UC Riverside

Plant leucine aminopeptidase A (LAP-A) modulates late wound responses and insectdefense. LAP-A is an aminopeptidase and chaperone in the chloroplast stroma. Based on the ability of LAP-A to modulate transcripts in the wound-response pathway, we postulated that LAP-A sends a retrograde signal(s) to the nucleus to regulate nuclear gene expression in response to wounding and MeJA treatments. We use wild-type, LapA-silenced and LapA-overexpressing plants to explore the global impact of LAP-A deficiency or ectopic expression on the tomato metabolome. This dissertation has revealed that LAP-A has multiple impacts on tomato metabolites by altering the levels of amino acids and secondary metabolites involved in plant defense. Given the link to sulfur metabolism and LAP-A’s ability to hydrolyze glutathione’s catabolic product Cys- Gly, the role of LAP-A in GSH metabolism using targeted metabolomics and the three genotypes was assessed. These wound-time course experiments were designed to simultaneously measure H2O2 levels. LAP-A did not regulate the levels of glutathione (GSH), the redox status of GSH, nor the levels of Cys-Gly, Cys or g-Glu-Cys. In the absence of LAP-A, H2O2 levels are elevated indicating that LAP-A is important for the control of ROS. H2O2 is a known retrograde signal used in defense. To elucidate LAPA’s possible mechanism(s) of action, the proteins that bind to LAP-A, but not to the highly related LAP-N, were identified. The 86 LAP-A-interacting proteins that reside in the chloroplast suggests that LAP-A may exert its effects via the major chloroplast redox hub associated with 2-Cys-peroxiredoxin. LAP-A binds to NADPH thioredoxin reductase- C (NTRC1), which provides the reducing power to 2-Cys-peroxiredoxin for clearing H2O2 from the chloroplast; a model is presented. Additional LAP-A-interacting proteins suggest a role for LAP-A in modulating the activity of the stromal Clp protease. Finally, this dissertation reports the first tomato stromal proteome. The 1254 stromal proteins identified were manually annotated. This is the first evidence for the chloroplast location of 550 tomato proteins. This study is foundational for current initiatives to understand the LAP-A- and MeJA-dependent changes in the tomato stromal proteome, which should provide additional insights into the global impacts of LAP-A during plant stress responses.