Heavy rice stands tall
Genetic techniques guide natural breeding process.
Biologists say they have built a better rice plant: one that is heavy with seeds, but not so tall that it will fall over in the rain.
The work is expected to help increase yields of rice, which is the staple grain for the majority of the world's population. The many-seeded variety is less likely than others to bend double in high winds or rain, and this keeps the tops out of the water and reduces their chance of rotting.
The new plant was made possible through a mix of modern and old-fashioned techniques. First, the recent availability of the rice genome allowed the researchers to investigate areas of the plant's DNA that influence productivity. Motoyuki Ashikari of Nagoya University and Hitoshi Sakakibara of RIKEN in Yokohama, along with their colleagues, were able to determine that a gene in one particular area of DNA, for example, produces an enzyme that degrades a seed-production hormone.
If this gene isn't very active, and produces only a small amount of the enzyme, then the hormone builds up and encourages the plant to pump out more seeds. This was confirmed by genetically altering individual plants to express this gene to varying degrees.
Armed with this knowledge, the team then produced an improved variety of rice the old fashioned way - through traditional breeding. They selected two breeds: one well known for producing lots of seeds, and one that tends to be short. They then screened successive generations of rice plants for the areas of DNA they knew to influence these traits, in order to select the best plants to cross with each other. The results of four years' work in the lab and field appear online in Science1.
Cream of the crop
The researchers stress that although their plants are not genetically engineered, they believe that genetic engineering may be a useful tool to improve crop yields. "Our approach is one of the powerful methods. However it is not all-powerful," says Ashikari. Genetic engineering might one day be employed to move useful areas of DNA from rice into other crops, such as wheat and soy, they suggest.
The variety makes 25% more seeds than the popular Koshihikari type, which was one of its parents. Such high-yield plants may be in the fields in the "very near future", according to the researchers.
Susan McCouch, a rice geneticist at Cornell University in Ithaca, New York, says that rice breeders could use the information about which portions of DNA affect productivity immediately.
She adds that she is impressed with the scope of the work. "These guys screened 14,000 plants. That is a really remarkable piece of work. I just take my hat off to them."
- Ashikari M. & Sakakibara H. et al. Science, doi:10.1126/science.1113373 (2005).
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