O-GlcNAc protein modification in plants

The modification of nucleocytoplasmic proteins with single O-GlcNAc moieties is a common post-translational modification. In animals, this modification is highly dynamic, and two enzymes, an O-GlcNAc-transferase, OGT, and the glycosyl hydrolase OGA are responsible for cycling of O-GlcNAc and thus mediating its regulatory role in signaling pathways. Global identification studies of O-GlcNAcylated proteins in mammalian cells have shown that a number of cellular processes such as gene expression, protein degradation and localization or cell cycle regulation involve O-GlcNAcylation, often integrating the response to nutrients and stress. Furthermore, there is strong evidence for interaction and competition of O-GlcNAcylation and phosphorylation in cellular signaling. While O-GlcNAcylation is intensily studied in animal systems, very little is known about this modification in plants. Plants have two partly redundant and functionally essential OGTs, as a double knockout of both enzymes is embryo-lethal. However, the functional homolog of OGA, the enzyme necessary for cleaving off the O-GlcNAc residue, has not been identified as yet. Hence, it is possible that fundamental functional differences in O- GlcNAcylation exist between animals and plants. So far, only few O-GlcNAcylated plant proteins have been identified, despite the importance of a functional OGT. The lack of known targets clearly hampers progress in studying the role of O-GlcNAcylation in plants. Given the importance of O-GlcNAcylation in animal cellular processes, it is fundamental to determine if this essential modification, that has been widely overlooked so far, has similar roles in plants. The experiments suggested in this proposal will provide further insights in the role of O-GlcNAcylation in plants. Different approaches such as a proteomic study, biochemical and genetic studies will be applied to identify pathways as well as target proteins that are affected by this post-translational modification. The combination of these methods will generate on the one hand a clearer picture of the role of protein O-GlcNAcylation in plants, differences and common mechanisms between plants and animals, and on the other hand reveal individual target proteins that can then be used as starting points to study the functional role of this modification in more biochemical and cell biological detail.