Regulation of the Candida albicans Hypha-Inducing Transcription Factor Ume6 by the CDK1 Cyclins Cln3 and Hgc1

ABSTRACT The yeast to hypha (mold) morphogenetic switch of Candida albicans plays a role in its virulence and constitutes a diagnostic trait for this organism, the most prevalent systemic fungal pathogen in industrialized countries. It has long been known that hyphae are most efficiently induced from stationary cultures. Here, a molecular basis for this observation is provided. The G1 cyclin Cln3, an essential promoter of yeast proliferation, was found to suppress hyphal induction. Suppression of hyphal induction is achieved by inhibition of the activity of the central activator of hyphal morphogenesis, the transcription factor Ume6. Thus, levels of Cln3 control the switch between proliferation of C. albicans as individual yeast cells and development into extended hyphae, a switch that may preface the proliferation/differentiation switch in multicellular organisms. The ability to switch between proliferation as yeast cells and development into hyphae is a hallmark of Candida albicans. The switch to hyphal morphogenesis depends on external inducing conditions, but its efficiency is augmented in stationary-phase cells. Ume6, a transcription factor that is itself transcriptionally induced under hypha-promoting conditions, is both necessary and sufficient for hyphal morphogenesis. We found that Ume6 is regulated posttranslationally by the cell cycle kinase Cdc28/Cdk1, which reduces Ume6 activity via different mechanisms using different cyclins. Together with the cyclin Hgc1, Cdk1 promotes degradation of Ume6 via the SCFCDC4 ubiquitin ligase. Since HGC1 is a key transcriptional target of Ume6, this results in a negative-feedback loop between Hgc1 and Ume6. In addition, we found that Cln3, a G1 cyclin that is essential for cell cycle progression and yeast proliferation, suppresses hyphal morphogenesis and that Cln3 suppresses Ume6 activity both in the heterologous Saccharomyces cerevisiae system and in C. albicans itself. This activity of Cln3 may provide the basis for the antagonistic relationship between yeast proliferation and hyphal development in C. albicans. IMPORTANCE The yeast to hypha (mold) morphogenetic switch of Candida albicans plays a role in its virulence and constitutes a diagnostic trait for this organism, the most prevalent systemic fungal pathogen in industrialized countries. It has long been known that hyphae are most efficiently induced from stationary cultures. Here, a molecular basis for this observation is provided. The G1 cyclin Cln3, an essential promoter of yeast proliferation, was found to suppress hyphal induction. Suppression of hyphal induction is achieved by inhibition of the activity of the central activator of hyphal morphogenesis, the transcription factor Ume6. Thus, levels of Cln3 control the switch between proliferation of C. albicans as individual yeast cells and development into extended hyphae, a switch that may preface the proliferation/differentiation switch in multicellular organisms.

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The 5′ Untranslated Region of theEFG1Transcript Promotes Its Translation To Regulate Hyphal Morphogenesis inCandida albicans

mSphere ◽

10.1128/msphere.00280-18 ◽

2018 ◽

Vol 3 (4) ◽

Cited By ~ 2

Author(s):

Prashant R. Desai ◽

Klaus Lengeler ◽

Mario Kapitan ◽

Silas Matthias Janßen ◽

Paula Alepuz ◽

...

Keyword(s):

