Abstract
Jasmonate (JA) signalling is mediated by the JASMONATE-ZIM DOMAIN (JAZ) repressor proteins, which are degraded upon JA perception to release downstream responses. The ZIM protein domain is characteristic of the larger TIFY protein family. It is currently unknown if the atypical member TIFY8 is involved in JA signalling. Here we show that the TIFY8 ZIM domain is functional and mediated interaction with PEAPOD proteins and NINJA. TIFY8 interacted with TOPLESS through NINJA and accordingly acted as a transcriptional repressor. TIFY8 expression was inversely correlated with JAZ expression during development and after infection with Pseudomonas syringae. Nevertheless, transgenic lines with altered TIFY8 expression did not show changes in JA sensitivity. Despite the functional ZIM domain, no interaction with JAZ proteins could be found. In contrast, TIFY8 was found in protein complexes involved in regulation of dephosphorylation, deubiquitination and O-linked N-acetylglucosamine modification suggesting an important role in nuclear signal transduction.
Highlights
Jasmonates (JAs) are plant-specific hormones that regulate processes such as vegetative growth, cell cycle progression, trichome formation, senescence, male fertility and responses to both abiotic and biotic stresses
The TIFY8 protein is an atypical TIFY protein A phylogenetic tree based on the Zinc-finger protein expressed in Inflorescence Meristem (ZIM) domain sequence shows that the TIFY8 ZIM domain is closely related to that of the JASMONATE-ZIM DOMAIN (JAZ) proteins, but that TIFY8 lacks additional domains present in the TIFY family such as the CCT, C2C2-GATA, EAR, Jas or PPD domains (Figure 1) [20]
TIFY8 is not involved in JA signalling Prompted by the TIFY-family phylogeny (Figure S1) and the interesting developmental expression pattern of TIFY8, which is the inverse of many JAZ genes (Figure S2), we investigated a possible role of TIFY8 in JA signalling
Summary
Jasmonates (JAs) are plant-specific hormones that regulate processes such as vegetative growth, cell cycle progression, trichome formation, senescence, male fertility and responses to both abiotic and biotic stresses. The presence of JA-Ile targets JAZ proteins for proteasomal degradation, releasing the transcription factors to regulate JAdependent gene expression [17,18]. The different domains present in the JAZ proteins (Figure 1) provide the specificity for protein-protein interactions that determine the differential formation of complexes in the absence or presence of the hormone [18]. All 12 JAZ proteins possess a Cterminal Jas domain [16], which mediates interaction with several transcription factors, including several bHLH- and R2R3-MYBtype factors that regulate different JA-dependent responses [18]. JA-Ile or COR can act as a ‘‘molecular glue’’ between COI1 and the JAZ proteins [23,24,25,26] This interaction targets the JAZ proteins for 26S-mediated proteasomal degradation. Overexpression of TIFY8 did not lead to altered JA responses but was correlated with reduced root growth
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