Cottonseed, Genetically Engineered to be Edible

Cottonseed is used as cattle forage, to extract alimentary oils, which is also manufactured as margarine in the preparation of crackers, cookies and chips, but high amounts of gossypol - a very toxic compound harmful to the heart and liver - have stopped its use as a food staple. Gossypol is produced by glands in all the above-ground parts of the cotton plant.

But geneticists at Experiment Station, Texas A&M University and the U.S. Department of Agriculture's Southern Plains Research Center in College Station have engineered a strain of edible cottonseed with very low levels of gossypol. "The exciting finding is that we have been able to reduce gossypol from cottonseed to a level that is considered safe for consumption," said Dr. Keerti Rathore, plant biotechnologist. "In terms of human nutrition, it has a lot of potential."

The new seeds represent a potential high-protein food available to 500 million people annually. What is the novelty of this research is that the gossypol has been reduced only in the protein rich cottonseed, but not in the rest of the plant where it protects the plant against insects and pathogens. Cotton with no gossypol glands throughout the plant were a commercial failure as the lack of any gossypol transformed the plants into vulnerable targets for insects and diseases. Using RNAi technology, the researchers inhibited the gossypol gene only in the cottonseed, but it was left active in the rest of the plant.

"What we have done is use this technology to selectively inhibit a gene that codes for an enzyme that is involved in the gossypol biosynthetic pathway in the seed", Rathore said. Cotton has been cultivated for 7,000 years, but the seed has been edible only for ruminants like cattle, sheep, goats, which buffer gossypol in their four compartmented stomachs. "Very few people realize that for every pound of cotton fiber, the plant produces 1.6 pounds of seed," Rathore explained.

Cotton is amongst the most extensively engineered crops worldwide. "The world produces 44 million metric tons of cottonseed each year. Cottonseed typically contains about 22 % protein, and it's a very high-quality protein."

"If cottonseed were safe for human consumption, the cottonseed the world produces each year could provide the total protein requirement for a half-billion people," said Rathore. "Processes have been developed to extract gossypol, making the oil available for human consumption but at great expense", he said.

The meal left after the oil extraction still contains the gossypol and is toxic even for pigs or chickens. The new plants would make the crop more valuable both as a fiber and as a food or forage. "This discovery will yield not just one new variety, but rather a new trait that can be bred into any good commercial variety, and the trait should be maintained generation after generation," Rathore said.

In laboratory, the trait was successfully preserved through three generations. The next stage will be the cultivation of the strain in greenhouse, and spreading out the strain into commercial development will take more than a decade.