A chemical inhibitor of jasmonate signaling targets JAR1 in Arabidopsis thaliana.

Jasmonates are lipid-derived plant hormones that regulate plant defenses and numerous developmental processes. Although the biosynthesis and molecular function of the most active form of the hormone, (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile), have been unraveled, it remains poorly understood how the diversity of bioactive jasmonates regulates such a multitude of plant responses. Bioactive analogs have been used as chemical tools to interrogate the diverse and dynamic processes of jasmonate action. By contrast, small molecules impairing jasmonate functions are currently unknown. Here, we report on jarin-1 as what is to our knowledge the first small-molecule inhibitor of jasmonate responses that was identified in a chemical screen using Arabidopsis thaliana. Jarin-1 impairs the activity of JA-Ile synthetase, thereby preventing the synthesis of the active hormone, JA-Ile, whereas closely related enzymes are not affected. Thus, jarin-1 may serve as a useful chemical tool in search for missing regulatory components and further dissection of the complex jasmonate signaling networks.