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Genetic Map Completed, New Rice Age Dawns

August 11, 2005|Robert Lee Hotz | Times Staff Writer

Researchers have deciphered the complete genetic code of rice, accelerating efforts to improve a staple that feeds half the world, an international consortium led by Japan announced Wednesday.

Humanity has been growing rice for 10,000 years, but only now, after scientists have dissected the molecules of its creation, can farmers, who raised 880 billion pounds of rice last year, directly manipulate the blueprint of its growth and development.

There are 120,000 varieties of rice, but just two of them -- japonica and indica -- supply 20% of the world's calories, feeding more than 2 billion people in Asia alone. Demand has doubled in the last 20 years. By 2025, as many as 4.6 billion people will depend on rice for survival, experts predict.

Plant breeders already have used preliminary information from the rice genome to craft experimental strains of rice that better withstand extremes of wind and cold.

"It is catalyzing a lot of research," said one of the project's leaders, Richard McCombie at the Cold Spring Harbor Laboratory in New York. "There is a lot of pressure on breeders to improve the crop, and this is a valuable tool to do that."

All told, it took researchers at 32 centers in 10 countries eight years to completely document and map the spiral chain of amino acids that encodes the life cycle of the rice plant.

Rough drafts of the japonica and indica genomes, developed by a San Diego-based research group and a consortium in China, were released in 2002.

In research published today in the journal Nature, they reported that nature takes only two-thirds as many genes as scientists once predicted to create a rice plant, but even so, thousands more than required to make a human being.

The japonica strain of rice, the researchers discovered, contains 37,544 genes spelled out in 389 million chemical letters of DNA packaged in 12 chromosomes, compared with about 20,000 known genes in the 24 chromosomes of the human genome.

More than 2,800 genes appear to be unique to rice, the scientists said.

At a time when researchers are quick to treat genetic information as a proprietary trade secret, the consortium is making its rice genome data freely available to researchers.

"Knowing the sequence of one of the world's most important crops will be invaluable to plant genomics researchers," National Science Foundation Director Arden L. Bement Jr. said. "This project will potentially help millions of people around the globe."

The completed rice genome will be "indispensable" in the effort to boost harvests to meet a global appetite expected to grow 30% over the next 20 years, said Takuji Sasaki, vice president of the National Institute of Agrobiological Sciences in Tsukuba, Japan, the senior scientist in charge of the International Rice Genome Sequencing Project. The completed genome, he said, is "the gold standard" against which different genes controlling taste, flowering, nutrition, health and growth culled from different rice varieties can be located, compared and explored.

"Now we can get the most fundamental information about the [genetic] inheritance of rice plants," Sasaki said.

With the advantage of insights from the new genome sequence, researchers trying to improve crops can conduct experiments in 20 minutes that might have taken two years with conventional techniques, the scientists said.

"This could accelerate breeding programs," said molecular biologist Joachim Messing at Rutgers University in New Jersey, who also participated in the project. "You will not only save time in generating plants, but you will be able to be more targeted."

Moreover, because rice is the first cereal crop to be fully analyzed, researchers expect that such intimate knowledge of its genetics will unlock the heredity of more complex grains, including corn, wheat and barley.

"Rice is the Rosetta stone for crop genomes," said Robin Buell, who led the rice sequencing effort at the Institute for Genomic Research in Rockville, Md. "We can start to ask what makes a cereal a cereal."

The structure of the rice genome itself also may offer a fundamental insight into the difference among all plants and animals, Messing said.

The genomes of mammals such as mice, men and rats are all about the same size. In contrast, plant genomes vary widely. Rice is three times the size of the common Arabidopsis plant, a member of the mustard family often used as a laboratory standard, but only one-seventh the size of the corn genome. The wheat genome is 41 times bigger than the rice genome.

Overall, more than a quarter of all rice genes cluster into families closely related by function and chemical sequence, "like ducks sitting next to each other," Messing said.

No one is certain why. It may mean that plants evolved a greater need for backup copies of important genes.

"This could be a profound difference between plants and animals," Messing said. "Plant genomes may make more backups of genes."

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