Metabolic Engineering for Tocotrienol Accumulation in Perilla [Perilla frutescens (L.) Britton]

Abstract

Tocotrienols are the major form of Vitamin E in the seed of most monocot plants. They have been reported to exert a protective effect against cancer, diabetes and cardiovascular and neurological diseases. And it has been known that homogentisate geranylgeranyl transferase (HGGT) is a key enzyme for tocotrienol biosynthesis. Perilla (Perilla frutescens L. Britton) which has been cultivated as a fresh leafy vegetable as well as an oil crop in Asian countries, produces tocopherols, while tocotrienols do not accumulate in leaf tissues. To develop a transgenic perilla plant producing tocotrienol in leaf, the OsHGGT gene cloned from rice was introduced to a wild type perilla through Agrobacterium-mediated transformation. The T-DNA integration in plants was verified by PCR and the results of northern hybridization analysis showed there is the constitutive expression of OsHGGT gene in transgenic perilla. Also, alpha-tocotrienol identified by GC-Mass spectrometry was accumulated in leaves of transgenic Perilla, whereas the content of tocopherols was not reduced. alpha-Tocopherol was the predominant tocochromanol in both transformants and wild type plant. The average content of a-tocotrienol was 4.7 mu g/g DW (ranges from 2.5 to 8.6 mu g/g DW) in leaf tissues of transgenic plants. These results indicate that introducing the OsHGGT gene was useful for the accumulation of tocotrienols in leaf of perilla. The transgenic perillia with enhanced tocotrienol may provide a significant nutritional benefit to human health.