Ubiquitination is a major eukaryotic protein modification process that attaches ubiquitin, a highly conserved small protein, to substrates. The ubiquitination process involves three consecutive enzymatic reactions that are catalyzed by ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2) and ubiquitin ligase (E3), respectively. In recent years, ubiquitination has emerged as a key regulatory mechanism of plant immunity against many pathogens. Several plant E3 ligases have been shown to act as either positive or negative regulators of host immunity and immunity-associated cell death. In contrast, roles of E2 enzymes in plant immunity, particularly those that direct non-classical lysine 63-specific ubiquitination, are virtually unknown. Opening a new perspective on plant immunity, the investigators have implicated in tomato defense against a bacterial pathogen an E2 ubiquitin-conjugating enzyme that directs lysine 63-specific ubiquitination. In this project the investigators will characterize key components of lysine 63-linked ubiquitination in plant immunity, which is of fundamental importance to the understanding of the regulation of plant immunity by the ubiquitination system. Additionally, this work will assist in efforts to unravel biological processes and proteins that are controlled by lysine 63-linked ubiquitination, knowledge of which is very limited at present. Integral to this project is training of post-doctoral, graduate and undergraduate students from minority groups that are underrepresented in science; incorporation of findings from this project to a dual-listed undergraduate-/graduate-level laboratory course taught at the PI's institution, where minority students currently make up over 30% of the student population; and partnering of the investigators with the Arkansas Cooperative Extension Service to distribute findings from this project to the general public and stakeholders.