Transfer and Targeted Overexpression of γ-Tocopherol Methyltransferase (γ-TMT) Gene Using Seed-Specific Promoter Improves Tocopherol Composition in Indian Soybean Cultivars

Soybean oil contains high levels of tocopherols which are an important source of vitamin E in human diet. The conversion of gamma- to alpha-tocopherol catalyzed by gamma-tocopherol methyltransferase (gamma-TMT) is found to be the rate limiting factor in soybean which influences the tocopherol composition. Using Agrobacterium-mediated transformation, we overexpressed the gamma-TMT gene of Perilla frutescens under the control of the seed-specific promoter vicillin in cultivar Pusa 16. Transgene integration and expression was confirmed in five independently transformed GUS positive soybean plants by polymerase chain reaction (PCR), Southern hybridization, and reverse transcriptase-PCR (RT-PCR). High-performance liquid chromatography (HPLC) analysis showed that overexpression of Pf-gamma-TMT resulted in efficient conversion of gamma-tocopherol to alpha-tocopherol and concomitant increase in seed alpha-tocopherol content in RT-PCR positive plants. The protocol was successfully applied to three more cultivars PK 416, Gujarat soybean 1, and VL soya 1 inwhich seeds of transformed plants showed elevated level of alpha-tocopherol than wild-type seeds.