Social Network: JAZ Protein Interactions Expand Our Knowledge of Jasmonate Signaling

Abstract

Members of the family of JASMONATE ZIM-DOMAIN (JAZ) proteins are key regulators of the jasmonate (JA) hormonal response. The 12-member family is characterized by three conserved domains, an N-terminal domain, a TIFY-containing ZINC-FINGER EXPRESSED IN INFLORESCENCE MERISTEM domain, and a C-terminal Jas domain. JAZ proteins regulate JA-responsive gene transcription by inhibiting DNA-binding transcription factors in the absence of JA. JAZ proteins interact in a hormone-dependent manner with CORONATINE INSENSITIVE 1 (COI1), the recognition component of the E3 ubiquitin ligase, SCF(COI1), resulting in the ubiquitination and subsequent degradation of JAZs via the 26S proteasome pathway. Since their discovery in 2007, JAZ proteins have been implicated in protein-protein interactions with multiple transcription factors. These studies have shed light on the mechanism by which JAZs repress transcription, are targeted for degradation, modulate the JA signaling response, and participate in crosstalk with other hormone signaling pathways. In this review, we will take a close look at the recent discoveries made possible by the characterization JAZ protein-protein interactions.

Keywords: Arabidopsis; JAZ; hormone action; jasmonate.

Figure 1

JAZ proteins bind transcription factors (TFs) and recruit co-repressors, including NINJA and TOPLESS (TPL), to repress gene transcription in the absence of the active form of jasmonate (JA), JA–Ile (black diamond). In the presence of JA–Ile, the hormone facilitates interaction between JAZ proteins and the F-box protein COI1, the recognition component of the E3 ubiquitin ligase SCF^COI1. As a result, JAZ proteins are ubiquitinated (orange circles) and subsequently degraded in the 26S proteasome releasing TFs from inhibition and activating JA-responsive gene transcription.

Figure 2

Schematic of JAZ1 interaction domains. Colored boxes indicate conserved domains with the sequence, below. Proteins proposed to bind within each domain are listed below. The yellow bar indicates residues sufficient for COI1 binding. Red stars mark residues required for forming homo- and/or heterodimers (ZIM domain). Green stars mark residues required for COI1 binding (Jas domain). The black bars over bold residues mark a conserved EAR-like motif (NT domain) and a proposed nuclear localization signal (Jas domain). The black bar over residues 134–155 marks a conserved region with no ascribed function. References: ¹Hou et al. (2011), ²Zhu et al. (2011), ³Chini et al. (2009), ⁴Chung and Howe (2009), ⁵Pauwels et al. (2009), ⁶Chung et al. (2010), ⁷Chini et al. (2007), ⁸Melotto et al. (2008), ⁹Sheard et al. (2011), ¹⁰Niu et al. (2011), ¹¹Cheng et al. (2011), ¹²Fernández-Calvo et al. (2011), ¹³Song et al. (2011), ¹⁴Qi et al. (2011), ¹⁵Grunewald et al. (2009).

Figure 3

(A) Alignment of the semi-conserved EAR-like motif present in the NT domain of select JAZ proteins. Specific residues comprising the EAR-like motif are shown in bold. Red residues indicate the key (leucine or similar). (B) Alignment of the C-terminal portion of JAZs sufficient for NINJA. The TIFYXG motif required interaction (Pauwels et al., 2009) is underlined. This contains an N residue (red) in JAZ7 and JAZ8, the only two JAZs incapable of NINJA interaction. Residues conserved across all six JAZs shown are bold, residues conserved in JAZ1, JAZ2, JAZ5, and JAZ6, but not JAZ7 and JAZ8 are colored blue or green, respectively.