Assembly of JAZ–JAZ and JAZ–NINJA complexes in jasmonate signaling

Jasmonates(JAs)are plant hormones with crucial roles in development and stress resilience.They activate MYC transcription factors by mediating the proteolysis of MYC inhibitors called JAZ proteins.In the absence of JA,JAZ proteins bind and inhibit MYC through the assembly of MYC–JAZ–Novel Interactor of JAZ(NINJA)–TPL repressor complexes.However,JAZ and NINJA are predicted to be largely intrinsically unstructured,which has precluded their experimental structure determination.Through a combination of biochemical,mutational,and biophysical analyses and AlphaFold-derived ColabFold modeling,we characterized JAZ–JAZ and JAZ–NINJA interactions and generated models with detailed,high-confidence domain interfaces.We demonstrate that JAZ,NINJA,and MYC interface domains are dynamic in isolation and become stabilized in a stepwise order upon complex assembly.By contrast,most JAZ and NINJA regions outside of the interfaces remain highly dynamic and cannot be modeled in a single conformation.Our data indicate that the small JAZ Zinc finger expressed in Inflorescence Meristem(ZIM)motif mediates JAZ–JAZ and JAZ–NINJA interactions through separate surfaces,and our data further suggest that NINJA modulates JAZ dimerization.This study advances our understanding of JA signaling by providing insights into the dynamics,interactions,and structure of the JAZ–NINJA core of the JA repressor complex.

JASMONATE-ZIM DOMAIN proteins engage Polycomb chromatin modifiers to modulate Jasmonate signaling in Arabidopsis

Jasmonate(JA)regulates various aspects of plant growth and development and stress responses,with prominent roles in male reproductive development and defenses against herbivores and necrotrophic pathogens.JASMONATE-ZIM DOMAIN(JAZ)proteins are key regulators in the JA signaling pathway and function to repress the expression of JA-responsive genes.Here,we show that JAZ proteins directly interact with several chromatin-associated Polycomb proteins to mediate repressive chromatin modifications at JA-responsive genes and,thus,their transcriptional repression in Arabidopsis.Genetic analyses revealed that the developmental defects,including anther and pollen abnormalities,resulting from loss or block of JA signaling were partially rescued by loss of Polycomb protein-mediated chromatin silencing(Polycomb repression).We further found that JAZ-mediated transcriptional repression during anther and pollen development requires Polycomb proteins at four key Regulatory loci.Analysis of genome-wide occupancy of a Polycomb factor and transcriptome reprogramming in response to JA revealed that Polycomb repression is involved in the repression of various JA-responsive genes.Taken together,our study reveals an important chromatin-based mechanism for JAZ-mediated transcriptional repression and JA signaling in plants.

MYC2： The Master in Action

Jasmonates （JAs） are plant hormones with essential roles in plant defense and development. The basic- helix-loop-helix （bHLH） transcription factor （TF） MYC2 has recently emerged as a master regulator of most aspects of the jasmonate （JA） signaling pathway in Arabidopsis. MYC2 coordinates JA-mediated defense responses by antagonistically regulating two different branches of the JA signaling pathway that determine resistance to pests and pathogens, respectively. MYC2 is required for induced systemic resistance （ISR） triggered by beneficial soil microbes while MYC2 function is targeted by pathogens during effector-mediated suppression of innate immunity in roots. Another notable function of MYC2 is the regulation of crosstalk between the signaling pathways of JA and those of other phytohormones such as abscisic acid （ABA）, salicylic acid （SA）, gibberellins （GAs）, and auxin （IAA）. MYC2 also regulates interactions between JA signaling and light, phytochrome signaling, and the circadian clock, MYC2 is involved in JA-regulated plant development, lateral and adventitious root formation, flowering time, and shade avoidance syndrome. Related bHLH TFs MYC3 and MYC4 also regulate both overlapping and distinct MYC2-regulated functions in Arabidopsis while MYC2 orthologs act as ＇master switches＇ that regulate JA-mediated biosynthesis of secondary metabolites. Here, we briefly review recent studies that revealed mechanistic new insights into the mode of action of this versatile TF.