Auxin-dependent compositional change in Mediator in ARF7- and ARF19-mediated transcription

Abstract

Mediator is a multiprotein complex that integrates the signals from transcription factors binding to the promoter and transmits them to achieve gene transcription. The subunits of Mediator complex reside in four modules: the head, middle, tail, and dissociable CDK8 kinase module (CKM). The head, middle, and tail modules form the core Mediator complex, and the association of CKM can modify the function of Mediator in transcription. Here, we show genetic and biochemical evidence that CKM-associated Mediator transmits auxindependent transcriptional repression in lateral root (LR) formation. The AUXIN/INDOLE 3-ACETIC ACID 14 (Aux/IAA14) transcriptional repressor inhibits the transcriptional activity of its binding partners AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 by making a complex with the CKM-associated Mediator. In addition, TOPLESS (TPL), a transcriptional corepressor, forms a bridge between IAA14 and the CKM component MED13 through the physical interaction. ChIP assays show that auxin induces the dissociation of MED13 but not the tail module component MED25 from the ARF7 binding region upstream of its target gene. These findings indicate that auxininduced degradation of IAA14 changes the module composition of Mediator interacting with ARF7 and ARF19 in the upstream region of their target genes involved in LR formation. We suggest that this regulation leads to a quick switch of signal transmission from ARFs to target gene expression in response to auxin. M ediator is a multiprotein complex that relays integrated information from transcriptional factors to RNA polymerase II (RNAPII) (1-3). Mediator consists of ∼25-30 subunits, which are organized into three modules forming the core Mediator (head, middle, and tail) and the dissociable CDK8 kinase module (CKM) (3, 4). The Mediator structure, subunit organization, and RNAPII interaction are conserved across eukaryotes, whereas Mediator is not a fixed complex. Structural analyses show that Mediator conformation and module organization are altered in accordance with the interaction with RNAPII (5, 6). RNAPII interacts with the middle module of the core Mediator, leading to a conformation change that could facilitate holoenzyme formation. CKM binds to the middle module, which interferes with the interaction of RNAPII with the core Mediator in vitro. In addition, recent accumulating evidence has shown a wide range of Mediator functions involving in almost all stages of RNAPII transcription, such as epigenetic regulation, transcriptional elongation, termination, mRNA processing, noncoding RNA activation, and superenhancer formation (3, 7). In Arabidopsis, the core Mediator is composed of more than 21 subunits (8), and CKM

Expression of RSOsPR10 in rice roots is antagonistically regulated by jasmonate/ethylene and salicylic acid via the activator OsERF87 and the repressor OsWRKY76, respectively

“…The results of the present study also showed that the promoter region, at least 3 kb, of RSOsPR10 drives root‐specific gene expression in lateral root primordia and at the basal region of growing lateral roots (Figure ). Several other studies have suggested that JA and auxin signaling and their crosstalk are important in the formation and growth of lateral roots (Ito et al., ; Lu et al., ; Sun et al., ). Therefore, we hypothesize that RSOsPR10 is one of the key molecules in root development.…”

Functional analysis of molecular interactions in synthetic auxin response circuits

“…TPL recruitment and its own multimerization could stabilize ARF-IAA interactions, which would explain why IAAs expressed without TPL fusions are poor repressors in yeast. It is also possible that binding of the IAA to the ARF could lead to conformational changes in the flexible middle region of the ARF that blocks recruitment of coactivators (33,39) or changes the module composition of core transcriptional machinery like the Mediator complex (40). Phosphorylation of the middle region in ARF7 and ARF19 has been shown to inhibit IAA interaction (41), indicating that signal integration from other pathways may take advantage of a link between an IAA interaction and the activity of the ARF middle region.…”

Accelerating structure‐function mapping using the ViVa webtool to mine natural variation

“…It has recently been shown that the middle region of ARF5 interacts with the SWI/SNF chromatin remodeling ATPases BRAMA and SPLAYED, possibly to reduce nucleosome occupancy and allow for the recruitment of transcription machinery (Wu et al., ). Additionally, ARF7 interacts with Mediator subunits, directly tethering transcriptional activation machinery to its binding sites in the chromosome (Ito et al., ). Class B and C ARF s are historically categorized as repressor ARF s, although the mechanism through which they confer repression has not been identified.…”