Gossypol is a toxic compound that occurs throughout the cotton plant and protects it from pests. Researchers from Texas Agricultural Experiment Station at Texas A&M University and the USDA’s Southern Plains Research Center in College Station, PA have modified cotton plants via RNAi to achieve a plant that has gossypol-free seeds, suitable for human consumption.
Press office from Texas Agricultural Experiment Station dreams of gossypol-free high-protein burgers:
Gossypol naturally occurs within the glands in all the above-ground parts of the cotton plant including the seed. Rathore said the “beauty of this project” is that the gossypol has been reduced only in the cottonseed — where the high levels of protein are packed — but not in the rest of the plant where the compound serves as a defense against insects and disease.
The team used RNAi, or technology that can “silence” a gene. This enabled them to target the gossypol gene only in the cottonseed but let the gene express itself in the rest of the plant. The discovery of RNAi is what landed the Nobel Prize for Medicine this year for U.S. scientists Andrew Z. Fire and Craig C. Mello.
“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. [Dr. Keerti Rathore, a plant biotechnologist –ed.]
Cotton fibers have been spun into fabric for more than 7,000 years. For most of that time, products from the fuzzy seed that is extracted in the fiber process have been edible only for cattle. They can tolerate gossypol only after digesting it through the four compartments of their stomachs.
“Very few people realize that for every pound of cotton fiber, the plant produces 1.6 pounds of seed,” Rathore pointed out. “The world produces 44 million metric tons of cottonseed each year. Cottonseed typically contains about 22 percent protein, and it’s a very high-quality protein.”
In all, about 10 million metric tons of protein are contained in that amount of seed, he said.
Decades ago, California and Texas researchers were able to breed cotton varieties that contained no gossypol glands throughout the plant. But glandless varieties were a commercial failure, Rathore said, because the lack of any gossypol made the plants a delicious treat for insects and diseases.
Processes have been developed to extract gossypol, making the oil available for human consumption but at great expense, he said. Plus, the meal that is left after the oil is removed still contains the gossypol and thus is not edible for humans, or for pigs, chickens or turkeys.
Plants with the new trait developed by the team could make the plant more valuable both as a fiber and a food crop.
“One could utilize the cottonseed either directly as food if there is no gossypol or as feed for livestock,” he said.
The food value of the cotton crop may be for countries “where there are small farmers who grow cotton, and if they could use the seed they could get much more value from it,” Rathore noted.
He believes food products ultimately could be developed from the cottonseed of these new plants. Though the glandless cotton varieties bred by Experiment Station researchers in the late 1970s and 1980s suffered from insects and disease, one of the food products — TAMUnuts — made from the seed of these plants could be eaten by humans.