Vitamin E biosynthesis in tubers of potato (Solanum tuberosum)

Vitamin E (tocopherol) is a powerful antioxidant essential for human health and synthesized only by photosynthetic organisms. The roles of tocopherol biosynthetic enzymes in regulating pathway flux have been established in leaves and seeds, but not in a non-photosynthetic, below-ground organ. Genetic and molecular approaches were used to determine if increased levels of tocopherols can be accumulated in potato (Solanum tuberosum) tubers through metabolic engineering. Two transgenes were constitutively overexpressed 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. Overexpression of At-HPPD resulted in a maximum 266% increase in a-tocopherol, and overexpression of At-HPT yielded a 106% increase. The results indicate that the tocopherol biosynthetic pathway in tubers is highly regulated compared to leaves and seeds, and physiological constraints may prevent effective engineering of enhanced tocopherol levels in potato.