Ectopic expression of apple fruit homogentisate phytyltransferase gene (MdHPT1) increases tocopherol in transgenic tomato (Solanum lycopersicum cv. Micro-Tom) leaves and fruits

Homogentisate phytyltransferase (HPT) is an important enzyme in the biosynthesis of tocopherols (vitamin E). Herein, an HPT homolog (MdHPT1) was isolated from apple (Malus domestica Borkh. cv. Fuji) fruits, whose gene expression level gradually decreased during fruit ripening, reaching a background level in ripened apple fruits. The amounts of alpha- and gamma-tocopherols, two major tocopherols in plant organs, were 5- to 14-fold lower in the fruits than in the leaves and flowers of apple plants. Transgenic tomato plants (Solanum lycopersicum cv. Micro-Tom) overexpressing MdHPT1 were next constructed. Transgenic independent T-1 leaves contained similar to 1.8-to 3.6-fold and similar to 1.6-to 2.9-fold higher levels of alpha-tocopherol and gamma-tocopherol, respectively, than those in control plants. In addition, the levels of alpha-tocopherol and gamma-tocopherol in 35S:MdHPT1 T-1 fruits increased up to 1.7-fold and 3.1-fold, respectively, as compared to the control fruits, indicating that an increase in alpha-tocopherol in fruits (maximal 1.7-fold) was less evident than that in leaves (maximal 3.6-fold). This finding suggests that the apple MdHPT1 plays a role in tocopherol production in transgenic tomatoes. (C) 2010 Elsevier Ltd. All rights reserved.