The Functions of Mediator in Candida albicans Support a Role in Shaping Species-Specific Gene Expression

et al. (2012) The Functions of Mediator in Candida albicans Support a Role in Shaping Species- Specific Gene Expression. PLoS Genet 8(4): e1002613. doi:10.1371/journal.pgen.1002613 The Functions of Mediator in Candida albicans Support a Role in Shaping Species-Specific Gene Expression Nathalie Uwamahoro 0 Yue Qu 0 Branka Jelicic 0 Tricia L. Lo 0 Cecile Beaurepaire 0 Farkad Bantun 0 Tara Quenault 0 Peter R. Boag 0 Georg Ramm 0 Judy Callaghan 0 Traude H. Beilharz 0 Andre Nantel 0 Anton Y. Peleg 0 Ana Traven 0 Randall Morse, Wadsworth Center, United States of America 0 1 Department of Biochemistry and Molecular Biology, Monash University , Clayton, Victoria , Australia , 2 Department of Microbiology, Monash University , Clayton, Victoria , Australia , 3 Biotechnology Research Institute, National Research Council of Canada , Montreal, Quebec , Canada , 4 Monash Micro Imaging , Monash University , Clayton , Australia , 5 Department of Infectious Diseases, The Alfred Hospital , Melbourne, Victoria , Australia The Mediator complex is an essential co-regulator of RNA polymerase II that is conserved throughout eukaryotes. Here we present the first study of Mediator in the pathogenic fungus Candida albicans. We focused on the Middle domain subunit Med31, the Head domain subunit Med20, and Srb9/Med13 from the Kinase domain. The C. albicans Mediator shares some roles with model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, such as functions in the response to certain stresses and the role of Med31 in the expression of genes regulated by the activator Ace2. The C. albicans Mediator also has additional roles in the transcription of genes associated with virulence, for example genes related to morphogenesis and gene families enriched in pathogens, such as the ALS adhesins. Consistently, Med31, Med20, and Srb9/ Med13 contribute to key virulence attributes of C. albicans, filamentation, and biofilm formation; and ALS1 is a biologically relevant target of Med31 for development of biofilms. Furthermore, Med31 affects virulence of C. albicans in the worm infection model. We present evidence that the roles of Med31 and Srb9/Med13 in the expression of the genes encoding cell wall adhesins are different between S. cerevisiae and C. albicans: they are repressors of the FLO genes in S. cerevisiae and are activators of the ALS genes in C. albicans. This suggests that Mediator subunits regulate adhesion in a distinct manner between these two distantly related fungal species. - Funding: AT was supported by an Australian National Health and Medical Research council (NH&MRC) Fellowship and a Fellowship from the Monash University Faculty of Medicine. TQ is supported by an Australian Postgraduate award, and FB is supported by a PhD scholarship from the Saudi Arabian government. THB and YQ are supported by fellowships from the Australian Research Council (ARC). PRB and AYP are supported by grants and fellowships from the NH&MRC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. . These authors contributed equally to this work. The transcription factor complex Mediator is associated with RNA polymerase II and it has essential roles in transcription ([1], reviewed in [2]). The yeast Mediator is composed of 25 subunits, which are structurally and functionally organized into four modules [38]. The core complex is comprised of the Head, Middle and Tail domains [36]. A fourth, Kinase domain is associated with Mediator under some conditions ([911]; reviewed in [2]). The core Mediator has a positive role in transcription, while the Kinase domain mainly functions in repression [2]. The roles of Mediator in transcription are complex [2,12]. Mediator interacts with gene-specific transcription factors and RNA polymerase II and mediates polymerase-activator interactions and formation of the pre-initiation complex (reviewed in [2,12,13]). In addition to activated transcription, Mediator also stimulates basal transcription [1,14,15]. Further proposed roles for Mediator are in post-initiation steps [12,1619], re-initiation during multiple rounds of transcription [20] and regulation of chromatin structure [12,21,22]. Two recent reports showed an additional role for the core Mediator in sub-telomeric gene silencing [23,24]. In addition to these versatile roles in gene transcription, Mediator also appears to be a central integrative hub for the regulation of gene expression by physiological signals [12]. Examples from yeast include regulation of the Kinase domain by the Ras/PKA pathway via phosphorylation of the Srb9/Med13 subunit [25], and control over the expression of ironresponsive genes by an interplay between the Tail subunit Med2, which has a positive role, and the Kinase domain that phosphorylates Med2 to inhibit its function [7,26]. The multisubunit Mediator complex emerged early in the evolution of eukaryotes, and the versatility of its functions and its role as an integrative platform for cell physiology could have contributed to the shaping of gene expression programs in different species, for adaptation to specific environments and life styles [27]. Fungi represent an excellent model system for exploring these questions. A comparative analysis in model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe showed remarkable conservation of the roles of Mediator in spite of the fact that these two yeasts are highly divergent [28]. The conserved In this study, we compared the roles of Mediator, a central transcriptional regulator in all eukaryotes, between the pathogenic fungus Candida albicans and the non-pathogenic model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. We discovered that Mediator has both shared and species-specific functions in the three yeasts. The shared functions include regulation of genes required for cell separation after cell division by the Middle domain subunit Med31. The species-specific functions include transcriptional regulation of the cell wall adhesins, which play key roles in the pathogenesis of C. albicans. In C. albicans, the Mediator subunits Med31, Med20, and Srb9/Med13 are activators of the ALS cell wall adhesins. In S. cerevisiae, our results and previous reports suggest an opposite, repressive role in the expression of the FLO genes and in adhesion-dependent phenotypes. The C. albicans Med31, Med20, and Srb9/Med13 contribute to processes highly important for disease: the switch to filamentous morphology and biofilm formation. Moreover, Med31 impacts on virulence in an invertebrate infection model. Our study has implications for understanding the regulation over virulence-associated genes in C. albicans and the roles of a key transcriptional regulator in this process. functions include a broad role in stress responses, and specific, distinct roles of the Mediator (...truncated)