Candida Albicans ◽

Fungal Pathogen ◽

Untranslated Regions ◽

Regulatory Sequence ◽

Transcriptional Level ◽

Content Type ◽

Reading Frame ◽

Human Fungal Pathogen ◽

Hyphal Morphogenesis ◽

Incandida Albicans

ABSTRACTExtensive 5′ untranslated regions (UTR) are a hallmark of transcripts determining hyphal morphogenesis inCandida albicans. The major transcripts of theEFG1gene, which are responsible for cellular morphogenesis and metabolism, contain a 5′ UTR of up to 1,170 nucleotides (nt). Deletion analyses of the 5′ UTR revealed a 218-nt sequence that is required for production of the Efg1 protein and its functions in filamentation, without lowering the level and integrity of theEFG1transcript. Polysomal analyses revealed that the 218-nt 5′ UTR sequence is required for efficient translation of the Efg1 protein. Replacement of theEFG1open reading frame (ORF) by the heterologous reporter geneCaCBGlucconfirmed the positive regulatory importance of the identified 5′ UTR sequence. In contrast to other reported transcripts containing extensive 5′ UTR sequences, these results indicate the positive translational function of the 5′ UTR sequence in theEFG1transcript, which is observed in the context of the nativeEFG1promoter. It is proposed that the 5′ UTR recruits regulatory factors, possibly during emergence of the native transcript, which aid in translation of theEFG1transcript.IMPORTANCEMany of the virulence traits that makeCandida albicansan important human fungal pathogen are regulated on a transcriptional level. Here, we report an important regulatory contribution of translation, which is exerted by the extensive 5′ untranslated regulatory sequence (5′ UTR) of the transcript for the protein Efg1, which determines growth, metabolism, and filamentation in the fungus. The presence of the 5′ UTR is required for efficient translation of Efg1, to promote filamentation. Because transcripts for many relevant regulators contain extensive 5′ UTR sequences, it appears that the virulence ofC. albicansdepends on the combination of transcriptional and translational regulatory mechanisms.

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Candida albicans CUG Mistranslation Is a Mechanism To Create Cell Surface Variation

mBio ◽

10.1128/mbio.00285-13 ◽

2013 ◽

Vol 4 (4) ◽

Cited By ~ 51

Author(s):

Isabel Miranda ◽

Ana Silva-Dias ◽

Rita Rocha ◽

Rita Teixeira-Santos ◽

Carolina Coelho ◽

...

Keyword(s):

Candida Albicans ◽

Cell Surface ◽

Fungal Pathogen ◽

Single Gene ◽

Yeast Cells ◽

Phenotypic Switching ◽

Leucine Incorporation ◽

Host Immune System ◽

Content Type ◽

Human Fungal Pathogen

ABSTRACT In the human fungal pathogen Candida albicans, the CUG codon is translated 97% of the time as serine and 3% of the time as leucine, which potentially originates an array of proteins resulting from the translation of a single gene. Genes encoding cell surface proteins are enriched in CUG codons; thus, CUG mistranslation may influence the interactions of the organism with the host. To investigate this, we compared a C. albicans strain that misincorporates 28% of leucine at CUGs with a wild-type parental strain. The first strain displayed increased adherence to inert and host molecules. In addition, it was less susceptible to phagocytosis by murine macrophages, probably due to reduced exposure of cell surface β-glucans. To prove that these phenotypes occurred due to serine/leucine exchange, the C. albicans adhesin and invasin ALS3 was expressed in Saccharomyces cerevisiae in its two natural isoforms (Als3p-Leu and Als3p-Ser). The cells with heterologous expression of Als3p-Leu showed increased adherence to host substrates and flocculation. We propose that CUG mistranslation has been maintained during the evolution of C. albicans due to its potential to generate cell surface variability, which significantly alters fungus-host interactions. IMPORTANCE The translation of genetic information into proteins is a highly accurate cellular process. In the human fungal pathogen Candida albicans, a unique mistranslation event involving the CUG codon occurs. The CUG codon is mainly translated as serine but can also be translated as leucine. Leucine and serine are two biochemically distinct amino acids, hydrophobic and hydrophilic, respectively. The increased rate of leucine incorporation at CUG decoding triggers C. albicans virulence attributes, such as morphogenesis, phenotypic switching, and adhesion. Here, we show that CUG mistranslation masks the fungal cell wall molecule β-glucan that is normally recognized by the host immune system, delaying its response. Furthermore, we demonstrate that two different proteins of the adhesin Als3 generated by CUG mistranslation confer increased hydrophobicity and adhesion ability on yeast cells. Thus, CUG mistranslation functions as a mechanism to create protein diversity with differential activities, constituting an advantage for a mainly asexual microorganism. This could explain its preservation during evolution.

