Accumulation of vitamin E in potato (Solanum tuberosum) tubers

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). α-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 α-tocopherol, and over-expression of At-HPT yielded a 106% increase. However, tubers from transgenic plants still accumulated approximately 10- and 100-fold less α-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.