**5. Jasmonates signal perception and transduction pathway**

Several transcription factors (TFs), repressors, up- regulation and down-regulation of certain genes, and members of ubiquitin-proteasome complexes are involved in JA signal perception and transduction pathway (**Figure 5**). Different independent studies [21, 22] with GC-MS and HPLC analyses in *A. thaliana* revealed that (+)-7-iso-JA-L-Ile is the only natural and direct JA-signaling ligand in plants.

The Skp1/Cullin/F-box (SCF) complex is of proteinous type and is the ubiquitinproteasome complex. In jasmonate signal transduction pathway *coronatine insensitive1* (*COI1*)*,* the locus encodes an F-box protein that associates with its other counterparts, SKP1, Cullin, and Rbx proteins, to form an E3 ubiquitin ligase [23]. So *COI1* is found to be the jasmonate receptor in signaling pathway. In 2007, [22, 24, 25] scientists in independent research found new family of proteins called jasmonate zim-domain (JAZ) proteins in Arabidopsis, which were found to be the key negative regulator of JA signaling and act as substrate for SCF*COI1* E3 ubiquitin ligase complex. About 12 JAZ proteins were present in *A. thaliana* and contain N-terminal domain, a highly conserved C-terminal Jas domain that mediates the interaction with the *COI1* and several transcription factors, and the conserved protein–protein interaction domain, the ZIM (TIFY) domain that helps in JAZ dimerization and interaction with novel interactor of JAZ (NINJA).

Moreover, the interaction of *COI1* with the Jas domain of JAZ proteins in the presence of JA-Ile forms the co-receptor complex [26] SCF*COI1*, E3 ubiquitin ligase complex, JAZ degrons (*JAZ1* to *JAZ12*) and IP5 form the co-receptor complex and found to be true jasmonates receptors [27].

**Figure 5.**

*Signal transduction pathway of jasmonic acid.*

A number of co-repressors also play their role simultaneously in signal transduction pathway. Corepressors in transcriptional regulators inhibit transcription initiation. TOPLESS (TPL) and TPL-related proteins (TPRs) are members of Groucho/ Tup1 co-repressor family that causes histone deacetylation and demethylation which resulted in chromatin modification, eventually mediated repression of genes. [10]. Interaction of TPL with JAZ proteins takes place via ethylene response factor (ERF)-associated amphiphilic repression (EAR) motif. Those JAZ proteins having absence of repression motif recruit TPL through an adapter protein called novel interactor of JAZ (NINJA) [28].

MYC2 the master regulator of many biological processes is a bHLH transcription factor mediating the transcriptional regulation of JA. Other transcription factors that controls JA mediated signaling are MYC3, MYC4, MYB, GL3, EGL3 AP, GL1, etc.
