Enhancement of Vitamin E Levels in Corn

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Abstract
Vitamin E is the common name that describes eight naturally occurring compounds possessing α-tocopherol activity. These eight vitamin E compounds are collectively termed tocols, and all have antioxidant activity. There is natural variation among different corn breeding lines for levels of tocols. The two predominant isomers present in corn grain are γ-tocopherol and α-tocopherol. α-tocopherol is considered more desirable for human and animal consumption because it has higher biological activity than γ-tocopherol. Most corn breeding lines naturally have much more γ-tocopherol than α-tocopherol. Therefore a breeding goal is to increase levels of α-tocopherol relative to γ-tocopherol. However, recent research suggests that γ-tocopherol and compounds metabolized from it have properties important to human health that are unique from properties of α-tocopherol. Therefore it may be desirable to not only increase levels of α-tocopherol in corn grain, but also levels of γ-tocopherol. Determination of levels of tocopherols in corn grain is very laborious, requires HPLC analysis and is too time consuming for use in routine commercial corn breeding programs. Therefore we are performing biotechnology enabled molecular marker mapping of chromosomal regions with genes that control levels and ratios of α- and γ-tocopherol. Breeders can use molecular markers we have identified to expediently select for desirable alleles of genes that will improve levels of α- and γ-tocopherol in corn grain, without having to perform laborious HPLC assays. Another biotechnology strategy we have initiated is genetic transformation of corn with the γ-tocopherol methyl transferase gene to enhance conversion of γ-tocopherol to α-tocopherol and thus increase levels of α-tocopherol. This transgenic strategy has been demonstrated in the model plant Arabidopsis, and we are now applying this approach to corn.