Regulation of jasmonate biosynthesis by post-translational regulation of OPR3

The induction of plant defense responses against insect herbivores is mediated by jasmonates which start to accumulate within minutes after insect attack or wounding. How the rapid formation of these phytohormones is initiated, is an important open question in the defense signaling field. Rapid accumulation of jasmonates cannot be explained by changes in gene expression, but calls for post-translational mechanisms of regulation. According to our working hypothesis, post-translational regulation operates at the level of 12-oxophytodienoate reductase (OPR3), a central enzyme of jasmonate biosynthesis. We suggest that OPR3 activity depends on its oligomeric state which is controlled by reversible phosphorylation. The proposed research aims to substantiate this hypothesis by analyzing the oligomeric state of OPR3 in planta including its dynamic changes in response to environmental and developmental cues. OPR3 phosphorylation site(s) will be identified and wound-induced changes in phosphorylation quantified. We further aim to identify and characterize the protein kinase(s) responsible for OPR3 phosphorylation and determine it’s(their) role in defense signaling. This work will contribute substantially to a better understanding of jasmonate biosynthesis, plant defense signaling, structure activity relationships in OPR3, and the relevance of reversible protein phosphorylation in plants, particularly with respect to the regulation of defense responses.