IntroductionAntioxidants scavenge reactive oxygen species to protect cells from their cytotoxic effects (Fryer, 1992). Cells produce reactive oxygen species as a by-product of several metabolic pathways and increase their production in response to biotic or abiotic stress. When accumulated in cells, reactive oxygen species can damage DNA, protein, and lipids (Gechev et al., 2003;Hurst et al., 2004). Thus, antioxidants, such as tocopherols, maintain the balance between production and scavenging of reactive oxygen species.Vitamin E is a group of compounds including tocopherols, metabolites with high antioxidant effects (Kamal-Eldin and Appelqvist, 1996). Tocopherols are mostly synthesized by oil plants and are known for their beneficial effects on human diseases such as coronary heart disease and cancer (Rimm et al., 1993;Yang et al., 2012). In plants, tocopherols are involved in plant responses to abiotic stress, cell membrane stability, signal transduction, and control of light stress in chloroplasts (Munné-Bosch and Alegre, 2002). In addition to their antioxidant effects, tocopherols have other functions, including prevention of lipid oxidation (Frankel, 1996), cell signaling, and gene regulation (Azzi et al., 2004;Rimbach et al., 2010).Five proteins, including methyltransferase and cyclase enzymes, participate in tocopherol biosynthesis (Lushchak and Semchuk, 2012). The PDS1 enzyme initiates biosynthesis via 4-4-hydroxyphenyl pyruvic acid (p-HPPA) and produces homogentisate (Norris, 1998). Then HPT1 synthesizes 2-methyl-6-phytyl-1,4benzoquinol (MPBQ) from homogentisate (Collakova, 2003). MPBQ is the precursor of all tocopherol forms. VTE3 and VTE1 synthesize γ-tocopherol from MPBQ (Porfirova et al., 2002). GTMT transfers a methyl group to γ-tocopherol and forms α-tocopherol (Koch et al., 2003).Genes involved in tocopherol biosynthesis were previously characterized in different model organisms (DellaPenna and Pogson, 2006;Quadrana et al., 2013), and recent studies revealed an association between tocopherol content and expression levels of genes Abstract: Vitamin E is a group of compounds that includes metabolites known as tocopherols, which have high antioxidant activities. Tocopherols are synthesized in plants, and their beneficial effects on human health have been reported for diseases such as coronary heart disease and cancer. Here we report the full-length transcripts encoding vitamin E biosynthetic enzymes from fruit mesocarp tissues using the rapid amplification of cDNA ends (RACE) method for the first time in olives. We characterized the structure of the genes 4-hydroxyphenylpyruvate dioxygenase (PDS1), homogentisate phytyltransferase 1 (HPT1), vitamin E defective 3 (VTE3), tocopherol cyclase (VTE1), and gamma tocopherol methyltransferase (GTMT), which are responsible for tocopherol biosynthesis in the olive cultivar Ayvalık. Although PDS1 is widespread in all organisms, HPT1, VTE3, VTE1, and GTMT are only present in photosynthetic organisms. We isolated total RNA from the dissected mesocarp tissues of fr...