The Arabidopsis Mediator Subunit MED25 Differentially Regulates Jasmonate and Abscisic Acid Signaling through Interacting with the MYC2 and ABI5 Transcription Factors

Abstract

Transcriptional regulation plays a central role in plant hormone signaling. At the core of transcriptional regulation is the Mediator, an evolutionarily conserved, multisubunit complex that serves as a bridge between gene-specific transcription factors and the RNA polymerase machinery to regulate transcription. Here, we report the action mechanisms of the MEDIATOR25 (MED25) subunit of the Arabidopsis thaliana Mediator in regulating jasmonate-and abscisic acid (ABA)-triggered gene transcription. We show that during jasmonate signaling, MED25 physically associates with the basic helix-loophelix transcription factor MYC2 in promoter regions of MYC2 target genes and exerts a positive effect on MYC2-regulated gene transcription. We also show that MED25 physically associates with the basic Leu zipper transcription factor ABA-INSENSITIVE5 (ABI5) in promoter regions of ABI5 target genes and shows a negative effect on ABI5-regulated gene transcription. Our results reveal that underlying the distinct effects of MED25 on jasmonate and ABA signaling, the interaction mechanisms of MED25 with MYC2 and ABI5 are different. These results highlight that the MED25 subunit of the Arabidopsis Mediator regulates a wide range of signaling pathways through selectively interacting with specific transcription factors.

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

“…That MED25 interacts with YID1/MED16 in vivo suggests that MED25 is probably a tail subunit. The interaction of MED25 with different transcription factors regulates multiple physiological processes (Elfving et al, 2011;Ou et al, 2011;Chen et al, 2012), because tail subunits usually interact with transcription factors through conformational changes (Casamassimi and Napoli, 2007;Toth-Petroczy et al, 2008;Meyer and Fu, 2012). The N-terminal vWF-A domain of MED25 was conserved among metazoans, Arabidopsis and other plant species.…”

“…MED25 interacts with transcription factors in the JA signaling pathway (Ou et al, 2011;C ßevik et al, 2012;Chen et al, 2012), with med25 mutants showing JA-mediated disease resistance phenotypes (Kidd et al, 2009). Therefore, the interaction between MED25 and the two crucial components (EIN3/EIL1) in the ethylene signaling pathway may affect ethylene-mediated plant growth (Alonso et al, 2003;Guo and Ecker, 2003;Potuschak et al, 2003).…”

“…Of the subunits tested in yeast, MED8, MED15, MED19, MED21, MED25, MED28, MED32, MED34, MED36 and MED37, only MED25 interacted with YID1/ MED16 ( Figure 3a). MED25 is an important Mediator subunit having multiple functions in the defense response and organ development (Kidd et al, 2009;Xu and Li, 2011;Chen et al, 2012). Several transcription factors in various pathways have been reported to interact with MED25 (Ou et al, 2011;C ßevik et al, 2012).…”

MED18 interaction with distinct transcription factors regulates multiple plant functions

“…The data indicate that MED18 functions independently of JA signalling or may suppress some responses leading to PDF1.2 gene expression. This is unlike MED25 and MED8 subunits that regulate plant defence through JA signalling 7,22 . Thus, MED18 immune response function is mechanistically distinct from previously described Mediator subunits or other defence regulators.…”

“…MED18 has been shown to play a role in flowering time and flower organ identity 6 . MED25 has been implicated in diverse functions, including suppression of abscisic acid (ABA) but activation of jasmonic acid (JA) signalling 7,8 . MED21 interacts with HUB1 (HISTONE MONOUBIQUITINATION1), an E3 ligase required for ubiquitination of histone H3, modulating plant immune reponses to fungal infection.…”