Jasmonate perception and JAZ derepression (JAR1-COI1-JAZ-NINJA/TPL-MYC module)

Jasmonate signaling in vascular plants works by hormone-triggered derepression. Jasmonic acid is activated by the GH3-family jasmonoyl-amino acid conjugate synthetase JAR1, which adenylates JA and conjugates it to L-isoleucine to form jasmonoyl-L-isoleucine (JA-Ile), the bioactive hormone. JA-Ile is perceived by a co-receptor formed by the F-box/LRR protein COI1 and a JAZ (JASMONATE ZIM-domain) repressor: the hormone sits in an open pocket of the COI1 leucine-rich-repeat domain, is trapped by the Jas-motif degron of JAZ, and the complex is potentiated by inositol phosphate. COI1 is the substrate adaptor of an SCF E3 ubiquitin ligase (COI1-ASK1/ASK2-CUL1-RBX1), so hormone-dependent JAZ binding leads to JAZ polyubiquitination and 26S proteasome-dependent degradation. In the resting state, JAZ proteins bind the N-terminal JAZ-interaction domain of the bHLH transcription factors MYC2, MYC3 and MYC4 through their Jas motif, competitively blocking MYC recruitment of the Mediator subunit MED25; through their TIFY/ZIM domain they bind the adaptor NINJA, whose EAR motif recruits the Groucho/Tup1-type corepressor TOPLESS (TPL) and TPL-related proteins. JA-Ile-triggered JAZ degradation therefore removes both the MYC-blocking and the corepressor-recruiting activities, releasing MYC factors to activate jasmonate-responsive genes that control defense against insects and necrotrophic pathogens, wound responses, secondary metabolism and growth inhibition. Many JAZ genes are themselves MYC targets, providing negative feedback. Jasmonate biosynthesis upstream of JA (13-LOX, AOS, AOC, OPR3 and beta-oxidation), JA-Ile catabolism and JAZ-independent COI1 functions are outside this module.

Arabidopsis proteins are used as representative members; the COI1-JAZ-MYC module is conserved across land plants (in the liverwort Marchantia polymorpha COI1 perceives dinor-OPDA isomers rather than JA-Ile, so the JAR1 step is placed in vascular-plant context). JAZ1 (TIFY10A) is the representative JAZ; Arabidopsis has 13 JAZ proteins, most of which bind NINJA (JAZ7 and JAZ8 do not and carry their own EAR motifs). TOPLESS is referenced by its UniProt accession (Q94AI7, verified via UniProt REST); TPR2 and TPR3 also co-purify with NINJA. NINJA is named AFPH2 in UniProt (Q9SV55); NINJA is the standard Arabidopsis symbol. The SCF core subunits ASK1/ASK2, CUL1 and RBX1 are shared with other SCF ligases and are described rather than modeled as annotons. No PANTHER family ids are asserted: MYC2 and MYC3 are grouped by curator judgment as subgroup IIIe bHLH factors, not by a verified family id. The PANTHER family files for NINJA (PTHR31413 AFP HOMOLOG 2; UniProt places NINJA in subfamily PTHR31413:SF12) and JAR1 (PTHR31901 GH3 DOMAIN-CONTAINING PROTEIN; JAR1 in PTHR31901:SF5) were fetched for the gene reviews. Both proteins are modeled here as single GENE_PRODUCT participants, so neither family id is used as a module family descriptor. No production GO-CAM in gocams/index.tsv contains these Arabidopsis proteins (checked 2026-10-06). GO has no JA-Ile receptor-activity term; COI1 hormone perception uses hormone binding (GO:0042562), matching the COI1 review. NINJA and TPL are both given transcription corepressor activity; NINJA's more specific bridging (adaptor) role currently lacks a dedicated GO term.