November 20, 2006
National Geographic News
A toxic chemical has been mostly removed from cottonseeds, potentially turning an underused agricultural product into a food source for hundreds of millions of people, according to a new study.
"The world grows cotton for fiber not for seed," said Keerti Rathore, a researcher at Texas A&M University in College Station who helped spearhead the work.
"Few realize, however, that for every pound [0.45 kilogram] of cotton fiber, the cotton plant produces 1.65 pounds [0.75 kilogram] of seeds that contain 21 percent oil and 23 percent of a relatively good quality protein."
Some 48.5 million tons (44 million metric tons) of cottonseed are produced annually, much of it by 20 million farmers in Asian and African countries with high rates of malnutrition and starvation, the study authors write .
But nutrient-rich cottonseeds are unfit for human consumption because of a noxious chemical called gossypol, a toxin with properties that keep bugs at bay and cause health problems in humans and many animals.
Currently cottonseeds are used to make feed for cows, which can handle gossypol, thanks to special microbes in their stomachs.
But now the research team has found a way to genetically engineer cottonseeds that barely produce gossypol, possibly making the seeds fit for human menus.
"Global cottonseed production can potentially provide the protein requirements for half a billion people per year," the team reported in tomorrow's issue of the Proceedings of the National Academy of Sciences.
It's a Knockout
Researchers have long wrestled with the problem of cottonseed toxicity, says Danny Llewellyn, an Australian expert in cotton genetics who was not involved in the study.
Initial efforts were aimed at creating toxin-free seeds by crossing cultivated cotton with wild cotton plants that produce more gossypol in their leaves and less in their seeds.
But those tactics failed, because the genomes of wild and domestic cottons are too different.
The recent research used a technique called RNA interference (RNAi) to suppress the biochemical pathways that produce gossypol in cottonseed tissue (learn more about RNAi and how it was discovered).
The team created a hybrid gene that was then driven by a "seed promoter"—a natural device that guides genetic expression and that, in this case, limited the effects of the genetic tinkering to the seed only.
The process rendered cottonseeds with 98 percent lower levels of gossypol while leaving levels of the toxin in other parts of the plant untouched.
"The RNA mechanisms only work on the seeds, so that the leaves still contain gossypol and discourage insects from chewing them," study co-author Rathore said.
"If you knock it out throughout the plant, [the cotton] is more susceptible to diseases."
According to Llewellyn, Rathore's study represents the first substantiated case where gossypol was reduced via genetic engineering that targets the genes that make the toxin.
The new study could have a large impact on global food security if the technique can be reproduced and cottonseeds are approved for human consumption.
A "gossypol-free cottonseed would significantly contribute to human nutrition and health, particularly in developing countries, and help meet the requirements of the predicted 50 percent increase in the world population in the next 50 years," the report authors wrote.
Llewellyn, the Australian cotton researcher, says that developed countries will likely keep using cottonseeds for animal feed and food oils.
"But there will be some interesting uses of the meal potentially as a substitute for soybeans," he said.
Deborah Delmer, associate director of food security at the Rockefeller Foundation in New York City, agrees.
"If these transgenics really pan out in future extensive field trials as being truly gossypol-free in the seed, and the RNA approach remains stable over a number of generations with no affect on fiber yield, then such plants could well enhance the value of cottonseed meal considerably," she said.
Making cottonseeds a more direct source of human food could also save energy and resources.
Study co-author Rathore said that "feeding it to cows is not the most efficient use of a valuable source of protein.
"It takes 6 pounds [2.7 kilograms] of feed to convert to 1 pound [0.45 kilogram] of meat. [Cows] are inefficient converters."
And the researchers' technical success raises hopes that noxious chemicals in other foods can be reduced via similar methods.
"Traditional foods such as cassava and fava beans could also be made safer for consumption … ," the report authors wrote.
Cassava and fava beans contain low levels of toxins and can cause human health problems when eaten raw or undercooked. Proper cooking neutralizes the threat.
Rathore says his team is working to ensure the technique is replicable.
"We want to make sure it is stable," he said. "So we will test more generations in the greenhouse and do field studies to make sure it works the way it is supposed to."