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G 1 /S Transcription Factor Orthologues Swi4p and Swi6p Are Important but Not Essential for Cell Proliferation and Influence Hyphal Development in the Fungal Pathogen Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00278-10 ◽

2011 ◽

Vol 10 (3) ◽

pp. 384-397 ◽

Cited By ~ 17

Author(s):

Bahira Hussein ◽

Hao Huang ◽

Amandeep Glory ◽

Amin Osmani ◽

Susan Kaminskyj ◽

...

Keyword(s):

Cell Proliferation ◽

Candida Albicans ◽

Fungal Pathogen ◽

Expression Patterns ◽

Control Point ◽

Yeast Cells ◽

Content Type ◽

Hyphal Development ◽

Critical Control Point ◽

Transcription Profiles

ABSTRACT The G 1 /S transition is a critical control point for cell proliferation and involves essential transcription complexes termed SBF and MBF in Saccharomyces cerevisiae or MBF in Schizosaccharomyces pombe . In the fungal pathogen Candida albicans , G 1 /S regulation is not clear. To gain more insight into the G 1 /S circuitry, we characterized Swi6p, Swi4p and Mbp1p, the closest orthologues of SBF (Swi6p and Swi4p) and MBF (Swi6p and Mbp1p) components in S. cerevisiae . The mbp1 Δ/Δ cells showed minor growth defects, whereas swi4 Δ/Δ and swi6 Δ/Δ yeast cells dramatically increased in size, suggesting a G 1 phase delay. G ene s et e nrichment a nalysis (GSEA) of transcription profiles revealed that genes associated with G 1 /S phase were significantly enriched in cells lacking Swi4p and Swi6p. These expression patterns suggested that Swi4p and Swi6p have repressing as well as activating activity. Intriguingly, swi4 Δ / Δ swi6 Δ/Δ and swi4 Δ / Δ mbp1 Δ/Δ strains were viable, in contrast to the situation in S. cerevisiae , and showed pleiotropic phenotypes that included multibudded yeast, pseudohyphae, and intriguingly, true hyphae. Consistently, GSEA identified strong enrichment of genes that are normally modulated during C. albicans -host cell interactions. Since Swi4p and Swi6p influence G 1 phase progression and SBF binding sites are lacking in the C. albicans genome, these factors may contribute to MBF activity. Overall, the data suggest that the putative G 1 /S regulatory machinery of C. albican s contains novel features and underscore the existence of a relationship between G 1 phase and morphogenetic switching, including hyphal development, in the pathogen.

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Phagosomal Neutralization by the Fungal Pathogen Candida albicans Induces Macrophage Pyroptosis

Infection and Immunity ◽

10.1128/iai.00832-16 ◽

2016 ◽

Vol 85 (2) ◽

Cited By ~ 36

Author(s):

Slavena Vylkova ◽

Michael C. Lorenz

Keyword(s):

Amino Acids ◽

Transcription Factor ◽

Candida Albicans ◽

Amino Acid ◽

Content Type ◽

Caspase 1 ◽

Ammonia Release ◽

Hyphal Morphogenesis

ABSTRACT The interaction of Candida albicans with the innate immune system is the key determinant of the pathogen/commensal balance and has selected for adaptations that facilitate the utilization of nutrients commonly found within the host, including proteins and amino acids; many of the catabolic pathways needed to assimilate these compounds are required for persistence in the host. We have shown that C. albicans co-opts amino acid catabolism to generate and excrete ammonia, which raises the extracellular pH, both in vitro and in vivo and induces hyphal morphogenesis. Mutants defective in the uptake or utilization of amino acids, such as those lacking STP2, a transcription factor that regulates the expression of amino acid permeases, are impaired in multiple aspects of fungus-macrophage interactions resulting from an inability to neutralize the phagosome. Here we identified a novel role in amino acid utilization for Ahr1p, a transcription factor previously implicated in regulation of adherence and hyphal morphogenesis. Mutants lacking AHR1 were defective in growth, alkalinization, and ammonia release on amino acid-rich media, similar to stp2Δ and ahr1Δ stp2Δ cells, and occupied more acidic phagosomes. Notably, ahr1Δ and stp2Δ strains did not induce pyroptosis, as measured by caspase-1-dependent interleukin-1β release, though this phenotype could be suppressed by pharmacological neutralization of the phagosome. Altogether, we show that C. albicans-driven neutralization of the phagosome promotes hyphal morphogenesis, sufficient for induction of caspase-1-mediated macrophage lysis.

