Phytosphingosine-1-Phosphate Is a Signaling Molecule Involved in Miconazole Resistance in Sessile Candida albicans Cells

ABSTRACTPrevious research has shown that 1% to 10% of sessileCandida albicanscells survive treatment with high doses of miconazole (a fungicidal imidazole). In the present study, we investigated the involvement of sphingolipid biosynthetic intermediates in this survival. We observed that theLCB4gene, coding for the enzyme that catalyzes the phosphorylation of dihydrosphingosine and phytosphingosine, is important in governing the miconazole resistance of sessileSaccharomyces cerevisiaeandC. albicanscells. The addition of 10 nM phytosphingosine-1-phosphate (PHS-1-P) drastically reduced the intracellular miconazole concentration and significantly increased the miconazole resistance of a hypersusceptibleC. albicansheterozygousLCB4/lcb4mutant, indicating a protective effect of PHS-1-P against miconazole-induced cell death in sessile cells. At this concentration of PHS-1-P, we did not observe any effect on the fluidity of the cytoplasmic membrane. The protective effect of PHS-1-P was not observed when the efflux pumps were inhibited or when tested in a mutant without functional efflux systems. Also, the addition of PHS-1-P during miconazole treatment increased the expression levels of genes coding for efflux pumps, leading to the hypothesis that PHS-1-P acts as a signaling molecule and enhances the efflux of miconazole in sessileC. albicanscells.

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Impact of a Cross-Kingdom Signaling Molecule of Candida albicans on Acinetobacter baumannii Physiology

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01540-15 ◽

2015 ◽

Vol 60 (1) ◽

pp. 161-167 ◽

Cited By ~ 19

Author(s):

Xenia Kostoulias ◽

Gerald L. Murray ◽

Gustavo M. Cerqueira ◽

Jason B. Kong ◽

Farkad Bantun ◽

...

Keyword(s):

Candida Albicans ◽

Cell Membrane ◽

Acinetobacter Baumannii ◽

Biofilm Formation ◽

Defense Mechanism ◽

Membrane Integrity ◽

Efflux Pumps ◽

Signaling Molecule ◽

Content Type ◽

Antagonistic Interactions

ABSTRACTMultidrug-resistant (MDR)Acinetobacter baumanniiis an opportunistic human pathogen that has become highly problematic in the clinical environment. Novel therapies are desperately required. To assist in identifying new therapeutic targets, the antagonistic interactions betweenA. baumanniiand the most common human fungal pathogen,Candida albicans, were studied. We have observed that theC. albicansquorum-sensing molecule, farnesol, has cross-kingdom interactions, affecting the viability ofA. baumannii. To gain an understanding of its mechanism, the transcriptional profile ofA. baumanniiexposed to farnesol was examined. Farnesol caused dysregulation of a large number of genes involved in cell membrane biogenesis, multidrug efflux pumps (AcrAB-like and AdeIJK-like), andA. baumanniivirulence traits such as biofilm formation (csuA,csuB, andompA) and motility (pilZandpilH). We also observed a strong induction in genes involved in cell division (minD,minE,ftsK,ftsB, andftsL). These transcriptional data were supported by functional assays showing that farnesol disruptsA. baumanniicell membrane integrity, alters cell morphology, and impairs virulence characteristics such as biofilm formation and twitching motility. Moreover, we showed thatA. baumanniiuses efflux pumps as a defense mechanism against this eukaryotic signaling molecule. Owing to its effects on membrane integrity, farnesol was tested to see if it potentiated the activity of the membrane-acting polymyxin antibiotic colistin. When coadministered, farnesol increased sensitivity to colistin for otherwise resistant strains. These data provide mechanistic understanding of the antagonistic interactions between diverse pathogens and may provide important insights into novel therapeutic strategies.

