The plant hormone jasmonate plays crucial roles in regulating plant responses to herbivorous insects and microbial pathogens and is an important regulator of plant growth and development1,2,3,4,5,6,7. Key mediators of jasmonate signalling include MYC transcription factors, which are repressed by jasmonate ZIM-domain (JAZ) transcriptional repressors in the resting state. In the presence of active jasmonate, JAZ proteins function as jasmonate co-receptors by forming a hormone-dependent complex with COI1, the F-box subunit of an SCF-type ubiquitin E3 ligase8,9,10,11. The hormone-dependent formation of the COI1–JAZ co-receptor complex leads to ubiquitination and proteasome-dependent degradation of JAZ repressors and release of MYC proteins from transcriptional repression3,10,12. The mechanism by which JAZ proteins repress MYC transcription factors and how JAZ proteins switch between the repressor function in the absence of hormone and the co-receptor function in the presence of hormone remain enigmatic. Here we show that Arabidopsis MYC3 undergoes pronounced conformational changes when bound to the conserved Jas motif of the JAZ9 repressor. The Jas motif, previously shown to bind to hormone as a partly unwound helix, forms a complete α-helix that displaces the amino (N)-terminal helix of MYC3 and becomes an integral part of the MYC N-terminal fold. In this position, the Jas helix competitively inhibits MYC3 interaction with the MED25 subunit of the transcriptional Mediator complex. Our structural and functional studies elucidate a dynamic molecular switch mechanism that governs the repression and activation of a major plant hormone pathway.
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This research is supported by the Gordon and Betty Moore Foundation (GBMF3037, to S.Y.H.), the China Scholarship Council (to F.Z.), Van Andel Research Institute (to H.E.X. and K.M.), the National Institutes of Health (R01 GM102545 to K.M. and R01AI060761 to S.Y.H.), and the Department of Energy (the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science Grant DE–FG02–91ER20021 (to S.Y.H.). We thank S. Grant for administrative support and staff members of the Life Science Collaborative Access Team of the Advanced Photon Source for assistance in data collection at the beam lines of sector 21, which is in part funded by the Michigan Economic Development Corporation and the Michigan Technology Tri-Corridor (grant 085P1000817). Use of the Advanced Photon Source was supported by the Office of Science of the US Department of Energy, under contract number DE-AC02-06CH11357. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We also thank G. Howe and K. Aung for reading the manuscript.
Extended data figures
All the structures are shown in cartoon representation. MYC3 N-terminal domain structure is colored in cyan for JID domain, green for TAD domain, red for the partial α1 helix and yellow for the rest of the protein. JasJAZ9 peptide is colored in pink. Although the α1’/α1 helices are well-resolved in the apo MYC3 structure, only partial α1 helix is shown since the rest of the α1 helix is disordered in the MYC3(5-242)–JasJAZ9 complex structure. The movie was made using the Chimera program with the superimposed apo MYC3(5-242) and JasJAZ9 bound MYC3(5-242) structures.
All the structures are shown in cartoon representation with COI1 colored in blue and JasJAZ9 peptide colored in pink. JA-Ile is shown as a space-filling model. The starting conformation of JasJAZ9 peptide is shown as an α-helix based on JasJAZ9- bound MYC3 complex structure. JasJAZ9 peptide undergoes conformational change at the N terminus upon binding to COI1 and JA-Ile. The movie was made using the Chimera program with the superimposed JasJAZ9-bound MYC3 (this study) and JasJAZ1-bound COI123 structures.