In eukaryotes, the ubiquitin (Ub) system has emerged at the center of many signaling mechanisms through their targeting of specific key proteins for ubiquitination and degradation by the 26S proteasome. The specificity of ubiquitination is conferred by Ub E3 ligase complexes, which serves as the substrate receptor and recruits E2 enzymes that catalyze transfer of Ub to a substrate lysine. Typically, E3s recognize substrates that are modified, often by phosphorylation (for more details, read Zheng & Shabek and Shabek & Zheng and Shabek & Ciechanover). Remarkably, plants evolved the Ub system to control numerous growth and developmental processes including senescence, embryogenesis, defense, hormone signaling, and environmental responses. Plants genome predicts more than 1,400 potential Ub ligases, almost twice higher number that most of them are without obvious counterparts in other eukaryotes. 
Despite the significant advances made in understanding the cellular mechanisms that underlie signal-dependent substrate recognition by the Ub system in plants, this field is largely unexplored. This notion is especially significant given the number of uncharacterized E3 ligases, target substrates, and countless signals that are yet to be unveiled. Our research aims to reveal and dissect how E3 ligases regulate cellular response to a variety of stimuli, and what the roles are of other components of the Ub system, including deubiquitinating enzymes, and Ub-like proteins in plants.