Purification of a Plant Mediator from Arabidopsis thaliana Identifies PFT1 as the Med25 Subunit (original) (raw)
Related papers
Tissue specific expression profile of Mediator genes in Arabidopsis
Plant Signaling & Behavior, 2013
Mediator was discovered in yeast as a necessary component for transcription of a protein coding gene. 1,2 Later on, Mediator was purified and characterized to be a gigantic multiprotein complex required by RNA polymerase II for the transcription of its target genes. 3-5 It was found to play important role in facilitating the assembly of the preinitiation complex. 6-8 Genetic, biochemical and bioinformatic analyses revealed its existence in all the eukaryotes ranging from simple unicellular yeast to complex multicellular mammals and plants. 8-11 In yeast, there are 25 subunits which make Mediator, whereas in animals and plants the number is higher. 11,12 Biochemical and biophysical studies in fungi and metazoans confirmed the modular structure of this complex, wherein the subunits compose four different modules namely Head, Middle, Tail and Kinase. 5,8,13-15 Head, Middle and Tail constitute the core part of the complex, whereas the Kinase module reversibly associates with the core part. Subunits constituting the Head and Middle modules are found to interact with RNA pol II and components of transcriptional machinery, whereas subunits of Tail module establish contact with diverse transcription factors. 13,16-18 Thus, Mediator provides an interface to relay the regulatory signals from the transcriptional regulators to the transcriptional machinery. The subunits of Kinase module can interact with the subunits of the Head and Middle modules, and so affect the interaction between the complex and the RNA pol II. That is why in many cases, presence of Kinase module in the Mediator was found to be associated with the repression of the gene expression. 19 Mediator is a gigantic multiprotein complex required for transcription of almost all the protein coding genes. In this report, we have analyzed the transcript abundance of 31 Med genes in different tissues of Arabidopsis. Our analysis revealed the tissue specific differential expression profile of many Med subunit genes suggesting they might be contributing in the formation, maturation or function of that specific tissue. Moreover, we also found increase or decrease in the expression level of several Med subunits during the same duration of specific processes (for example flowering) indicating probable enrichment of a particular arrangement of selected subunits during that process. Thus, this study suggests that not only specific Med subunits have functional relevance in specific processes, but specific arrangements of Med subunits might also play significant role in some processes in Arabidopsis or other plants.
Frontiers in Plant Science, 2015
Basic transcriptional machinery in eukaryotes is assisted by a number of cofactors, which either increase or decrease the rate of transcription. Mediator complex is one such cofactor, and recently has drawn a lot of interest because of its integrative power to converge different signaling pathways before channeling the transcription instructions to the RNA polymerase II machinery. Like yeast and metazoans, plants do possess the Mediator complex across the kingdom, and its isolation and subunit analyses have been reported from the model plant, Arabidopsis. Genetic, and molecular analyses have unraveled important regulatory roles of Mediator subunits at every stage of plant life cycle starting from flowering to embryo and organ development, to even size determination. It also contributes immensely to the survival of plants against different environmental vagaries by the timely activation of its resistance mechanisms. Here, we have provided an overview of plant Mediator complex starting from its discovery to regulation of stoichiometry of its subunits. We have also reviewed involvement of different Mediator subunits in different processes and pathways including defense response pathways evoked by diverse biotic cues. Wherever possible, attempts have been made to provide mechanistic insight of Mediator's involvement in these processes.
Regulation of transcription in plants
The developmental switch from vegetative to reproductive growth – also known as flowering – is a critical transition in the life cycle of flowering plants. This transition is developmentally delayed until the plant has reached a stage of growth sufficient to support fruit and seed production. Superimposed on developmental regulation is the ability to delay or initiate flowering in response to environmental cues, such as photoperiod and temperature, in order to take full advantage of a seasonal climate optimal for reproduction. The switch to flowering involves the activation of a select set of key regulatory genes that initiate extensive changes in gene activity in the shoot apical meristem (Figure 9.1). Cumulative research has revealed that the molecular mechanisms of flower- ing are vastly complex and touch on most of the known eukaryotic mechanism of transcriptional regulation. This review will focus on transcriptional aspects of the individual regulatory pathways that have been defined to regulate flowering in the reference plant Arabidopsis thaliana, as well as how these pathways are integrated to activate genes that force inflorescence fate on the shoot apical meristem.
