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α-Tocopherol (vitamin E) is a lipid-soluble antioxidant synthesized only by photosynthetic organisms. α-Tocopherol is an essential component of mammalian diets, and intakes in excess of the U.S. recommended daily allowance are correlated with decreased incidence of a number of degenerative human diseases. Plant oils, the main dietary source of tocopherols, typically contain α-tocopherol as a minor component and high levels of its biosynthetic precursor, γ-tocopherol. A genomics-based approach was used to clone the final enzyme in α-tocopherol synthesis, γ-tocopherol methyltransferase. Overexpression of γ-tocopherol methyltransferase inArabidopsis seeds shifted oil compositions in favor of α-tocopherol. Similar increases in agricultural oil crops would increase vitamin E levels in the average U.S. diet.
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