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Orthologues of the Anaphase-Promoting Complex/Cyclosome Coactivators Cdc20p and Cdh1p Are Important for Mitotic Progression and Morphogenesis in Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00263-10 ◽

2011 ◽

Vol 10 (5) ◽

pp. 696-709 ◽

Cited By ~ 13

Author(s):

Hsini Chou ◽

Amandeep Glory ◽

Catherine Bachewich

Keyword(s):

Candida Albicans ◽

Fungal Pathogen ◽

Regulatory Networks ◽

Yeast Cells ◽

Anaphase Promoting Complex ◽

Mitotic Progression ◽

Content Type ◽

Mitotic Cyclin ◽

Late Mitosis ◽

A Minor

ABSTRACTThe conserved anaphase-promoting complex/cyclosome (APC/C) system mediates protein degradation during mitotic progression. Conserved coactivators Cdc20p and Cdh1p regulate the APC/C during early to late mitosis and G1phase.Candida albicansis an important fungal pathogen of humans, and it forms highly polarized cells when mitosis is blocked through depletion of the polo-like kinase Cdc5p or other treatments. However, the mechanisms governing mitotic progression and associated polarized growth in the pathogen are poorly understood. In order to gain insights into these processes, we characterizedC. albicansorthologues of Cdc20p and Cdh1p. Cdc20p-depleted cells were blocked in early or late mitosis with elevated levels of Cdc5p and the mitotic cyclin Clb2p, suggesting that Cdc20p is essential and has some conserved functions during mitosis. However, the yeast cells formed highly polarized buds in contrast to the large doublets ofS. cerevisiaecdc20mutants, implying a distinct role in morphogenesis. In comparison,cdh1Δ/cdh1Δcells were viable but showed enrichment of Clb2p and Cdc5p, suggesting that Cdh1p may influence mitotic exit. Thecdh1Δ/cdh1Δphenotype was pleiotropic, consisting of normal or enlarged yeast, pseudohyphae, and some elongated buds, whereasS. cerevisiaecdh1Δyeast cells were reduced in size. Thus,C. albicansCdh1p may have some distinct functions. Finally, absence of Cdh1p or Cdc20p had a minor or no effect on hyphal development, respectively. Overall, the results suggest that Cdc20p and Cdh1p may be APC/C activators that are important for mitosis but also morphogenesis inC. albicans. Their novel features imply additional variations in function and underscore rewiring in the emerging mitotic regulatory networks of the pathogen.

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Functional Mapping of Transcription Factor Grf10 That Regulates Adenine-Responsive and Filamentation Genes inCandida albicans

mSphere ◽

10.1128/msphere.00467-18 ◽

2018 ◽

Vol 3 (5) ◽

Cited By ~ 1

Author(s):

Tanaporn Wangsanut ◽

Joshua M. Tobin ◽

Ronda J. Rolfes

Keyword(s):

