Expression And Function Analyses Of Rice OsVTC1 Genes

Vitamin C (Vc), also named ascorbic acid (AsA), plays an important role in animals and plants. Human beings and some animals can not synthez AsA and have to acquire it from food. Therefore, plant AsA is the important source for human supplement. Though previous studies showed that L-galactose pathway is the main pathway of Arabidopsis, the expression characterization and function of L-galactose pathway-related key enzyme homologue genes in rice (Oryza sativa) are unclear.GDP-D-Mannose pyrophosphorylase (GME) is one of the key enzymes of Arabidopsis L-galactose pathway. The GME point mutant vtcl-1 has 25-30% AsA content of wild type.3 VTC1 homologous genes of Arabidopsis AtVTCl in rice are named as OsVTC 1-1/3/8. Consequently, we studied the expression of these genes and function in AsA biosynthesis. Our main results are showed as the followings.1. We have cloned three AtVTCl homologous genes from rice and named OsVTC 1-1, OsVTC 1-3, OsVTC1-8. The sequence alignment of OsVTC 1-1 and OsVTC1-8 reaches to 90% identities.2. We have got three purified recombination proteins from bacterial expression system, and found all of the three recombination proteins have GMP enzyme activities.3. Using Real-time PCR technology, we checked the expressions and ASA content of the 3 genes in wild type rice (Nipponbare), when exposed to different light and dark treatments.4.3 OsVTC 1 overexpression vectors were transformed into Arabidopsis mutant vtcl respectively. AsA contents in OsVTC1-1 and OsVTC 1-3 transgenic lines, but not in OsVTC1L-8 transgenic plants, were significantly increased,5. Using RNAi lines RNAi-OsVTC1-1 and 8 that knocked down simultaneously 2 genes, because of the high alignment, we found that AsA content decreased while RNAi-OsVTC1-3 had no effects on ASA contents.Conclusions:The data available from our research suggest that OsVTC 1-1 is the main contributor for GMP that might be involved in rice AsA synthesis.