Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2008
Publication Date: 11/29/2008
Citation: Liu, J., Stipanovic, R.D., Bell, A.A., Puckhaber, L.S., Magill, C.W. 2008. Stereospecific coupling of hemigossypol to (+)-gossypol in MOCO cotton is mediated by a dirigent protein. Phytochemistry. 69:3038-3042.
Interpretive Summary: Cottonseed is composed of approximately 22.5% of a high quality protein. However, cottonseed is underutilized as a food/feed source because of the presence of a toxic compound called gossypol. Gossypol occurs in the seed, foliage and roots of cotton where it imparts resistance against herbivorous insects and pathogens. Gossypol exists in two forms referred to as (+) or (-) forms. Toxicity to animals is mainly due to the (-)-form. The (+) and (-) forms appear to be equally toxic to insects and pathogens. Our goal is to produce cotton plants that make only (+)-gossypol and we expect the plants will retain the ability to fight off insects and pathogens and yet their seeds could be safely used as food/feed. We have identified and partially purified the agent responsible for controlling the ratio of (+) to (-) forms of gossypol. This discovery will assist our efforts to achieve our goal of creating cotton plants that only make (+)-gossypol by providing tools for cotton breeders to efficiently incorporate this trait into commercial cotton cultivars.
Technical Abstract: The terpenoid gossypol, a secondary metabolite found in the cotton plant, is synthesized by a high energy free radical dimerization of hemigossypol. Gossypol exists as an enantiomeric mixture because of restricted rotation around the central binaphthyl bond. The dimerization of hemigossypol is both regio- and stereospecific. The mechanism that controls this dimerization is poorly understood. In this paper we demonstrate that a dirigent protein controls this dimerization process. A partially purified protein preparation from cotton flower petals and exogenous laccase converted hemigossypol with a 30% enantiomeric excess into (+)-gossypol.