Transcription Factor ◽

Candida Albicans ◽

Transcription Factors ◽

Carbon Metabolism ◽

Fungal Pathogen ◽

Functional Domains ◽

Content Type ◽

Activation Domains ◽

Human Fungal Pathogen ◽

One Carbon Metabolism

ABSTRACTGrf10, a homeodomain-containing transcription factor, regulates adenylate and one-carbon metabolism and morphogenesis in the human fungal pathogenCandida albicans. Here, we identified functional domains and key residues involved in transcription factor activity using one-hybrid and mutational analyses. We localized activation domains to the C-terminal half of the Grf10 protein by one-hybrid analysis and identified motifs using bioinformatic analyses; one of the characterized activation domains (AD1) responded to temperature. The LexA-Grf10 fusion protein activated thelexAop-HIS1reporter in an adenine-dependent fashion, and this activation was independent of Bas1, showing that the adenine limitation signal is transmitted directly to Grf10. Overexpression of LexA-Grf10 led to filamentation, and this required a functioning homeodomain, consistent with Grf10 controlling the expression of key filamentation genes; filamentation induced by LexA-Grf10 overexpression was independent of adenine levels and Bas1. Alanine substitutions were made within the conserved interaction regions (IR) of LexA-Grf10 and Grf10 to investigate roles in transcription. In LexA-Grf10, the D302A mutation activated transcription constitutively, and the E305A mutation was regulated by adenine. When these mutations were introduced into the native gene locus, the D302A mutation was unable to complement the ADE phenotype and did not promote filamentation under hypha-inducing conditions; the E305A mutant behaved as the native gene with respect to the ADE phenotype and was partially defective in inducing hyphae. These results demonstrate allele-specific responses with respect to the different phenotypes, consistent with perturbations in the ability of Grf10 to interact with multiple partner proteins.IMPORTANCEMetabolic adaptation and morphogenesis are essential forCandida albicans, a major human fungal pathogen, to survive and infect diverse body sites in the mammalian host.C. albicansutilizes transcription factors to tightly control the transcription of metabolic genes and morphogenesis genes. Grf10, a critical homeodomain transcription factor, controls purine and one-carbon metabolism in response to adenine limitation, and Grf10 is necessary for the yeast-to-hypha morphological switching, a known virulence factor. Here, we carried out one-hybrid and mutational analyses to identify functional domains of Grf10. Our results show that Grf10 separately regulates metabolic and morphogenesis genes, and it contains a conserved protein domain for protein partner interaction, allowing Grf10 to control the transcription of multiple distinct pathways. Our findings contribute significantly to understanding the role and mechanism of transcription factors that control multiple pathogenic traits inC. albicans.

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DeORFanizing Candida albicans Genes using Coexpression

mSphere ◽

10.1128/msphere.01245-20 ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Teresa R. O’Meara ◽

Matthew J. O’Meara

Keyword(s):

Cell Cycle ◽

Candida Albicans ◽

Gene Function ◽

Fungal Pathogen ◽

Large Scale ◽

Open Reading Frames ◽

Coexpression Network ◽

Content Type ◽

Reading Frames

ABSTRACT Functional characterization of open reading frames in nonmodel organisms, such as the common opportunistic fungal pathogen Candida albicans, can be labor-intensive. To meet this challenge, we built a comprehensive and unbiased coexpression network for C. albicans, which we call CalCEN, from data collected from 853 RNA sequencing runs from 18 large-scale studies deposited in the NCBI Sequence Read Archive. Retrospectively, CalCEN is highly predictive of known gene function annotations and can be synergistically combined with sequence similarity and interaction networks in Saccharomyces cerevisiae through orthology for additional accuracy in gene function prediction. To prospectively demonstrate the utility of the coexpression network in C. albicans, we predicted the function of underannotated open reading frames (ORFs) and identified CCJ1 as a novel cell cycle regulator in C. albicans. This study provides a tool for future systems biology analyses of gene function in C. albicans. We provide a computational pipeline for building and analyzing the coexpression network and CalCEN itself at http://github.com/momeara/CalCEN. IMPORTANCE Candida albicans is a common and deadly fungal pathogen of humans, yet the genome of this organism contains many genes of unknown function. By determining gene function, we can help identify essential genes, new virulence factors, or new regulators of drug resistance, and thereby give new targets for antifungal development. Here, we use information from large-scale RNA sequencing (RNAseq) studies and generate a C. albicans coexpression network (CalCEN) that is robust and able to predict gene function. We demonstrate the utility of this network in both retrospective and prospective testing and use CalCEN to predict a role for C4_06590W/CCJ1 in cell cycle. This tool will allow for a better characterization of underannotated genes in pathogenic yeasts.

