Crowell Elizabeth F, McGrath J Mitchell, Douches David S
Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824, USA.
Transgenic Res. 2008 Apr;17(2):205-17. doi: 10.1007/s11248-007-9091-1. Epub 2007 Apr 6.
Vitamin E (tocopherol) is a powerful antioxidant essential for human health and synthesized only by photosynthetic organisms. The effects of over-expression of tocopherol biosynthetic enzymes have been studied in leaves and seeds, but not in a non-photosynthetic, below-ground plant organ. Genetic and molecular approaches were used to determine if increased levels of tocopherols can be accumulated in potato (Solanum tuberosum L.) tubers through metabolic engineering. Two transgenes were constitutively over-expressed in potato: Arabidopsis thaliana p-hydroxyphenylpyruvate dioxygenase (At-HPPD) and A. thaliana homogentisate phytyltransferase (At-HPT). alpha-Tocopherol levels in the transgenic plants were determined by high-performance liquid chromatography. In potato tubers, over-expression of At-HPPD resulted in a maximum 266% increase in alpha-tocopherol, and over-expression of At-HPT yielded a 106% increase. However, tubers from transgenic plants still accumulated approximately 10- and 100-fold less alpha-tocopherol than leaves or seeds, respectively. The results indicate that physiological and regulatory constraints may be the most limiting factors for tocopherol accumulation in potato tubers. Studying regulation and induction of tocopherol biosynthesis should reveal approaches to more effectively engineer crops with enhanced tocopherol content.
维生素E（生育酚）是一种对人体健康至关重要的强大抗氧化剂，且仅由光合生物合成。生育酚生物合成酶过表达的影响已在叶片和种子中进行了研究，但尚未在非光合的地下植物器官中进行研究。采用遗传和分子方法来确定是否可以通过代谢工程在马铃薯（Solanum tuberosum L.）块茎中积累更高水平的生育酚。两个转基因在马铃薯中组成型过表达：拟南芥对羟基苯丙酮酸双加氧酶（At-HPPD）和拟南芥尿黑酸植基转移酶（At-HPT）。通过高效液相色谱法测定转基因植物中的α-生育酚水平。在马铃薯块茎中，At-HPPD的过表达导致α-生育酚最多增加266%，At-HPT的过表达使α-生育酚增加了106%。然而，转基因植物的块茎积累的α-生育酚分别仍比叶片或种子少约10倍和100倍。结果表明，生理和调控限制可能是马铃薯块茎中生育酚积累的最限制因素。研究生育酚生物合成的调控和诱导应能揭示更有效地培育生育酚含量提高的作物的方法。
