NINJA connects the co-repressor TOPLESS to jasmonate signalling

Abstract

Jasmonoyl-isoleucine (JA-Ile) is a plant hormone that regulates a broad array of plant defence and developmental processes1–5. JA-Ile-responsive gene expression is regulated by the transcriptional activator MYC2 that interacts physically with the jasmonate ZIM-domain (JAZ) repressor proteins. Upon JA-Ile perception, JAZ proteins are degraded and JA-Ile-dependent gene expression is activated6,7. The molecular mechanisms by which JAZ proteins repress gene expression remain unknown. Here we show that the JAZ proteins recruit the Groucho/Tup1-type co-repressor TOPLESS (TPL)8 and TPL-related proteins (TPRs) through a previously uncharacterized adaptor protein, designated Novel INteractor of JAZ (NINJA). NINJA acts as a transcriptional repressor of which the activity is mediated by a functional TPL-binding EAR repression motif. Accordingly, both NINJA and TPL proteins function as negative regulators of jasmonate responses. Our results point to TPL proteins as general co-repressors that affect multiple signalling pathways through the interaction with specific adaptor proteins. This new insight reveals how stress- and growth-related signalling cascades use common molecular mechanisms to regulate gene expression in plants.

A bHLH-Type Transcription Factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1, Acts as a Repressor to Negatively Regulate Jasmonate Signaling inArabidopsis

“…Recent advances have established a simple transcriptional regulatory model for JA signaling consisting of MYC2, JAZs, NINJA, TOPLESS, and SCF COI1 complexes (Chini et al, 2007;Thines et al, 2007;Yan et al, 2007;Pauwels et al, 2010). However, new insights have recently emerged on the regulatory mechanisms of JA signaling, including identification of JAZ binding partners, and the influence of circadian rhythms and hormonal crosstalk (Hou et al, 2010;Qi et al, 2011;Song et al, 2011;Goodspeed et al, 2012;Hong et al, 2012;Shin et al, 2012;Yang et al, 2012).…”

“…Identification of JASMONATE ZIM-DOMAIN (JAZ) proteins as targets of the E3 ligase SCF COI1 also facilitated elucidation of the JA signaling pathway (Chini et al, 2007;Thines et al, 2007). In the absence of JA, the activity of transcription factors that regulate JA responses is repressed by binding of JAZ and a corepressor complex consisting of NOVEL INTERACTOR OF JAZ (NINJA) and TOPLESS (Chini et al, 2007;Thines et al, 2007;Yan et al, 2007;Pauwels et al, 2010). When the bioactive JA-Ile conjugate is produced in response to endogenous and exogenous stimuli, formation of a COI1-JAZ coreceptor complex is promoted by JA-Ile, and JAZ is polyubiquitinated by the E3 ligase SCF COI1 and is then degraded by the 26S proteasome pathway (Chini et al, 2007;Thines et al, 2007;Katsir et al, 2008;Fonseca et al, 2009;Sheard et al, 2010).…”

APETALA2/ETHYLENE RESPONSE FACTOR and basic helix–loop–helix tobacco transcription factors cooperatively mediate jasmonate‐elicited nicotine biosynthesis

“…The Y2H analysis was performed as described (Pauwels et al, 2010) with modifications. Gateway-compatible versions of pGADT7 and pGBKT7 (Clontech, http://www.clontech.com/) were used as destination vectors, co-transformed in the yeast strain PJ69-4A and selected on synthetic defined (SD)-Leu-Trp agar medium.…”

“…The NbbHLHs are related to the Arabidopsis (Arabidopsis thaliana) bHLH transcriptional activators MYC2, MYC3 and MYC4 that are essential elements of the conserved plant JA signalling module (Lorenzo et al, 2004;Fonseca et al, 2009;Ferná ndez-Calvo et al, 2011). In the absence of JA hormone, the Arabidopsis JASMONATE ZIM-DOMAIN JAZ transcriptional repressor proteins bind MYC2 and recruit a co-repressor complex, composed of the NOVEL INTERAC-TOR OF JAZ (NINJA) and TOPLESS proteins, that blocks MYC2 activity (Chini et al, 2007;Thines et al, 2007;Pauwels et al, 2010). In the presence of bioactive JAs, CORONATINE INSENSITIVE1 (COI1) targets the JAZ proteins for degradation, which in turn releases MYC2.…”

The Arabidopsis Mediator subunit MED16 regulates iron homeostasis by associating with EIN3/EIL1 through subunit MED25

“…Furthermore, EIN3 and EIL1 are linked to ethylene signaling in the jasmonic acid (JA) signaling pathways. EIN3 and EIL1 interact with JAZ proteins that are associated with NINJA protein, recruiting TOP-LESS to induce gene expression in the JA signaling pathway (Pauwels et al, 2010;Zhu et al, 2011).…”