Tavva Venkata S, Kim Yul-Ho, Kagan Isabelle A, Dinkins Randy D, Kim Kyung-Hwan, Collins Glenn B
Department of Plant and Soil Sciences, University of Kentucky, 1405 Veterans Road, Lexington, KY 40546-0312, USA.
Plant Cell Rep. 2007 Jan;26(1):61-70. doi: 10.1007/s00299-006-0218-2. Epub 2006 Aug 15.
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 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 overexpressed in soybean using a seed-specific promoter. One transgenic plant was recovered and the progeny was analyzed for two generations. Our results demonstrated that the seed-specific expression of the P. frutescens gamma-TMT gene resulted in a 10.4-fold increase in the alpha-tocopherol content and a 14.9-fold increase in the beta-tocopherol content in T2 seed. Given the relative contributions of 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 lipid components during seed storage and seed germination. The increase in the alpha-tocopherol content in the soybean seed could have a potential to significantly increase the dietary intake of vitamin E.
生育酚具有抗氧化特性，由光合生物合成，在人类和动物营养中发挥重要作用。在大豆中，γ-生育酚是α-生育酚的生物合成前体，是种子中发现的主要形式，而α-生育酚是最具生物活性的成分。这表明由γ-生育酚甲基转移酶（γ-TMT）催化的α-生育酚生物合成途径的最后一步在大豆种子中是受限的。大豆油是消费的主要食用植物油，因此操纵大豆种子中的生育酚生物合成途径以将生育酚转化为更具活性的α-生育酚形式可能对健康有显著益处。为了提高大豆种子中的α-生育酚含量，使用种子特异性启动子在大豆中过表达从紫苏中分离的γ-TMT基因。获得了一株转基因植物，并对其后代进行了两代分析。我们的结果表明，紫苏γ-TMT基因的种子特异性表达导致T2种子中α-生育酚含量增加10.4倍，β-生育酚含量增加14.9倍。考虑到不同生育酚对维生素E活性的相对贡献，计算得出T2种子中的活性比野生型种子高4.8倍。此外，关于脂质过氧化获得的数据表明，α-生育酚可能在防止种子储存和种子萌发期间脂质成分的氧化损伤中发挥作用。大豆种子中α-生育酚含量的增加可能有显著增加维生素E膳食摄入量的潜力。