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An Efficient, Rapid, and Recyclable System for CRISPR-Mediated Genome Editing in Candida albicans

mSphere ◽

10.1128/mspheredirect.00149-17 ◽

2017 ◽

Vol 2 (2) ◽

Cited By ~ 33

Author(s):

Namkha Nguyen ◽

Morgan M. F. Quail ◽

Aaron D. Hernday

Keyword(s):

Candida Albicans ◽

Genome Editing ◽

Fungal Pathogen ◽

Gene Knockout ◽

Strain Engineering ◽

Molecular Genetic Analysis ◽

Content Type ◽

Highly Efficient ◽

Discovery Research ◽

Gene Knockouts

ABSTRACT Candida albicans is the most common fungal pathogen of humans. Historically, molecular genetic analysis of this important pathogen has been hampered by the lack of stable plasmids or meiotic cell division, limited selectable markers, and inefficient methods for generating gene knockouts. The recent development of clustered regularly interspaced short palindromic repeat(s) (CRISPR)-based tools for use with C. albicans has opened the door to more efficient genome editing; however, previously reported systems have specific limitations. We report the development of an optimized CRISPR-based genome editing system for use with C. albicans. Our system is highly efficient, does not require molecular cloning, does not leave permanent markers in the genome, and supports rapid, precise genome editing in C. albicans. We also demonstrate the utility of our system for generating two independent homozygous gene knockouts in a single transformation and present a method for generating homozygous wild-type gene addbacks at the native locus. Furthermore, each step of our protocol is compatible with high-throughput strain engineering approaches, thus opening the door to the generation of a complete C. albicans gene knockout library. IMPORTANCE Candida albicans is the major fungal pathogen of humans and is the subject of intense biomedical and discovery research. Until recently, the pace of research in this field has been hampered by the lack of efficient methods for genome editing. We report the development of a highly efficient and flexible genome editing system for use with C. albicans. This system improves upon previously published C. albicans CRISPR systems and enables rapid, precise genome editing without the use of permanent markers. This new tool kit promises to expedite the pace of research on this important fungal pathogen.

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Regulation of Yeast-to-Hyphae Transition inYarrowia lipolytica

mSphere ◽

10.1128/msphere.00541-18 ◽

2018 ◽

Vol 3 (6) ◽

Cited By ~ 9

Author(s):

Kyle R. Pomraning ◽

Erin L. Bredeweg ◽

Eduard J. Kerkhoven ◽

Kerrie Barry ◽

Sajeet Haridas ◽

...

Keyword(s):

