November 26, 2002

C.U. Engineers New Rice Strain

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Cornell scientists announced today that they have developed a method to improve the resilience and yield of rice — a crop that feeds over half of the world’s population, according to a report in today’s issue of the Proceedings of the National Academy of Sciences.

By adding a single gene to the common rice plant, the researchers created a crop that has the potential to grow more quickly than other rice under normal conditions and is more tolerant of chilling temperatures, drought conditions and high water salinity.

“The goal of this work was to make rice plants that were more tolerant of environmental stress,” said Research Associate Ajay Garg, molecular biology and genetics, lead author of the study. “We tested drought stress, chilling, and salt stress and found a number of plants that show substantially increased tolerance.”

This research could generate new varieties of rice that can be grown in a wider range of temperatures and in brackish water. These varieties could also produce more grain per plant under the more hospitable conditions in which rice is now grown, Garg said.

“This increases the area where rice can be grown. The plants will also tolerate water loss. They won’t grow without water but they will resume growing once the water has returned,” said Prof. Thomas Owens, plant biology.

Of the world’s 130 million hectares of land where rice is grown, about 30 percent contain enough salt to either stunt rice yields or prevent cultivation altogether. Another 20 percent of this land is periodically subject to drought conditions that routinely affect food production.

About 10 percent of locations where rice is grown occasionally experience temperatures that are too low for healthy plant development. The rice yield starts to diminish when the temperature is 15 degrees Celsius or below, but the transgenic plants produce normal yields at these temperatures.

“In principle, this same technique can be used to transform other major cereal crops such as corn and wheat, also providing them with increased resistance to stress,” said Project Leader Prof. Ray Wu, molecular biology and genetics.

Rice, along with corn and wheat, accounts for 70 percent of the calories consumed by the human population. With experts projecting a doubling of the population over the next century, transgenic crops such as these could help agriculture keep up with demand.

The genetically engineered plants produce a sugar called trehalose, which increases tolerance to adverse conditions. In invertebrates, bacteria and yeast, trehalose acts to preserve organisms in the absence of water.

“Since trehalose protects so many organisms from environmental stress, the goal was to make more of it in rice,” Owens said.

Brine shrimp eggs, commercially marketed as fish food or as pet “sea monkeys,” can remain dried up for years in a state of suspended animation due to their trehalose content. The resurrection plant, found in desert environments, can also remain in a dry, suspended state due to the presence of this sugar.

“We have designed the experiment so that the trehalose gene turns on when there is a stress. In the past, people have inserted the gene so that it is turned on all the time, which stunts the growth of the plants. Since the genes are only induced to turn on when there is a stress, the plants grow normally and become more stress tolerant,” Wu said.

The lab has experimented with six different genes, each of which provides some degree of stress tolerance. “What is special about the gene used in this case is that the degree of protection from stresses has been much higher than with the other genes that we have tested,” Wu said.

In addition to the expected increase in resilience due to the addition of the sugar, the researchers made a discovery they were not anticipating. The modified plants also exhibited higher levels of photosynthetic activity.

“Humans have been breeding plants for 5,000 years. One goal has been to produce more yield by allocating more resources to producing fruit or grain. Another goal has been to increase photosynthesis, which has been difficult to achieve even with genetic engineering. Now it appears we have found one way to do so,” Owens said.

A crop with an elevated photosynthetic rate grows faster and produces more seeds, for example more rice grains, per plant.

“We accidentally stumbled on something we didn’t expect,” Owens said. “We’ve only uncovered the grossest characteristics of this. We don’t really understand the mechanism.”

Owens hopes that further research will lead to a more thorough understanding of how the photosynthetic rate is increased.

Meanwhile, other research interests are beginning to pay off as well.

“We’ve done additional work with another gene that enhances rice yield,” Garg said. Although results are preliminary, this research could provide scientists with additional insights as to how food production might be boosted.

In the shorter term, crops more resilient to environmental conditions would be less susceptible to short-term drought and off years, thus stabilizing the food supply and commodity markets.

“A limiting factor is acceptance of genetically modified crops as a food source. As we saw with golden rice, these things don’t always make it to the people who they are intended to help,” Owens said.

Golden rice was developed in 1999 by scientists in Switzerland and Germany as a means of supplementing the diets of those in developing countries with beta-carotene, a precursor to vitamin A. Beta-carotene provides the rice with the “golden” tint from which its name is derived.

According to the World Health Organization, millions around the world suffer from blindness and early death due to vitamin A deficiency, but the technology has not yet made it to the field.

“I think golden rice was the first test system. Hopefully in a year or two, many of the legal considerations and other problems related to this will be resolved through the golden rice issue,” Wu said.

Environmentalist groups and others have opposed the plant due to its genetically engineered origin. However, as these issues are being resolved, golden rice may pave the way for other transgenic technologies.

“Humans react to things in crisis mode, so if food is not a problem for the majority of people with money, then there’s no rush to apply this technology,” Owens said.

When the technology makes it to the field, a journey that is expected to take at least three years, it will be made available freely to farmers in developing countries, Wu said. Commercial farmers in rich countries will have to go through the normal channels and pay the appropriate licensing fees.

“Our research is for humanity and global food security,” Garg said.

The six-year project was funded largely by the Rockefeller Foundation. The findings are published in today’s issue of the Proceedings of the National Academy of Sciences.

Archived article by Philip Lane