Characterization of Arabidopsis SUMO conjugation as orchestrator of nuclear bodies and transcription

Small ubiquitin-like modifier (SUMO) is a conserved post-translational modification that regulates many biological processes in animal, yeast and plant cells. SUMO can be covalently attached to its target proteins at lysine residues present in short consensus peptide motifs. To date, hundreds of proteins have been identified as bona fide SUMO targets for mammals. In Arabidopsis, however, more studies are required to fully understand the extent of SUMO regulation in plant cells. In this study we focused on analyses and further study of SUMO proteome in Arabidopsis. In chapter 2 of this thesis we analyzed the cellular processes that are regulated by sumoylation as well as we reviewed current strategies to study sumoylation. In chapter 3 we characterized the interaction interface between SUMO peptide (SUMO1) and enzymes involved in sumoylation: SCE1 and SIZ1. We demonstrated that the SUMO1∙SCE1∙SIZ1 complex resides in nuclear bodies (NBs), along with the ubiquitin E3 ligase COP1, a master regulator of photomorphogenesis. In order to identify new SUMO interactors and SUMO substrate, we performed high-throughput yeast 2-hybrid assay using SUMO peptide paralogs as well as SUMO (de)conjugation enzymes as baits. We found that SUMO machinery interacts with many transcriptional regulators belonging to many transcription factors (TFs) families (chapter 4) and well as with some important proteins involved in plant immunity (chapter 5) in nuclear bodies. We further analyze the found interactions in chapters 4 and 5. In chapter 6 we summarized the current knowledge on sub-nuclear structures and the potential role of SUMO in their biology.