Generation of transgenic tobacco plants with enhanced tocotrienol levels through the ectopic expression of rice homogentisate geranylgeranyl transferase

Abstract

Tocotrienols with three double bonds in the hydrocarbon tail are the major form of vitamin E in the seeds of most monocots and certain dicots. They have recently been attracting increasing attention for their various biological properties for human health. Homogentisate geranylgeranyl transferase (HGGT) catalyzes the committed step of tocotrienol biosynthesis. HGGT, except for enzyme from barley, has been not analyzed in detail, although cDNAs encoding HGGT have been isolated from barley, wheat, and rice. Since tocotrienol levels are higher in rice than in barley, rice HGGT (OsHGGT) may have superior enzymatic characteristics to those of barley HGGT. In the present study, we generated transgenic tobacco plants introducing OsHGGT cDNA into a nuclear genome and measured their tocopherol and tocotrienol levels. We demonstrated that the ectopic expression of OsHGGT enhanced tocotrienol levels without decreasing tocopherol levels in tobacco plants. The results of the present study may lead to a better understanding of the manipulation of vitamin E biosynthesis in leafy vegetables.