Mediator subunit MED25 links the jasmonate receptor to transcriptionally active chromatin

Abstract

Jasmonoyl-isoleucine (JA-Ile), the active form of the plant hormone jasmonate (JA), is sensed by the F-box protein CORONATINE INSENSITIVE 1 (COI1), a component of a functional Skp-Cullin-F-box E3 ubiquitin ligase complex. Sensing of JA-Ile by COI1 rapidly triggers genome-wide transcriptional changes that are largely regulated by the basic helix-loop-helix transcription factor MYC2. However, it remains unclear how the JA-Ile receptor protein COI1 relays hormone-specific regulatory signals to the RNA polymerase II general transcriptional machinery. Here, we report that the plant transcriptional coactivator complex Mediator directly links COI1 to the promoters of MYC2 target genes. MED25, a subunit of the Mediator complex, brings COI1 to MYC2 target promoters and facilitates COI1-dependent degradation of jasmonate-ZIM domain (JAZ) transcriptional repressors. MED25 and COI1 influence each other's enrichment on MYC2 target promoters. Furthermore, MED25 physically and functionally interacts with HISTONE ACETYLTRANSFERASE1 (HAC1), which plays an important role in JA signaling by selectively regulating histone (H) 3 lysine (K) 9 (H3K9) acetylation of MYC2 target promoters. Moreover, the enrichment and function of HAC1 on MYC2 target promoters depend on COI1 and MED25. Therefore, the MED25 interface of Mediator links COI1 with HAC1-dependent H3K9 acetylation to activate MYC2-regulated transcription of JAresponsive genes. This study exemplifies how a single Mediator subunit integrates the actions of both genetic and epigenetic regulators into a concerted transcriptional program.is an oxylipin-derived plant hormone that regulates diverse aspects of plant immunity and development (1, 2). Decades of studies in the model plant Arabidopsis thaliana have revealed a core JA signaling module consisting of the F-box protein CORONATINE INSENSITIVE 1 (COI1) (3), a group of jasmonate-ZIM domain (JAZ) proteins (4-6), and the basic helixloop-helix transcription factor MYC2 (7, 8). COI1 forms a functional Skp-Cullin-F-box (SCF) E3 ubiquitin ligase SCF COI1 along with Cullin1 and Skp1-like1 (ASK1) (9, 10), MYC2 acts as a master transcription factor that differentially regulates diverse aspects of JA responses (11-13), and the JAZ proteins are substrates of SCF COI1 and serve as transcriptional repressors of MYC2 (4, 5, 14). The identification of jasmonoyl-isoleucine (JA-Ile) as the receptor-active form of the hormone, along with the discovery that sensing of JA-Ile involves formation of the SCF COI1 -JAZs coreceptor complex (4, 15-17), represented a breakthrough in our mechanistic understanding of JA signaling. In the absence of the hormone, JAZ repressors interact with and repress the activity of MYC2. In response to internal or external cues that trigger JAIle synthesis, elevated JA-Ile levels promote SCF COI1 -dependent degradation of JAZ repressors, and thereby activate (de-repress) the MYC2-directed transcriptional program. These discoveries imply that sensing of the active hormone is tightly linked to transcription of JA-responsive...

Regulation of flowering time by SPL10/MED25 module in Arabidopsis

“…Moreover, this mediator subunit contains a conserved glutamine (Q)‐rich poly‐track domain that may be involved in transcriptional activation by interacting with other activators (Rival et al ., ). Recently, HISTONE ACETYLTRANSFERASE 1 (HAC1), an evolutionarily conserved coactivator, has been reported to physically and functionally associate with MED25 to activate the expression of jasmonic acid responsive genes by H3K9 acetylation (An et al ., ). SPL10 also enhances the transcript levels of miR172b , AGL79, FUL , and AP1 during floral transition and shoot maturation (Shikata et al ., ; Wu et al ., ; Gao et al ., ; Fig.…”

The Important Function of Mediator Complex in Controlling the Developmental Transitions in Plants

“…These results suggest that MED17, MED18 and MED20 possibly modulate vegetative phase change by affecting the biogenesis of noncoding RNAs, including miR159 and miR172 [42]. Moreover, MED25 is considered as an integrator of JA-mediated transcriptional activation by interacting with MYC2 (a basic helix-loop-helix transcription factor) and HAC1 (HISTONE ACETYLTRANSFERASE1) [43,44]; and MED25 also couples alternative splicing of JAZ (JASMONATE ZIM-DOMAIN) genes with fine tuning of JA signaling [45]. Based on the important function of JA signaling in vegetative phase change, whether MED25 plays a role in the regulation of vegetative phase change needs to be studied further.…”

MYC2 regulates ARR16, a component of cytokinin signaling pathways, in Arabidopsis seedling development

“…In presence of the bioactive JA‐Ile (JA ligand jasmonyl‐isoleucine), JAZ (JASMONATE ZIM DOMAIN) repressor proteins forms a coreceptor complex with COI1 (CORONATINE‐INSENSITIVE1) which is the F‐box subunit of the SCF (Skp‐Cullin‐F‐box) complex leading to the proteasomal degradation of JAZ repressor via SCF COI protein complex. This, in turn releases the JAZ‐mediated transcriptional repression of MYC2 which causes the recruitment of other transcriptional activating proteins and chromatin‐modifying enzymes resulting in the transcriptional expression of JA‐responsive genes (An et al, ; Chen et al, ; Chini et al, , ; Fonseca et al, ; Goossens, Mertens, & Goossens, ; Kazan & Manners, ; Liu et al, ; Sheard et al, ; Thines et al, ; Yan et al, ).…”