Cell Cycle ◽

Transcription Factor ◽

Stress Response ◽

Hyphal Growth ◽

Genetic Screen ◽

Morphological Transition ◽

Histidine Kinases ◽

Content Type ◽

Forward Genetic Screen ◽

Response To Stress

ABSTRACTThe yeastYarrowia lipolyticaundergoes a morphological transition from yeast-to-hyphal growth in response to environmental conditions. A forward genetic screen was used to identify mutants that reliably remain in the yeast phase, which were then assessed by whole-genome sequencing. All thesmoothmutants identified, so named because of their colony morphology, exhibit independent loss of DNA at a repetitive locus made up of interspersed ribosomal DNA and short 10- to 40-mer telomere-like repeats. The loss of repetitive DNA is associated with downregulation of genes with stress response elements (5′-CCCCT-3′) and upregulation of genes with cell cycle box (5′-ACGCG-3′) motifs in their promoter region. The stress response element is bound by the transcription factor Msn2p inSaccharomyces cerevisiae. We confirmed that theY. lipolyticamsn2(Ylmsn2) ortholog is required for hyphal growth and found that overexpression of Ylmsn2enables hyphal growth insmoothstrains. The cell cycle box is bound by the Mbp1p/Swi6p complex inS. cerevisiaeto regulate G1-to-S phase progression. We found that overexpression of either the Ylmbp1or Ylswi6homologs decreased hyphal growth and that deletion of either Ylmbp1or Ylswi6promotes hyphal growth insmoothstrains. A second forward genetic screen for reversion to hyphal growth was performed with thesmooth-33mutant to identify additional genetic factors regulating hyphal growth inY. lipolytica. Thirteen of the mutants sequenced from this screen had coding mutations in five kinases, including the histidine kinases Ylchk1and Ylnik1and kinases of the high-osmolarity glycerol response (HOG) mitogen-activated protein (MAP) kinase cascade Ylssk2, Ylpbs2, and Ylhog1. Together, these results demonstrate thatY. lipolyticatransitions to hyphal growth in response to stress through multiple signaling pathways.IMPORTANCEMany yeasts undergo a morphological transition from yeast-to-hyphal growth in response to environmental conditions. We used forward and reverse genetic techniques to identify genes regulating this transition inYarrowia lipolytica. We confirmed that the transcription factor Ylmsn2is required for the transition to hyphal growth and found that signaling by the histidine kinases Ylchk1and Ylnik1as well as the MAP kinases of the HOG pathway (Ylssk2, Ylpbs2, and Ylhog1) regulates the transition to hyphal growth. These results suggest thatY. lipolyticatransitions to hyphal growth in response to stress through multiple kinase pathways. Intriguingly, we found that a repetitive portion of the genome containing telomere-like and rDNA repeats may be involved in the transition to hyphal growth, suggesting a link between this region and the general stress response.

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The 5’ untranslated region of theEFG1transcript promotes its translation to regulate hyphal morphogenesis inCandida albicans

10.1101/328948 ◽

2018 ◽

Author(s):

Prashant R. Desai ◽

Klaus Lengeler ◽

Mario Kapitan ◽

Silas Matthias Janßen ◽

Paula Alepuz ◽

...

Keyword(s):

Candida Albicans ◽

Fungal Pathogen ◽

Regulatory Mechanisms ◽

Untranslated Regions ◽

Regulatory Sequence ◽

Transcriptional Level ◽

Human Fungal Pathogen ◽

Hyphal Morphogenesis ◽

Cellular Morphogenesis ◽

Incandida Albicans

ABSTRACTExtensive 5’ untranslated regions (UTR) are a hallmark of transcripts determining hyphal morphogenesis inCandida albicans.The major transcripts of theEFG1gene, which are responsible for cellular morphogenesis and metabolism, contain a 5’ UTR of up to 1170 nt. Deletion analyses of the 5’ UTR revealed a 218 nt sequence that is required for production of the Efg1 protein and its functions in filamentation, without lowering the level and integrity of theEFG1transcript. Polysomal analyses revealed that the 218 nt 5’ UTR sequence is required for efficient translation of the Efg1 protein. Replacement of theEFG1ORF by the heterologous reporter geneCaCBGlucconfirmed the positive regulatory importance of the identified 5’ UTR sequence. In contrast to other reported transcripts containing extensive 5’ UTR sequences, these results indicate the positive translational function of the 5’ UTR sequence in theEFG1transcript, which is observed in context of the nativeEFG1promoter. The results suggest that the 5’ UTR recruits regulatory factors, possibly during emergence of the native transcript, which aid in translation of theEFG1transcript.IMPORTANCEMany of the virulence traits that makeCandida albicansan important human fungal pathogen are regulated on a transcriptional level. Here we report an important regulatory contribution of translation, which is exerted by the extensive 5’ untranslated regulatory sequence (5’ UTR) of the transcript for the protein Efg1, which determines growth, metabolism and filamentation in the fungus. Presence of the 5’ UTR is required for efficient translation of Efg1, to promote filamentation. Because transcripts for many relevant regulators contain extensive 5’ UTR sequences, it appears that virulence ofC. albicansdepends on the combination of transcriptional and translation regulatory mechanisms.

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