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United States Department of Agriculture

Agricultural Research Service

Title: Seed-Specific Expression of the Perilla Frutescens Gamma-Tocopherol Methyltransferase Gene in Soybean Results in Increase Alph-Tocopherol Content

Authors
item Tavva, Venkata - UK AGRONOMY
item Yul-Hoa, Kim - SUWON, KOREA
item KAGAN, ISABELLE
item DINKINS, RANDY

Submitted to: Biennial Conference on Molecular and Cellular Biology of the Soybean
Publication Type: Abstract Only
Publication Acceptance Date: June 20, 2006
Publication Date: August 5, 2006
Citation: Tavva, V.S., Yul-Hoa, K., Kagan, I., Dinkins, R.D. 2006. Seed-specific expression of the perilla frutescens gamma-tocopherol methyltransferase gene in soybean results in increase alph-tocopherol content. Biennial Conference on Molecular and Cellular Biology of the Soybean. Aug 5-8, 2006.

Interpretive Summary: Tocopherols, which are the precursors to Vitamin E, are synthesized by photosynthetic organisms. Vitamin E has been touted for its antioxidant properties, and plays an important role in human and animal nutrition. In crop plants, (gamma)-tocopherol, the biosynthetic precursor to (alpha)-tocopherol, is the predominant form found in the seed, whereas (alph)-tocopherol is the most bioactive form of Vitamin E. This suggests that the final step of the (alpha)-tocopherol biodyntheic pathway catalyzed by the enzyme, (gamma)-tocopherol methyltransferase, is limiting in soybean seed. Soybean oil occupies the major part of the edible oil consumed; therefore, manipulating the tocopherol biosynthetic pathway in soybean seed to convert tocopherols to most active (alpha)-tocopherol form could have significant health benefits. In order to increase the soybean seed (alpha)-tocopherol content, the (gamma)-tocopherol methyltransferase [(gamma)-TMT] gene isolated from Perilla frutescens was over expressed specifically in the seed. One transgenic plant was recovered and the progeny analyzed for two generations. The data obtained on the tocopherol content demonstrate that the seed specific expression of P. frutescens (gamma)-TMT gene resulted in a dramatic change in the tocopherol composition of the transgenic soybean seed compared to wild-type seed. On average a 10.4-fold increase in the (alpha)-tocopherol content and a 14.86-fold increase in the (beta)-tocopherol content were observed in the T2 seed. Given the relative contributions of the different tocopherols to Vitamin E activity, the activity in T2 seed was calculated to be 4.8-fold higher than in wild-type seed. The increase in the (alpha)-tocopherol content of the soybean seed could have the potential to significantly increase the dietary intake of Vitamin E.

Technical Abstract: Tocopherols, with antioxidant properties, are synthesized by photosynthetic organisms and play important roles in human and animal nutrition. In soybean, gamma-tocopherol, the biosynthetic precursor to alpha-tocopherol, is the predominant form found in the seed, whereas alpha-tocopherol is the most bioactive component. This suggests that the final step of the alpha-tocopherol biosynthetic pathway catalyzed by gamma-tocopherol methyltransferase (gamma-TMT) is limiting in soybean seed. Soybean oil is the major edible vegetable oil consumed, so manipulating the tocopherol biosynthetic pathway in soybean seed to convert tocopherols into the more active alpha-tocopherol form could have significant health benefits. In order to increase the soybean seed alpha-tocopherol content, the gamma-TMT gene isolated from Perilla frutescens was over expressed in soybean using a seed-specific promoter, vicilin. One transgenic plant was recovered and the progeny analyzed for two generations. The data obtained on the tocopherol content demonstrated that the seed specific expression of the P. frutescens gamma-TMT gene resulted in a dramatic change in the tocopherol composition of the transgenic soybean seed compared to wild-type seed. On average a 10.4-fold increase in the alpha-tocopherol content and a 14.9-fold increase in the beta-tocopherol content in the T2 seed. Given the relative contributions of the different tocopherol to Vitamin E activity, the activity in T2 seed was calculated to be 4.8-fold higher that in wild-type seed. In addition, the data obtained on lipid peroxidation indicate that alpha-tocopherol may have a role in preventing oxidative damage to the lipid components during seed storage and seed germination. The increase in the alph-tocopherol content in the soybean seed could have the potential to significantly increase the dietary intake of Vitamin E.

Last Modified: 9/29/2014
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