Cahoon Edgar B, Hall Sarah E, Ripp Kevin G, Ganzke Thaya S, Hitz William D, Coughlan Sean J
Crop Genetics Research and Development, Pioneer Hi-Bred, A DuPont Company, Experimental Station, Wilmington, Delaware 19880, USA.
Nat Biotechnol. 2003 Sep;21(9):1082-7. doi: 10.1038/nbt853. Epub 2003 Aug 3.
Tocotrienols are the primary form of vitamin E in seeds of most monocot plants, including cereals such as rice and wheat. As potent antioxidants, tocotrienols contribute to the nutritive value of cereal grains in human and livestock diets. cDNAs encoding homogentisic acid geranylgeranyl transferase (HGGT), which catalyzes the committed step of tocotrienol biosynthesis, were isolated from barley, wheat and rice seeds. Transgenic expression of the barley HGGT in Arabidopsis thaliana leaves resulted in accumulation of tocotrienols, which were absent from leaves of nontransformed plants, and a 10- to 15-fold increase in total vitamin E antioxidants (tocotrienols plus tocopherols). Overexpression of the barley HGGT in corn seeds resulted in an increase in tocotrienol and tocopherol content of as much as six-fold. These results provide insight into the genetic basis for tocotrienol biosynthesis in plants and demonstrate the ability to enhance the antioxidant content of crops by introduction of an enzyme that redirects metabolic flux.
生育三烯酚是大多数单子叶植物种子中维生素E的主要形式，包括水稻和小麦等谷物。作为强效抗氧化剂，生育三烯酚有助于谷物在人类和牲畜饮食中的营养价值。从大麦、小麦和水稻种子中分离出了编码尿黑酸香叶基香叶基转移酶（HGGT）的cDNA，该酶催化生育三烯酚生物合成的关键步骤。大麦HGGT在拟南芥叶片中的转基因表达导致了生育三烯酚的积累，而未转化植物的叶片中不存在生育三烯酚，并且总维生素E抗氧化剂（生育三烯酚加生育酚）增加了10至15倍。大麦HGGT在玉米种子中的过表达导致生育三烯酚和生育酚含量增加多达六倍。这些结果为植物中生育三烯酚生物合成的遗传基础提供了见解，并证明了通过引入一种重新引导代谢通量的酶来提高作物抗氧化剂含量的能力。
