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Title: METABOLIC REDESIGN OF VITAMIN E BIOSYNTHESIS IN PLANTS FOR TOCOTRIENOL PRODUCTION AND INCREASED ANTIOXIDANT CONTENT

Author
item Cahoon, Edgar
item HALL, SARAH - DUPONT CROP GENETICS
item RIPP, KEVIN - DUPONT CROP GENETICS
item GANZKE, THAYA - DUPONT CROP GENETICS
item HITZ, WILLIAM - DUPONT CROP GENETICS
item COUGHLAN, SEAN - DUPONT CROP GENETICS

Submitted to: Nature Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2003
Publication Date: 8/3/2003
Citation: Cahoon, Edgar B., Hall, Sarah E., Ripp, Kevin G., Ganzke, Thaya S., Hitz, William D., Coughlan, Sean J. Metabolic redesign of vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content. Nature Biotechnology. 2003. v. 21(9). p. 1082-1087.

Interpretive Summary: Tocotrienols are the principal form of Vitamin E in cereal grains including rice and wheat. These compounds are potent antioxidants and contribute to the nutritive value of cereal grains in the human diet and in animal feeds. In this study, genes were isolated from barley, wheat, and rice for an essential enzyme in the biosynthesis of tocotrienols. Transgenic expression of this enzyme was shown to confer tocotrienol biosynthetic ability to leaves and seeds of plants that do not normally produce this form of Vitamin E. Large increases in Vitamin E content were also shown to accompany the transgenic expression of this enzyme in plants. The findings of this study will be useful for molecular biologists and geneticists attempting to enhance the Vitamin E content of horticultural and agronomic crop plants. This research will ultimately result in increased nutritive value of foods for consumers and animal feeds for U.S. farmers and may also lead to increased productivity of crop plants.

Technical Abstract: Tocopherols and tocotrienols compose the Vitamin E family of antioxidants in plants and are important nutrient components in human and animal diets. While tocopherols are found in nearly all plant tissues, the occurrence of tocotrienols is limited primarily to the seeds of monocots, including cereal grains such as rice and wheat, where they are typically the major form of Vitamin E. The initial step in tocopherol biosynthesis is the condensation of homogentisic acid (HGA) and phytyl diphosphate, which is catalyzed by HGA phytyltransferase (HPT). Tocotrienols, in contrast, derive from the condensation of HGA and geranylgeranyl diphosphate via the activity of the previously uncharacterized HGA geranylgeranyl transferase (HGGT). cDNAs for a divergent HPT class were isolated from developing barley, wheat, and rice seeds. Consistent with the activity of an HGGT enzyme, transgenic expression of the barley cDNA in Arabidopsis leaves was accompanied by the accumulation of tocotrienols, which were absent from leaves of non-transformed plants. Expression of the barley cDNA in Arabidopsis leaves also resulted in a 10- to 15-fold increase in total Vitamin E antioxidants, principally in the form of tocotrienols. Similarly, transgenic expression of the barley cDNA in corn seeds was accompanied by a 25- to 40-fold increase in the tocotrienol content and a four- to six-fold increase in Vitamin E antioxidants. These results demonstrate the ability to engineer Vitamin E biosynthesis for the production and enhanced accumulation of nutritionally important antioxidants by introduction of a single enzyme that redirects metabolic flux.