Subtype-selective Agonist of Phytohormone Receptor and Molecular Probe for Target Identification by Phytotoxin Coronatine Derivatives

<p>The natural phytotoxin coronatine exhibits various biological activities as a mimic of jasmonoyl L-isoleucine (JA-Ile), which is one of the active forms of phytohormones that regulates many aspects of growth, development, and environmental responses in plants. In the jasmonic acid (JA) responses, JA-Ile induces the protein-protein interaction between an F-box protein (COI1) and a JAZ repressor, and their subsequent degradation by the ubiquitination/26S-proteasome pathway. Although we now have a much better understanding of the mechanism of JA signaling, many questions remain, partially due to the complicated combination of COI1-JAZ subtypes. In this research, we achieved the total synthesis of coronatine and their enantiomeric derivatives. From our original screening system for ligand of COI1-JAZ co-receptor in vitro, combined with the biochemical analyses in planta, we successfully discovered that one of the coronatine-derivatives is a potential ligand for specific JAZ subtype and COI1. This molecule is expected to be a powerful chemical biology tool to reveal the molecular basis of JA responses.</p><p>Coronatine is also known to cause stomatal reopening by affecting the guard cells to keep the infection route for bacterial pathogen. However, the target protein of coronatine involved in stomatal reopening has not been identified, and therefore, the molecular mechanism is still unclear. In the second topic, we newly designed and synthesized a coronatine-based photoaffinity probe to identify the stomatal reopening target. From the several biological assays in vitro and in planta, this probe kept stomatal reopening activity, whereas the binding affinity with COI1-JAZ complex significantly reduced. These results clearly indicated that we succeeded in uncoupling of the dual bioactivies of coronatine, and the probe would be a useful molecular probe for identification of unknown target protein involved in stomatal reopening caused by coronatine.</p>