Cevik V, Kidd BN, Zhang P, Hill C, Kiddle S, Denby KJ, Holub EB, Cahill DM, Manners JM, Schenk PM, Beynon J, Kazan K

The PHYTOCHROME AND FLOWERING TIME1 (PFT1) gene encoding the MEDIATOR25 (MED25) subunit of the eukaryotic Mediator complex is a positive regulator of jasmonate- (JA) responsive gene expression in Arabidopsis thaliana. Based on the function of the Mediator complex as a bridge between DNA-bound transcriptional activators and the RNA polymerase II ...

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complex, MED25 has been hypothesized to function in association with transcriptional regulators of the JA pathway. However, it is currently not known mechanistically how MED25 functions to regulate JA-responsive gene expression. In this study, we show that MED25 physically interacts with several key transcriptional regulators of the JA signaling pathway, including the AP2/ERF transcription factors OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF59 (ORA59) and ETHYLENE RESPONSE FACTOR1 (ERF1) as well as the master regulator MYC2. Physical interaction detected between MED25 and four group IX AP2/ERF TFs was shown to require the Activator Interaction Domain (ACID) of MED25 as well as the recently discovered CMIX-1/EDLL transcription activation motif of MED25-interacting AP2/ERFs. Using transcriptional activation experiments, we also show that ORA59- and ERF1-dependent activation of PLANT DEFENSIN1.2 (PDF1.2) as well as MYC2-dependent activation of VEGETATIVE STORAGE PROTEIN1 (VSP1) requires a functional MED25. In addition, MED25 is required for MYC2-dependent repression of pathogen defense genes. These results suggest an important role for MED25 as an integrative hub within the Mediator complex during the regulation of JA-associated gene expression.

Date: Jul. 22, 2012

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