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 development. Key mediators of jasmonate signalling include MYC transcriptio ...
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 development. 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 ligase. 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 repression. 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.
Organizational Affiliation:
Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824, USA.,Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503, USA.,DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.,Key Laboratory of Receptor Research, VARI-SIMM Center, Center for Structure and Function of Drug Targets, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.,College of Plant Protection, Nanjing Agricultural University, No. 1 Weigang, 210095, Nanjing, Jiangsu Province, China.,Department of Molecular Therapeutics, Translational Research Institute, The Scripps Research Institute, Scripps Florida, Jupiter, Florida 33458, USA.,College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang, China.,Department of Molecular Pharmacology and Biological Chemistry, Life Sciences Collaborative Access Team, Synchrotron Research Center, Northwestern University, Argonne, Illinois 60439, USA.,Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008, USA.,Howard Hughes Medical Institute, Michigan State University, East Lansing, Michigan 48824, USA.
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