| The reversibly glycosylated polypeptides (RGP) are a family of four plant-specific proteins in Arabidopsis that have been implicated in cell wall biosynthesis. The main reasons for this hypothesis are that RGPs react with nucleotide sugars and are localized in the Golgi apparatus. Yet to date no direct evidence exists for the involvement of RGPs in the synthesis of cell wall components. To address this question, biochemical, genetic, and molecular biological approaches were taken. Arabidopsis RGPs were detected both in the Golgi apparatus and the cytoplasm. AtRGP1 and AtRGP2 are expressed in all tissues, and their respective proteins glycosylate in the presence of UDP-sugars, while AtRGP3 and AtRGP4 are only expressed in siliques, and their respective proteins do not glycosylate. AtRGP1 and AtRGP2 are functionally redundant and essential for plant development because an Arabidopsis homozygous T-DNA insertion mutant in both genes is lethal. The results obtained can be interpreted as follows: RGPs are involved in the transport of nucleotide sugars from the cytoplasm to the Golgi apparatus, where RGPs may deliver their cargo to the Golgi lumen. |
