Toxin Buster: New technique makes cottonseeds edible

Scientists have engineered cotton plants to produce seeds that are missing a poisonous compound that had previously rendered them inedible. With the amount of crop currently planted, such modified cottonseeds could fill the daily protein needs of about 500 million people, the researchers say.

SPOT THE TOXIN. Gossypol-secreting glands form dark spots in seeds from normal cotton plants (top). Seeds from engineered plants (bottom) are missing the dark spots and the toxic compound. PNAS

For every kilogram of fiber, commercial cotton plants produce about 1.65 kg of seeds. Though these seeds contain much high-quality protein, “right now, that’s being wasted,” says plant geneticist Keerti Rathore of Texas A&M University in College Station.

Like other parts of the cotton plant, cottonseeds harbor the compound gossypol, which is toxic to people and many other animals. Seed processors remove gossypol from cottonseed oil. However, the toxic compound is difficult to extract from the solid parts of the seed, which contain potentially useful protein.

In the 1960s, researchers discovered mutant cotton plants that didn’t produce gossypol. But since the compound protects plants from insects, the plants were vulnerable to infestations and ended up a commercial failure.

Now, Rathore and his colleagues have used a technique called RNA interference (SN: 7/2/05, p. 7: Available to subscribers at Sound Off) to eliminate gossypol only in cottonseeds. The team worked with a gene that encodes a small piece of RNA that matches another RNA piece required for making gossypol. The researchers predicted that the two RNA strands would fuse, beginning a complex cellular process that prevents cells from producing the toxin.

The team inserted this RNA-making gene next to a piece of cotton-plant DNA that activates genes only in seeds, so gossypol production would continue elsewhere in the plants.

When the scientists grew the engineered plants, they looked for the dark-colored gossypol glands typically present throughout normal cotton plants. The engineered plants had these glands everywhere except in their seeds. Chemical tests showed that the new seeds had only 2 percent as much gossypol as normal cottonseeds do. This reduced amount is considered safe by the U.S. Food and Drug Administration.

The scientists report their finding in the Nov. 28 Proceedings of the National Academy of Sciences.

Rathore says that nobody on the team has yet eaten any of the seeds. “Our seeds are extremely precious, and we didn’t want to waste any until we produced enough. When we bulk up our seed stocks, I’ll be the first person to try [eating] them,” he says.

Andrew Jordan, who is vice president of technical services for the Memphis, Tenn.–based National Cotton Council, calls the team’s accomplishment “potentially very important.”

Developing cottonseeds that don’t contain gossypol is “a topic that we’ve established as a research priority. It looks like this group has finally found a genetic solution to address this industry problem,” he says.

Jordan notes that since cotton is frequently grown in developing countries, where dietary protein can be scarce, the new seeds could offer “an important protein source for many, many people.”