Increased α-tocotrienol in GM Rice Seeds overexpressing Arabidopsis γ-tocopherol Methyltransferase

Vitamin E is an essential component of the human diet. It contributes in the functionality of the immune system and also reduces the risk of several degenerative diseases. Of the eight lipid soluble compounds consisting the vitamin, tocopherol and tocotrienol have the highest antioxidant activities. The enzyme γ-tocopherol methyltransferase (γ-TMT) catalyzes the last step in the production of vitamin E, the methylation of γ- and δ-isomers to α- and β-isomers.

Qiao-Quan Liu of Yangzhou University and colleagues over-expressed the Arabidopsis γ-TMT (AtTMT) in the nutritive tissue of Wuyujing rice seeds through Agrobacterium-mediated transformation. The team used high performance liquid chromatography analysis and found that the α-/γ-tocotrienol ratio of the wild type was only 0.7, much lower than that for tocopherol (~19.0). In the GM rice, most of the γ-isomers were converted to α-isomers, especially the γ- and δ-tocotrienol. This led to increased levels of α-tocotrienol in the GM seeds. The over-expression of AtTMT in the seeds also led to an increase in α-tocotrienol levels.

It was also shown that the ratio of α-/γ-tocopherol increased in the GM seeds, but there was no impact on α-tocopherol content. This may imply that γ-tocopherol is only available in miniscule amounts in the seeds of wild type rice. AtTMT over-expression had no effect on the absolute total content of both tocopherols and tocotrienols.

The results of this study is the first reported account that overexpression of a foreign γ-TMT affects the tocotrienol production in rice.

Read the abstract at http://www.springerlink.com/content/y0308448nx258854/.