Small difference factored big in rice domestication.

A change in a single position of a rice plant's genetic code lets it hold onto grains until harvest, new research suggests. The finding may give scientists new insights into how people domesticated rice, a food eaten daily by about half the world's population.

Unlike its wild-grass relatives that scatter seeds readily once they ripen, rice plants keep a firm grip on their seeds after they mature. This process enables rice farmers to collect grains easily to replant or process into food.

Scientists have long known that the capacity to retain grains played a pivotal role in rice domestication, says Tao Sang, a plant geneticist at Michigan State University in East Lansing. However, the genes controlling this phenomenon remained a mystery.

To investigate, Sang and his colleagues compared segments of rice's DNA with those of several of its wild relatives. The researchers homed in on a single gene on the plants' chromosome 4. In this gene, the researchers noticed a small difference in the sequence of DNA subunits, which go by the letters A, C, T, and G. In one location where the wild relatives have a G, domestic rice has a T.

After the researchers genetically engineered the rice to have a G in that location, their plants released their seeds easily, as their wild relatives do. The researchers report these results in an upcoming Science.--C.B.