UC Riverside

Historically, peptidases have been considered as housekeeping proteins involved in protein degradation and amino acid turnover. However, recent work has highlighted the fact that peptidases, including aminopeptidases, have critical regulatory roles in the cell including modulation of growth, development and stress responses. Recently, plant leucine aminopeptidases (LAPs) have been recognized for their roles in modulation of late wound-responses and insect defense. While no known mechanism of action has been identified, LAPs were presumed to act through their aminopeptidase function to affect the stability, activity, or localization of a peptide and protein involved in defense. In my dissertation studies, I have identified two new molecular functions for plant LAPs as molecular chaperones and Cys-Gly dipeptidases. In addition, microarray analyses has demonstrated the tomato LAP-A regulates early and late wound responses both positively and negatively. In particular, microarray analyses identified two new sets of genes modulated by LAP-A: late wound dehydrins and Pathogenesis-Related 1. This study also provides evidence LAP-A may act though the negative regulator salicylic acid or the positive regulator hydrogen peroxide to modulate wound signaling. The role of LAP-A in glutathione metabolism is also discussed. Together this study has provided evidence that LAP-A's role in wound signaling and insect defense is more complex than initially anticipated and may be the result of LAP-A utilizing multiple functions (aminopeptidase, chaperone and/or Cys-Gly dipeptidase activities) in different environments and in response to different stresses.