Submitted to: World Cotton Research Conference Proceedings
Publication Type: Review Article
Publication Acceptance Date: August 13, 2007
Publication Date: September 10, 2007
Citation: Liu, J., Bell, A.A., Stipanovic, R.D., Puckhaber, L.S. 2007. Increasing cottonseed utilization through breeding and genetic engineering to produce high levels of (+)-gossypol in seed. Proceedings of World Cotton Research Conference, September 10-14, 2007, Lubbock, Texas. 2007 CDROM. Technical Abstract: Cottonseed is composed of ~22.5% of high quality protein. The estimate of world cottonseed production for 2006 is over 42.5 million metric tons (National Agricultural Statistics Service, USDA, 2005), which translates to an estimated 9.56 million metric tons of protein available for use as a food/feed source. However, only a portion of cottonseed and thus its protein is actually utilized for food/feed. This under-utilization is due to the presence within most commercial cottonseed of a toxic compound called gossypol. Ruminants such as beef and dairy cattle, sheep and goats are capable of ingesting low levels of toxic gossypol without harmful effects, but non-ruminants such as humans and chickens are susceptible to harm. The toxic metabolite, gossypol, occurs in the seed, foliage, and roots of cotton where it provides protection against herbivorous insects and pathogens. Gossypol is biosynthesized by high-energy free radical coupling of two molecules of hemigossypol which yields two optically active enantiomers, (+)-gossypol and (-)-gossypol. In most commercial cottons (Gossypium hirsutum) grown in the U.S., the ratio of (+)- to (-)-gossypol is approximately 3:2. However, this ratio can be as high as 98:2 in some Moco cotton (G. hirsutum marie galante) accessions. Significantly, only (-)-gossypol is toxic to animals while toxicity toward insects and pathogens is independent of the (+)- to (-)-gossypol ratio. Therefore, if the ratio could be shifted predominately to (+)-gossypol in the seed, cottonseed could be used as a feed for non-ruminant animals. Advances in breeding cotton plants for high (+)-gossypol seed, and the protein that controls the biosynthesis of (+)- and (-)-gossypol are the subjects of this paper.