title: Amplification of TLO Mediator Subunit Genes Facilitate Filamentous Growth in Candida Spp.
abstract: Filamentous growth is a hallmark of C. albicans pathogenicity compared to less-virulent ascomycetes. A multitude of transcription factors regulate filamentous growth in response to specific environmental cues. Our work, however, suggests the evolutionary history of C. albicans that resulted in its filamentous growth plasticity may be tied to a change in the general transcription machinery rather than transcription factors and their specific targets. A key genomic difference between C. albicans and its less-virulent relatives, including its closest relative C. dubliniensis, is the unique expansion of the TLO (TeLOmere-associated) gene family in C. albicans. Individual Tlo proteins are fungal-specific subunits of Mediator, a large multi-subunit eukaryotic transcriptional co-activator complex. This amplification results in a large pool of 'free,' non-Mediator associated, Tlo protein present in C. albicans, but not in C. dubliniensis or other ascomycetes with attenuated virulence. We show that engineering a large 'free' pool of the C. dubliniensis Tlo2 (CdTlo2) protein in C. dubliniensis, through overexpression, results in a number of filamentation phenotypes typically associated only with C. albicans. The amplitude of these phenotypes is proportional to the amount of overexpressed CdTlo2 protein. Overexpression of other C. dubliniensis and C. albicans Tlo proteins do result in these phenotypes. Tlo proteins and their orthologs contain a Mediator interaction domain, and a potent transcriptional activation domain. Nuclear localization of the CdTlo2 activation domain, facilitated naturally by the Tlo Mediator binding domain or artificially through an appended nuclear localization signal, is sufficient for the CdTlo2 overexpression phenotypes. A C. albicans med3 null mutant causes multiple defects including the inability to localize Tlo proteins to the nucleus and reduced virulence in a murine systemic infection model. Our data supports a model in which the activation domain of 'free' Tlo protein competes with DNA bound transcription factors for targets that regulate key aspects of C. albicans cell physiology.
authors.affiliation: Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Zhongle
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Microbiology Research Unit, Division of Oral Biosciences, Dublin Dental University Hospital, University of Dublin, Dublin, Ireland.
authors.forename: Gary P
authors.initials: GP
authors.lastname: Moran
authors.affiliation: Microbiology Research Unit, Division of Oral Biosciences, Dublin Dental University Hospital, University of Dublin, Dublin, Ireland.
authors.forename: Derek J
authors.identifier: http://orcid.org/0000-0003-0195-9697
authors.initials: DJ
authors.lastname: Sullivan
authors.affiliation: Aberdeen Fungal Group, School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Donna M
authors.identifier: http://orcid.org/0000-0003-4833-0378
authors.initials: DM
authors.lastname: MacCallum
authors.affiliation: Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.|Department of Medical Education, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Lawrence C
authors.initials: LC
authors.lastname: Myers
mesh_terms: D000818:Animals; D002176:Candida albicans / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D002177:Candidiasis / Q000235:genetics* / Q000382:microbiology / Q000473:pathology; D005658:Fungi / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity; D015966:Gene Expression Regulation, Fungal; D023281:Genomics; D006801:Humans; D025301:Hyphae / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity; D051379:Mice; D010641:Phenotype; D016615:Telomere / Q000235:genetics*; D034501:Telomere-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D034501:Telomere-Binding Proteins