Overexpression of SlMPBQMT (VTE3) enhances α-tocopherol accumulation and reduces oxidative stress in tomato

Vitamin E (tocopherols) comprises a group of important lipid-soluble antioxidants that protect cellular membranes from oxidative damage in plants. Tocopherol biosynthesis occurs in plastids and involves several enzymes encoded by the VTE gene family. Among these genes, VTE3 encodes a 2-methyl-6-phytyl-1,4-benzoquinol methyltransferase that catalyzes a critical methylation step in the tocopherol biosynthetic pathway. However, the role of VTE3 in regulating α-tocopherol accumulation, oxidative stress responses, and the expression of tocopherol biosynthesis-related genes in tomato remains unclear. To investigate the function of VTE3, transgenic tomato plants overexpressing VTE3 were generated using Agrobacterium-mediated transformation. Nine independent overexpression lines were confirmed by quantitative real-time PCR analysis. High-performance liquid chromatography revealed increased α-tocopherol accumulation in fruits of transgenic tomato plants compared with non-transgenic plants. Among the tocopherol biosynthesis-related genes analyzed, GGDR showed the most pronounced transcriptional increase in the overexpression lines, whereas VTE1, VTE2, and VTE4 showed relatively modest or genotype-dependent changes. Interestingly, exogenous α-tocopherol treatment significantly induced GGDR expression, suggesting a potential association between α-tocopherol accumulation and GGDR regulation. Furthermore, reactive oxygen species accumulation in response to abiotic stress exposure was reduced in the transgenic lines, as indicated by nitro blue tetrazolium and 3,3′-diaminobenzidine staining, supporting an association between increased α-tocopherol accumulation and reduced ROS accumulation. The findings demonstrate that VTE3 overexpression enhances α-tocopherol accumulation, is associated with increased GGDR expression, and reduces ROS accumulation in tomato. In addition, the induction of GGDR expression following exogenous α-tocopherol treatment suggests a potential link between α-tocopherol accumulation and precursor supply during tocopherol biosynthesis. These results provide novel insights into the regulation of vitamin E biosynthesis and identify VTE3 as a promising target for metabolic engineering to improve vitamin E content and oxidative stress responses in tomato and other horticultural crops.