Functional Characterization and Transcriptional Regulation of Olive Tocopherol Methyltransferase Responsible for the Vitamin E Content of Virgin Olive Oil.

The development of novel olive cultivars with enhanced vitamin E levels in their virgin olive oil is a major goal in olive breeding programs. This study reports the cloning and characterization of an olive cDNA, which encodes tocopherol methyltransferase (TMT) that catalyzes the last reaction of tocopherol biosynthesis. Sequence analysis and bacterial functional expression confirmed that the gene encodes an active TMT enzyme. Expression profiling across different olive tissues and cultivars revealed a cultivar-dependent spatial and temporal regulation of TMT transcripts. When combined with tocopherol profiling, the data suggest that OeTMT is implicated in the biosynthesis of the α-tocopherol present in olive mesocarp and, consequently, in the olive oil. Additionally, the α-tocopherol biosynthesis in the olive mesocarp appears to be transcriptionally regulated in response to environmental factors, including water status, temperature, light, and wounding, indicating that OeTMT could play a role in the response to abiotic stress.