WASHINGTON, Sept. 29 (Xinhua) -- A team of scientists from institutions in the U.S. and China have identified a gene in rice that controls the size and weight of rice grains.

The gene may prove to be useful for breeding high-yield rice and, thus, may benefit the vast number of people who rely on this staple food for survival.

"Our work shows that it is possible to increase rice's yield by enhancing the expression of a particular gene," said Hong Ma from Pennsylvania State University. The team's results were published Monday in an early online edition of the journal Nature Genetics.

The researchers first searched for and identified mutant strains of rice that exhibited underweight grains. "We found a particular mutant that is defective in its ability to produce normal-sized grains," said Zuhua He, a biology professor at the Chinese Academy of Sciences and the leader of the team.

The group then examined the mutant and found that it carried a mutation within the GIF1 gene. "The GIF1 gene is responsible for controlling the activity of the enzyme invertase, which is located in the cell wall and converts sucrose to substances that then are used to create starch," said He.

"Invertase is important in the formation of starch within developing grains of rice. If invertase is not active, the rice plant cannot produce edible grains."

They tested and found that invertase activity in the mutant strain was only 17 percent of the activity that was observed in the normal strain, suggesting that the GIF1 gene does, indeed, control invertase activity. The team then created transgenic lines of rice in which the GIF1 gene is over expressed and found that, compared with normal strains, the transgenic rice had larger and heavier grains.

The scientists hope that their findings will help others to create hybrid varieties of rice that produce even larger grains. In the meantime, they plan to perform additional analyses that will help them to understand how other genes might be involved in the process of improving rice yield.

"The goal is to understand what controls grain weight and other factors, and to look for ways to increase yield," said Ma.
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