The plant hormone jasmonate (JA) plays an important role in regulating growth, development and defense against herbivores and microbial pathogens. A key step in JA signaling is perception of jasmonoyl-isoleucine (JA-Ile) by a co-receptor complex consisting of the F-box protein CORONATINE INSENSITIVE 1 (COI1) and Jasmonate Zim-Domain (JAZ) transcriptional repressors. COI1 is a component of an E3 ubiquitin ligase. The assembly of the COI1-JAZ receptor complex results in ubiquitination and proteasome-mediated degradation of JAZ repressors, which in the absence of JA-Ile bind to and repress transcription factors (e.g., MYC2) that control JA-dependent gene expression. Degradation of JAZ proteins results in transcriptional reprogramming that directs the cellular response to defense and JA-regulated developmental processes. Specific protein domains from each component of the JA receptor contribute to hormone perception. COI1 contains two conserved domains, an N-terminal F-box domain and a C-terminal leucine-rich repeat (LRR) domain, and it is the LRR domain that confers ligand and substrate specificity. All JAZ proteins share a conserved Jas motif near the C-terminus that is necessary for ligand-dependent binding to COI1. To gain an in-depth understanding of the COI1-JAZ interaction, I conducted a comprehensive structure-function analysis of the LRRCOI1 domain and the Jas motif of JAZ9. This analysis revealed amino acids that are critical for the ligand-dependent formation of the COI1-JAZ co-receptor, physical interaction between JAZ9 and a major JA-response transcription factor, MYC2, and nuclear targeting and repressor function of JAZ9 in Arabidopsis. The results from experiments described here contribute to the ongoing understanding of jasmonate perception and signal transduction and provide evidence for a novel transcription factor-dependent mechanism for nuclear import of transcriptional repressors in plants.
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