title: Increased α-tocotrienol content in seeds of transgenic rice overexpressing Arabidopsis γ-tocopherol methyltransferase.
abstract: Vitamin E comprises a group of eight lipid soluble antioxidant compounds that are an essential part of the human diet. The α-isomers of both tocopherol and tocotrienol are generally considered to have the highest antioxidant activities. γ-tocopherol methyltransferase (γ-TMT) catalyzes the final step in vitamin E biosynthesis, the methylation of γ- and δ-isomers to α- and β-isomers. In present study, the Arabidopsis                 γ-TMT (AtTMT) cDNA was overexpressed constitutively or in the endosperm of the elite japonica rice cultivar Wuyujing 3 (WY3) by Agrobacterium-mediated transformation. HPLC analysis showed that, in brown rice of the wild type or transgenic controls with empty vector, the α-/γ-tocotrienol ratio was only 0.7, much lower than that for tocopherol (~19.0). In transgenic rice overexpressing AtTMT driven by the constitutive Ubi promoter, most of the γ-isomers were converted to α-isomers, especially the γ- and δ-tocotrienol levels were dramatically decreased. As a result, the α-tocotrienol content was greatly increased in the transgenic seeds. Similarly, over-expression of AtTMT in the endosperm also resulted in an increase in the α-tocotrienol content. The results showed that the α-/γ-tocopherol ratio also increased in the transgenic seeds, but there was no significant effect on α-tocopherol level, which may reflect the fact that γ-tocopherol is present in very small amounts in wild type rice seeds. AtTMT overexpression had no effect on the absolute total content of either tocopherols or tocotrienols. Taken together, these results are the first demonstration that the overexpression of a foreign γ-TMT significantly shift the tocotrienol synthesis in rice, which is one of the world's most important food crops.
authors: Key Laboratory of Crop Genetics and Physiology of Jiangsu Province, Key Laboratory of Plant Functional Genomics of the Ministry of Education, College of Agriculture, Yangzhou University, Yangzhou, 225009, China.
authors: Gui-Yun
authors: GY
authors: Zhang
authors: Ru-Ru
authors: RR
authors: Liu
authors: Geng
authors: G
authors: Xu
authors: Peng
authors: P
authors: Zhang
authors: Yin
authors: Y
authors: Li
authors: Ke-Xuan
authors: KX
authors: Tang
authors: Guo-Hua
authors: GH
authors: Liang
authors: Qiao-Quan
authors: QQ
authors: Liu
mesh_terms: D000975:Antioxidants; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008780:Methyltransferases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D024505:Tocopherols / Q000302:isolation & purification / Q000378:metabolism; D024508:Tocotrienols; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
chemical_list: D000975:Antioxidants; D020033:Protein Isoforms; D024508:Tocotrienols; D014810:Vitamin E; C082032:tocotrienol, alpha; D008780:Methyltransferases; C047259:gamma-tocopherol methyltransferase; D024505:Tocopherols