[BEIJING] Scientists have identified a gene that contributes to the size and weight of rice grains.
Publishing their results online in Nature Genetics (28 September), the scientists — led by He Zuhua of the Shanghai Institutes for Biological Sciences at the Chinese Academy of Sciences — hope their finding can be used to improve rice yields.
'Grain-filling' — increasing the mass of rice grains — is an important trait that contributes to grain weight and therefore yield, but it is unclear which genes control the process.
The team selected rice strains that have poor grain-filling and, following extensive genetic screening, found a mutation within a gene called GIF1 (Grain Incomplete Filling 1).
According to the researchers, the GIF1 gene is responsible for controlling the activity of the enzyme invertase, which is located in the rice plant's cell walls and converts sucrose to substances that are then used to create starch.
Invertase activity in GIF1 mutant plants was around one fifth that of plants with the normal GIF1 gene. When the researchers developed a transgenic rice strain which over-expressed the GIF1 gene, the plants had larger and heavier grains than normal strains.
In their studies, the researchers also found that farmers have tried to develop rice varieties expressing the GIF1 gene during the domestication process.
"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," says co-author Ma Hong, a professor of biology at the US-based Pennsylvania State University.
The clear molecular mechanism can now be further used in cultivation. "Many rice varieties with high yield potential — including 'super-rice', usually with big panicles [large number of grains] — often suffer from bad grain filling. We believe that improvement of grain-filling, and hence grain weight, will greatly increase yield potential," He told SciDev.Net.
Separately, in the same issue of Nature Genetics, a team of Chinese scientists at the Beijing-based China Agricultural and Tsinghua universities report the molecular mechanism behind the ancient rice domestication practice of transforming limp growth of ancestral wild rice to erect growth, a critical event in rice domestication that improved plant architecture and increased grain yield.
They found that limp growth of wild rice is controlled by a gene called PROG1 (Prostrate Growth 1) and many modern rice cultivars disrupt PROG1 function and inactivate its expression, leading to erect growth, greater grain number and higher grain yield in cultivated rice.
Nature Genetics doi 10.1038/ng.220 (2008)
Nature Genetics doi 10.1038/ng.197 (2008)