Development of subtype selective agonist for phytohormone receptor

<p> 　　Phytohormone (+)-7-iso-Jasmonoyl-L-isoleucine (JA-Ile) causes various physiological activities in planta, such as immune response, growth inhibition and enhancing of biosynthesis of secondary metabolites. In the jamonoic acid (JA) responses, JA-Ile induces Protein-Protein interaction (PPI) between F-box protein (COI1) and JAZ repressor. As previously reported, COI1 and 12 subtypes of JAZ proteins are coded in Arabidopsis thaliana. However, biological roles of each JAZ subtype have been remained unclear due to the high redundancy of JAZ genes, and subtype selective agonist for COI1/JAZ co-receptor would be a potential tool to reveal JA signaling pathway.</p><p> 　　In this research, we developed novel in vitro co-immunoprecipitation (Co-IP) assay system for screening of COI1/JAZ agonists by using epitope-conjugated JAZ degron peptides and GST-tagged COI1 protein. We initially assessed our original COR (a phytotoxin, which is a structural mimic of JA-Ile) derivatives, and we succeeded in obtaining the candidate of JAZ subtype selective agonist from this focused library. Moreover, we newly designed more selective agonist by in silico docking study based on crystal structure of COI1-COR-JAZ1, and one of the compounds would be a more selective ligand for COI1/JAZ. </p><p> 　　We finally evaluated these compounds in vivo using Arabidopsis thaliana as a model plant. In the results, one of our candidates caused accumulation of anthocyanin in a leaf, in spite of no or weak growth inhibition. These results clearly indicated that our newly designed COR-derivatives would distinguish JA response even in vivo.</p>