An expression analysis of the ascorbate biosynthesis enzyme VTC2.

The vtc2 mutant of Arabidopsis thaliana is vitamin C deficient and is defective in the ascorbate biosynthesis enzyme GDP-L-Galactose phosphorylase/L -Galactose guanylyltransferase. The connection between the VTC2 gene and this enzyme has only recently been established, and little is known about the molecular characteristics of the VTC2 gene. In this paper, the expression of the VTC2 gene was characterized on both the RNA and the protein level. The VTC2 gene was expressed in all developmental stages, and the mRNA was expressed at a higher level in green tissues than in the root. VTC2 mRNA expression was induced strongly by exposing dark-grown seedlings to light, to levels higher than found in light-grown seedlings. A VTC2:GUS fusion protein was detected only in green tissues. Unexpectedly, a VTC2:YFP fusion protein was found not only in the cytosol, but also in the nucleus, which suggests that GDP-L-Galactose phosphorylase/L: -Galactose guanylyltransferase might be a dual-function protein, which has both enzymatic and regulatory function.