The Mediator Complex Subunit PFT1 Is a Key Regulator of Jasmonate-Dependent Defense inArabidopsis   

Abstract

Jasmonate signaling plays an important role in both plant defense and development. Here, we have identified a subunit of the Mediator complex as a regulator of the jasmonate signaling pathway in Arabidopsis thaliana. The Mediator complex is a conserved multiprotein complex that acts as a universal adaptor between transcription factors and the RNA polymerase II transcriptional machinery. We report that the PHYTOCHROME AND FLOWERING TIME1 (PFT1) gene, which encodes the MEDIATOR25 subunit of Mediator, is required for jasmonate-dependent defense gene expression and resistance to leaf-infecting necrotrophic fungal pathogens. Conversely, PFT1 appears to confer susceptibility to Fusarium oxysporum, a root-infecting hemibiotrophic fungal pathogen known to hijack jasmonate responses for disease development. Consistent with this, jasmonate gene expression was suppressed in the pft1 mutant during infection with F. oxysporum. In addition, a wheat (Triticum aestivum) homolog of PFT1 complemented the defense and the developmental phenotypes of the pft1 mutant, suggesting that the jasmonate signaling functions of PFT1 may be conserved in higher plants. Overall, our results identify an important control point in the regulation of the jasmonate signaling pathway within the transcriptional machinery.

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

“…In Arabidopsis, three subunits in the head module of the Mediator complex, MED17, MED18 and MED20, are involved in development by regulating the expression of micro-RNA biosynthesis genes . Two subunits, MED25 and MED8 (a head module subunit), which positively regulate flowering time and disease resistance (Kidd et al, 2009), antagonistically regulate flower organ size Li, 2011, 2012), and regulate root development via two independent pathways (Sundaravelpandian et al, 2013). Yid1/med16 and med25 displayed similar iron-associated phenotypes, with YID1/MED16 directly interacting with MED25, suggesting that YID1/ MED16 and MED25 may synergistically regulate iron homeostasis in plants.…”

“…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).…”

“…MED14 was involved in leaf development and leaf cell proliferation (Autran et al, 2002) and MED33 was required for phenylpropanoid homeostasis (Bonawitz et al, 2012). MED25 was important for plant disease resistance, flowering and organ size (Cerdan and Chory, 2003;Kidd et al, 2009;Xu and Li, 2011), whereas MED17, MED18 and MED20 in the head module affected micro-RNA production . Mediator subunits are involved in pleiotropic physiological processes, suggesting that the Mediator complex may trigger physiological functions by interacting with different transcription factors through different subunits.…”

The Mediator Complex in Plants: Structure, Phylogeny, and Expression Profiling of Representative Genes in a Dicot (Arabidopsis) and a Monocot (Rice) during Reproduction and Abiotic Stress

“…A biochemical screen identified Arabidopsis PFT1 as Med25 (Bäckströ m et al, 2007). The PFT1 negatively regulates the phytochrome signaling pathway (Wollenberg et al, 2008), regulating flowering in response to light quality (Cerdán and Chory, 2003) and by acting as a positive regulator of jasmonic acid signaling, which regulates plant defense responses during fungal pathogen infection (Kidd et al, 2009). The expression profile of AtMed25_1 revealed very similar transcript abundance in flower as compared with vegetative tissues, augmenting by approximately 2-fold in the S9 and S10 seed stages.…”