Researchers have developed a new strain of rice with the potential to feed a burgeoning global population while reducing the greenhouse-gas emissions rice paddies generate.
They have coaxed the rice into growing more and larger grains. At the same time, the genetic change cut methane emissions from paddies growing the rice by more than 90 percent compared with paddies growing unaltered plants.
By some estimates, rice farming may be the single largest source of methane emissions humans deliver to the atmosphere, though estimates vary widely.
Scientists have been working to develop rice with higher-nutrition, low-emissions traits for years, given that the crop that plays such a significant role in the diets of some 3 billion people.
These new results represent "the first example, to our knowledge, of such a rice," the team of scientists from China, Sweden, and the United States writes in its formal report on the effort, appearing in Thursday's issue of the journal Nature.
"The new rice sounds like a win-win for good yields and reduced climate impact," writes Paul West, lead scientist for the Global Landscapes Initiative at the University of Minnesota's Institute on the Environment, in an e-mail.
But the nature of the new rice could trigger push-back from groups opposed to genetically modified organisms, suggests Dr. West, who did not take part in the study. It was created by adding a gene taken from barley to the genome of a widely used type of rice, known as Nipponbare.
At the least, the new strain could be one more tool farmers and sustainable-agriculture advocates can use to reduce methane emissions while growing such an important staple. Others include increasing yields, which helps the amount of land used for rice farming to stay stable even as demand increases; eliminating rice "straw" from flooded fields, which can feed soil microbes that generate the methane; and either reducing the amount of water in paddies or changing the flooding schedule to allow paddies to dry out briefly at least once as the rice grows.
These approaches can be expensive or impractical, researchers say. Hence the desire to explore new rice strains.
The work began several years ago with a group of researchers at the Swedish University of Agricultural Sciences in Uppsala, says Christer Jansson, who headed the effort at the time. The scientists were trying to understand the genetic machinery that controls how carbon – in the form of sugars, starches, and other carbohydrates – is distributed in plants as they take up as carbon dioxide via photosynthesis.
The team found three types of genes that act like master switches controlling the distribution of carbon in barley. The researchers homed in on one in particular, which they labelled SUSIBA2, explains Dr. Jansson, currently director of plant sciences at the US Department of Energy's Pacific Northwest National Laboratory.
Other researchers noticed that rice plants that have the largest number of grains produce the least amount of methane. The reason: More carbon going into rice grains left less carbon to go elsewhere – like to the roots, which ultimately feed microbes that produce methane.
In modeling how the gene SUSIBA2 worked in barley "we realized it would be possible to control carbon allocation in rice," Jansson says, creating "a win-win situation. We would get more starch, more food, and less methane."
Tests and field trials in China found that the SUSBIA2 gene indeed channeled carbon mainly to the rice plants' stems and grains, according to the new study's team, headed by Chuanxin Sun at the Institute for Biotechnology at the Fujian Academy of Agricultural Science in Fuzhou, China.
This redirection of carbon reduced the amount of carbon available to methane-forming microbes in the roots and adjacent soil, reducing the number of microbes and hence methane emissions.
While SUSIBA2 rice shows promise, it could run into opposition from groups opposed to genetically modified organisms.
A decade ago, opposition erupted over Golden Rice, a variety genetically engineered to produce the precursor compounds to vitamin A. It was developed as a way to combat vitamin A deficiencies in children in developing countries, and it garnered a humanitarian award this year from the United States Patent and Trademark Office. But opposition remains.
One possible mitigating factor for SUSIBA2 rice could rest in the barley genes the team used. Golden Rice added a comound not usually found in rice – namely, beta-carotene. In SUSIBA2 rice, the introduced genes alter the distribution of carbon within the rice plants.
Even so, this redistribution could have unintended consequences, suggests Paul Bodelier, a researcher in the department of microbial ecology at the Netherlands Institute of Ecology in Wageningen.
For instance, less carbon in the roots could affect the mix of other microbes either beneficial or harmful to rice, he writes in an analysis of the results that accompanies the formal description of the work in Thursday's issue of the journal Nature.
Still, Dr. Bodelier terms the work groundbreaking. And Jansson notes that the team is tackling the question of potential effects on microbial communities surrounding this new strain of rice.
Assuming all research goes well, the rice still might not be available for quite a while, given the regulatory processes involved, Jansson adds.