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Nanoscale Effects of Caspofungin against Two Yeast Species, Saccharomyces cerevisiae and Candida albicans

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00105-13 ◽

2013 ◽

Vol 57 (8) ◽

pp. 3498-3506 ◽

Cited By ~ 43

Author(s):

C. Formosa ◽

M. Schiavone ◽

H. Martin-Yken ◽

J. M. François ◽

R. E. Duval ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Cell Wall ◽

Candida Albicans ◽

Yeast Species ◽

Young Modulus ◽

Antifungal Drugs ◽

Molecular Organization ◽

Response To Treatment ◽

Content Type ◽

High Doses

ABSTRACTSaccharomyces cerevisiaeandCandida albicansare model yeasts for biotechnology and human health, respectively. We used atomic force microscopy (AFM) to explore the effects of caspofungin, an antifungal drug used in hospitals, on these two species. Our nanoscale investigation revealed similar, but also different, behaviors of the two yeasts in response to treatment with the drug. While administration of caspofungin induced deep cell wall remodeling in both yeast species, as evidenced by a dramatic increase in chitin and decrease in β-glucan content, changes in cell wall composition were more pronounced withC. albicanscells. Notably, the increase of chitin was proportional to the increase in the caspofungin dose. In addition, the Young modulus of the cell was three times lower forC. albicanscells than forS. cerevisiaecells and increased proportionally with the increase of chitin, suggesting differences in the molecular organization of the cell wall between the two yeast species. Also, at a low dose of caspofungin (i.e., 0.5× MIC), the cell surface ofC. albicansexhibited a morphology that was reminiscent of cells expressing adhesion proteins. Interestingly, this morphology was lost at high doses of the drug (i.e., 4× MIC). However, the treatment ofS. cerevisiaecells with high doses of caspofungin resulted in impairment of cytokinesis. Altogether, the use of AFM for investigating the effects of antifungal drugs is relevant in nanomedicine, as it should help in understanding their mechanisms of action on fungal cells, as well as unraveling unexpected effects on cell division and fungal adhesion.

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Cell Wall-Related Bionumbers and Bioestimates of Saccharomyces cerevisiae and Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00250-13 ◽

2013 ◽

Vol 13 (1) ◽

pp. 2-9 ◽

Cited By ~ 58

Author(s):

Frans M. Klis ◽

Chris G. de Koster ◽

Stanley Brul

Keyword(s):

Saccharomyces Cerevisiae ◽

Cell Wall ◽

Candida Albicans ◽

Cell Size ◽

Pathogenic Fungus ◽

Turgor Pressure ◽

Hyphal Growth ◽

Biological Research ◽

Content Type ◽

Starting Point

ABSTRACTBionumbers and bioestimates are valuable tools in biological research. Here we focus on cell wall-related bionumbers and bioestimates of the budding yeastSaccharomyces cerevisiaeand the polymorphic, pathogenic fungusCandida albicans. We discuss the linear relationship between cell size and cell ploidy, the correlation between cell size and specific growth rate, the effect of turgor pressure on cell size, and the reason why using fixed cells for measuring cellular dimensions can result in serious underestimation ofin vivovalues. We further consider the evidence that individual buds and hyphae grow linearly and that exponential growth of the population results from regular formation of new daughter cells and regular hyphal branching. Our calculations show that hyphal growth allowsC. albicansto cover much larger distances per unit of time than the yeast mode of growth and that this is accompanied by strongly increased surface expansion rates. We therefore predict that the transcript levels of genes involved in wall formation increase during hyphal growth. Interestingly, wall proteins and polysaccharides seem barely, if at all, subject to turnover and replacement. A general lesson is how strongly most bionumbers and bioestimates depend on environmental conditions and genetic background, thus reemphasizing the importance of well-defined and carefully chosen culture conditions and experimental approaches. Finally, we propose that the numbers and estimates described here offer a solid starting point for similar studies of other cell compartments and other yeast species.

