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United States Department of Agriculture

Agricultural Research Service

Title: Increased (ALPHA)-tocopherol content in soybean seed overexpressing the Perilla frutescens (GAMMA)-tocopherol methyltransferase gene

Authors
item Tavva, Venkata - UK AGRONOMY
item Kim, Yul-Ho - NIC-KOREA
item Kagan, Isabelle
item Dinkins, Randy
item Kim, Kyung-Hwan -
item Collins, Glenn -

Submitted to: Plant Cell Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2006
Publication Date: August 15, 2006
Citation: Tavva, V.S., Kim, Y., Kagan, I., Dinkins, R.D., Kim, K., Collins, G.B. 2006. Increased (ALPHA)-tocopherol content in soybean seed overexpressing the Perilla frutescens (GAMMA)-tocopherol methyltransferase gene. Plant Cell Reports. 26:61-70.

Interpretive Summary: Tocopherols, which are the precursors to Vitamin E, are synthesized by photosynthetic organisms with antioxidant properties, play important roles 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 (alpha)-tocopherol is the most bioactive form of Vitamin E. This suggests that the final step of the (alpha)-tocopherol biosynthetic 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 the Perilla frutescens was overexpressed 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, synthesized by photosynthetic organisms with antioxidant properties, play important roles 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 (alpha)-tocopherol is the most bioactive component. This suggests that the final step of the (alpha)-tocopherol biosynthetic pathway catalyzed by (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 the Perilla frutescens was overexpressed using a seed-specific promoter. 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. In addition, the data obtained on lipid peroxidation indicates 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 (alpha)-tocopherol content of the soybean seed could have the potential to significantly increase the dietary intake of vitamin E.

Last Modified: 11/21/2014
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