal crops, experts said.

"We can use the rice genome as a base for genomic studies of cereals," Buell said, adding that rice has a considerably smaller genome than maize and wheat, making it a better candidate for sequencing.

The rice genome is largely co-linear with other cereal genomes, a fact that means similar genes in the other plant species should pop up in roughly the same spots as their rice counterparts.

With the finished sequence, rice researchers gain a kind of "genetic GPS," while other cereal researchers inherit a hand-drawn map with some important landmarks.

In the current study, researchers compared rice to the only other fully sequenced plant genome, Arabidopsis thaliana, a leafy plant that is a popular laboratory model.

While 90 percent of Arabidopsis proteins also occur in rice, only 71 percent of rice's proteins occur in Arabidopsis. That suggests that rice may hold many rice-specific or cereal-specific genes, scientists said.

The IRGSP was launched in 1997. Scientists had aimed to finish the work by year 2008, but completed the task three years ahead of schedule.

The finished rice genome is accelerating discoveries in other areas. Scientists have used the finished sequence to identify genes that control some fundamental processes, such as flowering.

Rice's similarity to barley also has helped researchers identify genes responsible for resistance to barley powdery mildew and stem rust, two major crop diseases.

"The map-based sequence has proven useful for the identification of genes underlying agronomic traits. The (discoveries) identified in our study should accelerate improvements in rice production," scientists affirmed in the Nature article.

(Xinhua News Agency August 11, 2005)