| Popis: |
Plants, as primary produces of energy and the main source of food for many organisms, are both ecologically and economically important to sustaining life. Understanding the molecular mechanisms by which plants respond to stress is key to optimizing food production and maintaining biodiversity in an increasingly uniform global ecosystem. Arabidopsis thaliana is the major model plant species in which primary research provides insights into the workings of more important plant species. The research presented here advances our understanding of the role of SUMOylation and deSUMOylation in plants. The discovery of a previously undescribed group of SUMO proteases in plants, called deSUMOylating Isopeptidases (DeSis) has provided evidence for the first time of SUMOylation cycles outside the nucleus. Using proteomic comparisons from animal species, this group of SUMO proteases has been classified into 3 distinct sub-classes; DeSi1, DeSi2 and the plant specific DeSi3. Characterisation of the SUMO isopeptidase activity was achieved through biochemical assays in which SUMO1 conjugation chains were reduced in the presence of the DeSi proteins. Furthermore, investigation into the role of the DeSi3 protein At1g47740 (DeSi3a), has revealed key regulation of the immune response pathway. DeSi3a knockout plants were more resistant to pathogen attack, showed a higher response to the detection of pathogenic elicitor molecules and appeared to be primed for immune response. Together this provided evidence that DeSi3a is a major negative regulator of plant immunity. In addition to this, investigation into potential DeSi3a target substrates has revealed that the activation of the key receptor for the perception of bacterial pathogens, FLS2, is SUMOylation dependent. Further evidence suggests that the fungal pathogen receptor, CERK1, may also be regulated by SUMO. This thesis provides evidence that the regulation of pathogen perception is SUMOylation dependent and that DeSi3a is a key negative regulator of defence. |
