Molecular characterization of tocopherol biosynthesis genes from Olea europaea (L.) cv. Ayvalık

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 fruit collected at 15-day intervals between October and December 2014. We compared the expression levels of genes using quantitative RT-PCR and determined the tocopherol content using the high-performance liquid chromatography-fluorescence detection (HPLC-FLD) technique during fruit maturation in the Ayvalık cultivar. High OeHPT1, OeVTE3, OeVTE1, and OeGTMT expression was noted in young fruit. However, the OePDS1 mRNA did not exhibit significant expression changes during maturation. The α-tocopherol content varied between 26.78 and 21.05 mg/100 g and was highest at the early stages of fruit development. In addition, expression studies and tocopherol content revealed that tocopherol biosynthesis in olive is more active at the early stages of fruit maturation.