Protein Ubiquitination and Plant Response to Environmental Stress

Ubiquitination is a prevalent post-translation modification system that is involved in almost every aspects of eukaryotic biology. It involves the attachment of ubiquitin, a small, highly conserved protein to selected substrates. The outcome of ubiquitination varies depending on the nature of the modification and can include degradation, relocalization and activation of the substrate. The versatility of the ubiquitin molecule is due to the fact that it can be attached as a single molecule (monoubiquitination) or it can be used to build chains (polyubiquitination) of varying topology on an internal lysine residue of the substrate. The most notable function of ubiquitin is the targeting of substrate proteins to the multi-proteolytic 26S proteasome complex for degradation. The ubiquitin proteasome system (UPS) controls the abundance of numerous enzymes, structural and regulatory proteins ensuring proper cellular function. Plants, as sessile organisms, utilize the UPS to facilitate cellular changes required to respond to and tolerate adverse growth conditions. Environmental stresses such as water scarcity, increase temperature, nutrient derivation and pathogen infection can limit crop productivity by negatively impacting growth and development. Recent advances have broadened our understanding of UPS function, however major knowledge gaps remain including the identity of substrates and a clear understanding of how the system regulate protein abundance to facilitate stress responses. The goal of this research program is to gain an in-depth understanding of the regulatory role of the UPS in plant biology, particularly response to environmental stresses. We will identify proteins that are regulated by the UPS to facilitate responses required for defending against pathogen attack, increasing root iron uptake when availability is reduced, and enhancing tolerance of high temperature conditions. We will define the molecular mechanisms that regulate E3-substrate engagement to ensure that the appropriate response occurs to ameliorate damage during exposure to external stressors. We will also investigate the role of the UPS in regulating calcium-mediated stress signalling by studying the ubiquitin-dependent degradation of calcium activated protein kinases. This research will give insight into how the UPS can possibly be manipulated to provide an advantage to plants growing under unfavourable environmental conditions. Information obtained will aid in understanding UPS function in higher plants and better our understanding of similar processes in crops that are of commercial significance to the Canadian economy.