Development, 2019
Mediator is a large multiprotein complex that is required for the transcription of most, if not all, genes transcribed by RNA Polymerase II. A core set of subunits is essential to assemble a functional Mediator in vitro and, therefore, the corresponding loss-of-function mutants are expected to be lethal. The MED30 subunit is essential in animal systems, but is absent in yeast. Here, we report that MED30 is also essential for both male gametophyte and embryo development in the model plant Arabidopsis thaliana. Mutant med30 pollen grains were viable and some were able to germinate and target the ovules, although the embryos aborted shortly after fertilization, suggesting that MED30 is important for the paternal control of early embryo development. When gametophyte defects were bypassed by specific pollen complementation, loss of MED30 led to early embryo development arrest. Later in plant development, MED30 promotes flowering through multiple signaling pathways; its downregulation led to a phase change delay, downregulation of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 (SPL3), FLOWERING LOCUS T (FTI) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), and upregulation of FLOWERING LOCUS C (FLC).
The Plant journal : for cell and molecular biology, 2012
Two aspects of light are very important for plant development: the length of the light phase or photoperiod and the quality of incoming light. Photoperiod detection allows plants to anticipate the arrival of the next season, whereas light quality, mainly the red to far-red ratio (R:FR), is an early signal of competition by neighbouring plants. phyB represses flowering by antagonising CO at the transcriptional and post-translational levels. A low R:FR decreases active phyB and consequently increases active CO, which in turn activates the expression of FT, the plant florigen. Other phytochromes like phyD and phyE seem to have redundant roles with phyB. PFT1, the MED25 subunit of the plant Mediator complex, has been proposed to act in the light-quality pathway that regulates flowering time downstream of phyB. However, whether PFT1 signals through CO and its specific mechanism are unclear. Here we show that CO-dependent and -independent mechanisms operate downstream of phyB, phyD and ph...
Uncovering Factors and Molecular Mechanisms in Transcriptional Regulation in Arabidopsis thaliana
2012
Cell fate specification in development requires transcription factors for proper regulation of gene expression. In Arabidopsis, transcription factors encoded by four classes of homeotic genes, A, B, C, and E, act in a combinatorial manner to control proper floral organ identity. The A-class gene APETALA2 (AP2) promotes sepal and petal identities in whorls 1 and 2 and restricts the expression of the C-class gene AGAMOUS (AG) from whorls 1 and 2. However, it is unknown how AP2 performs these functions. Unlike the other highly characterized floral homeotic proteins containing MADS domains, AP2 has two DNA binding domains referred to as the AP2 domains and its DNA recognition sequence is still unknown. Here, we show that AP2 binds a noncanonical AT-rich target sequence, and utilizing a GUS reporter system, we demonstrate that the presence of this sequence in the AG 2 nd intron is important for the restriction of AG expression in vivo. Furthermore, we show that AP2 binds the AG 2 nd intron and directly regulates AG expression through this sequence element. Computational analysis reveals that the binding site is highly conserved in the second intron of AG orthologs throughout Brassicaceae. By uncovering a biologically relevant AT-rich target sequence, this work shows that AP2 domains have wide-ranging target specificities and provides a 2 missing link in the mechanisms underlying flower development. It also sets the foundation for understanding the basis of the broad biological functions of AP2 in Arabidopsis as well as the divergent biological functions of AP2 orthologs in dicotyledonous plants.
Frontiers in Plant Science, 2021
The Mediator complex controls transcription of most eukaryotic genes with individual subunits required for the control of particular gene regulons in response to various perturbations. In this study, we reveal the roles of the plant Mediator subunits MED16, MED14, and MED2 in regulating transcription in response to the phytohormone abscisic acid (ABA) and we determine which cis elements are under their control. Using synthetic promoter reporters we established an effective system for testing relationships between subunits and specific cis-acting motifs in protoplasts. Our results demonstrate that MED16, MED14, and MED2 are required for the full transcriptional activation by ABA of promoters containing both the ABRE (ABA-responsive element) and DRE (drought-responsive element). Using synthetic promoter motif concatamers, we showed that ABA-responsive activation of the ABRE but not the DRE motif was dependent on these three Mediator subunits. Furthermore, the three subunits were requi...