High Expression of Tocochromanol Biosynthesis Genes Increases the Vitamin E Level in a New Line of Giant Embryo Rice

'Shangshida No. 5' is a new variety of giant embryo rice derived from a single-point mutation of the giant embryo gene (ge) in 'Chao2-10' rice. This study quantified the levels of eight vitamin E homologues (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol) in brown rice, embryos, endosperm, and developing seeds of giant embryo and normal embryo rice using a normal phase high-performance liquid chromatographic method. Quantitative RT-PCR analysis was conducted to reveal the different expression patterns of the ge gene and tocochromanol biosynthesis genes in developing giant and normal embryo seeds. The total vitamin E content in 'Shangshida No. 5' brown rice was 52.54 mg alpha-tocopherol equivalent (alpha-TE)/kg,, of which alpha-tocopherol constituted 49.14 mg/kg which was approximately 2.2-fold greater than that in 'Chao2-10' brown rice. In giant embryo seeds, the expression level of the ge gene was higher than that in normal embryo seeds during early developmental stages. These results are the first to indicate that coup-regulated expression of the OsHPPD, OsHPT, and OsMPBQ MT2 genes might be the primary reason for the large accumulation of alpha-tocopherol in giant embryo rice seeds. The different transcription pattern of the tocochromanol biosynthesis genes in 'Shangshida No. 5' rice seeds compared with 'Chao2-10' rice seeds is attributable to the ge mutation and the different expression level of the ge gene in giant embryo seeds.