London, Sept 29 : A research team led by Penn State Distinguished Professor of Biology Hong Ma has found a new gene in rice, called GIF1, which may prove beneficial for breeding high-yield rice.
The researchers believed that the identification of GIF1 gene, responsible for the size and weight of rice grains, 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," Nature magazine quoted Ma as saying.
The scientists have revealed that they first discovered 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 team 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. 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," said He.
In order to test the ability of the GIF1 gene to control the production of invertase, the team measured the activity of invertase within a normal strain of rice, in which the GIF1 gene lacked any mutations.
The researchers did the same within a mutant strain of rice, in which the GIF1 gene contained a mutation that caused a defect in the invertase activity.
Invertase activity in the mutant strain was found to be only 17 per cent of the activity that was observed in the normal strain, which indicated that the GIF1 gene does, indeed, control invertase activity.
After that, the researchers created transgenic lines of rice, in which the GIF1 gene was over expressed. It was found that the transgenic rice had larger and heavier grains, as compared to normal strains.
The researchers were surprised to find that the GIF1 gene was so specialized in controlling invertase activity in a particular part of the grain -- the vascular tissue, which transports nutrients, including sugars generated by invertase, to the developing grain.
"The expression pattern was not expected, in part, because invertase is a general enzyme that is used by many cell types. In fact, the corresponding gene in wild rice is not expressed specifically," said Ma.
The researchers also discovered that the GIF1 gene was one of the genes selected during the domestication of rice.
"By selectively growing only those strains of rice with heavier grains, humans for thousands of years unknowingly have been increasing the frequency of rice populations that had modifications in the GIF1 gene," said Ma. "This process has caused GIF1 to be expressed specifically in the vascular tissue and, thus, to produce larger rice grains," said Ma.
The researchers believe that their findings may help others in creating hybrid varieties of rice that produce even larger grains.
They are planning to conduct further research that will help them 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.