Eliminating Gossypol From Cottonseed Using RNAi Could Provide Significant Edible Protein for Africa.

Poverty and malnutrition are widespread in Africa. In West African countries, cotton is an important cash crop. Cotton produces 1.5 times as much seed as lint, but use of the seed is restricted by gossypol, a toxic terpenoid. The elimination of gossypol from the seed could provide about 57 kilograms of edible protein per acre-year, enough to supply 20 grams of protein daily to 7 people for one year. Edible cottonseed could potentially supply half of the protein needs of 85 million people annually. Gossypol is a cardio- and hepatotoxic terpenoid found in the glands of cotton. Gossypol renders cottonseed unsafe for human/monogastric animal consumption. Therefore, a major portion of an abundant agricultural resource, rich in oil and protein, is utilized only as feed for ruminant animals. Gossypol and related terpenoids are derived from a precursor, (+)-δ-cadinene, that is present in the glands of the foliage, floral organs, and roots where they provide natural protection from pests. Conventional breeding has been unable to remove gossypol from the seed while maintaining it in the plant. Advances in molecular biology offer an alternative. Gossypol production in the seed has been disrupted by silencing a key gene, for δ-cadinene synthase. This is the same enzyme that is absent in the naturally occurring “glandless” mutant. RNAi, under the control of a seed-specific promoter, was used to silence the gene exclusively in the seed. Plants have been successfully generated that produce seeds with gossypol levels well below that considered safe by FDA (450 ppm) while maintaining normal levels of gossypol in the plant for defense against pests. No adverse effects on the fiber have been observed in the RNAi lines. The seed-specific elimination of gossypol unlocks a large amount of protein for improvement of human and animal nutrition.