Abstract
Tocotrienols are the primary form of vitamin E in seeds of most monocot plants, including cereals such as rice and wheat. As potent antioxidants, tocotrienols contribute to the nutritive value of cereal grains in human and livestock diets. cDNAs encoding homogentisic acid geranylgeranyl transferase (HGGT), which catalyzes the committed step of tocotrienol biosynthesis, were isolated from barley, wheat and rice seeds. Transgenic expression of the barley HGGT in Arabidopsis thaliana leaves resulted in accumulation of tocotrienols, which were absent from leaves of nontransformed plants, and a 10- to 15-fold increase in total vitamin E antioxidants (tocotrienols plus tocopherols). Overexpression of the barley HGGT in corn seeds resulted in an increase in tocotrienol and tocopherol content of as much as six-fold. These results provide insight into the genetic basis for tocotrienol biosynthesis in plants and demonstrate the ability to enhance the antioxidant content of crops by introduction of an enzyme that redirects metabolic flux.
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Acknowledgements
We thank Jerry Ranch for conducting the corn transformation experiments. We also thank Alfred Ciuffetelli for assistance with corn seed analyses and Trissa Miller and Rebecca Cahoon for critical reading of the manuscript.
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Patent applications have been filed on the sequences and utility of the cDNAs described in the manuscript.
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Cahoon, E., Hall, S., Ripp, K. et al. Metabolic redesign of vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content. Nat Biotechnol 21, 1082–1087 (2003). https://doi.org/10.1038/nbt853
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DOI: https://doi.org/10.1038/nbt853
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