Enhancement of Vitamin E Levels in Corn

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.

• alpha (α)-tocopherol
• corn
• gamma (γ)-tocopherol
• quantitative trait loci (QTL)
• transgenics
• vitamin E

Key teaching points:

• Vitamin E is the common name that describes eight naturally occurring compounds possessing α-tocopherol activity; all vitamin E compounds have antioxidant activity.

• There is natural variation for levels of vitamin E compounds in corn grain, with γ-tocopherol in highest abundance followed by α-tocopherol.

• Selecting for enhanced levels of α-tocopherol and γ-tocopherol with HPLC analysis in commercial corn breeding programs is too labor intensive and time consuming to be practical.

• Molecular marker mapping has identified chromosomal segments with desirable genes controlling levels of α- and γ-tocopherol. These markers are being used to indirectly select for higher levels of α- and γ-tocopherols in corn grain.

• Transgenic technology has been used in the model plant Arabidopsis to convert most γ-tocopherol to α-tocopherol, similar efforts have been initiated in corn.

Key teaching points:

• Vitamin E is the common name that describes eight naturally occurring compounds possessing α-tocopherol activity; all vitamin E compounds have antioxidant activity.

• There is natural variation for levels of vitamin E compounds in corn grain, with γ-tocopherol in highest abundance followed by α-tocopherol.

• Selecting for enhanced levels of α-tocopherol and γ-tocopherol with HPLC analysis in commercial corn breeding programs is too labor intensive and time consuming to be practical.

• Molecular marker mapping has identified chromosomal segments with desirable genes controlling levels of α- and γ-tocopherol. These markers are being used to indirectly select for higher levels of α- and γ-tocopherols in corn grain.

• Transgenic technology has been used in the model plant Arabidopsis to convert most γ-tocopherol to α-tocopherol, similar efforts have been initiated in corn.