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A Combination Fluorescence Assay Demonstrates Increased Efflux Pump Activity as a Resistance Mechanism in Azole-Resistant Vaginal Candida albicans Isolates

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01252-16 ◽

2016 ◽

Vol 60 (10) ◽

pp. 5858-5866 ◽

Cited By ~ 23

Author(s):

Somanon Bhattacharya ◽

Jack D. Sobel ◽

Theodore C. White

Keyword(s):

Candida Albicans ◽

Efflux Pump ◽

Pathogenic Fungus ◽

Resistance Mechanism ◽

Efflux Pumps ◽

Resistant Isolate ◽

Vaginal Infections ◽

Content Type ◽

Qrt Pcr ◽

Pump Activity

ABSTRACTCandida albicansis a pathogenic fungus causing vulvovaginal candidiasis (VVC). Azole drugs, such as fluconazole, are the most common treatment for these infections. Recently, azole-resistant vaginalC. albicansisolates have been detected in patients with recurring and refractory vaginal infections. However, the mechanisms of resistance in vaginalC. albicansisolates have not been studied in detail. In oral and systemic resistant isolates, overexpression of the ABC transporters Cdr1p and Cdr2p and the major facilitator transporter Mdr1p is associated with resistance. Sixteen fluconazole-susceptible and 22 fluconazole-resistant vaginalC. albicansisolates were obtained, including six matched sets containing a susceptible and a resistant isolate, from individual patients. Using quantitative real-time reverse transcriptase PCR (qRT-PCR), 16 of 22 resistant isolates showed overexpression of at least one efflux pump gene, while only 1 of 16 susceptible isolates showed such overexpression. To evaluate the pump activity associated with overexpression, an assay that combined data from two separate fluorescent assays using rhodamine 6G and alanine β-naphthylamide was developed. The qRT-PCR results and activity assay results were in good agreement. This combination of two fluorescent assays can be used to study efflux pumps as resistance mechanisms in clinical isolates. These results demonstrate that efflux pumps are a significant resistance mechanism in vaginalC. albicansisolates.

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The “Finger,” a Unique Multicellular Morphology of Candida albicans Induced by CO2and Dependent upon the Ras1-Cyclic AMP Pathway

Eukaryotic Cell ◽

10.1128/ec.00217-12 ◽

2012 ◽

Vol 11 (10) ◽

pp. 1257-1267 ◽

Cited By ~ 7

Author(s):

Karla J. Daniels ◽

Claude Pujol ◽

Thyagarajan Srikantha ◽

David R. Soll

Keyword(s):

Candida Albicans ◽

Cyclic Amp ◽

Mutational Analysis ◽

Cell Monolayer ◽

Yeast Cells ◽

Content Type ◽

Dispersal Mechanism ◽

Basal Bulb ◽

High Doses

ABSTRACTMost experiments exploring the basic biology of pathogenic microbes are performedin vitrounder conditions that do not usually mimic those of their host niche. Hence, developmental programs initiated by specific host cues may be missedin vitro. We have tested the effects of growing low-density agar cultures of the yeast pathogenCandida albicansin concentrations of CO2found in the gastrointestinal tract. It is demonstrated that in physiological concentrations of CO2at 37°C, yeast cells form a heretofore undescribed multicellular “finger” morphology distinct from a previously described stalk-like structure induced by high doses of UV irradiation that kills more than 99.99% of cells. The finger extends aerially, is uniform in diameter, and is visible to the naked eye, attaining lengths of 3 mm. It is composed of a basal yeast cell monolayer adhering to a semispherical crater formed in the agar and connected to a basal bulb of yeast cells at a fragile interface. The bulb extends into the long shaft. We propose that a single, centrally located hypha extending the length of the shaft forms buds at compartment junctions that serve as the source of the yeast cells in the shaft. A mutational analysis reveals finger formation is dependent upon the pathway Ras1→Cdc35→cyclic AMP (cAMP) (PDE2—|)→Tpk2→Tec1. Because of the mechanically fragile interface and the compactness of bulb and shaft, we suggest that the finger may function as a multicellular dispersal mechanism produced in host niches containing high levels of CO2.

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Put3 Positively Regulates Proline Utilization in Candida albicans

mSphere ◽

10.1128/msphere.00354-17 ◽

2017 ◽

Vol 2 (6) ◽

Cited By ~ 9

Author(s):

Walters Aji Tebung ◽

Raha Parvizi Omran ◽

Debra L. Fulton ◽

Joachim Morschhäuser ◽

Malcolm Whiteway

Keyword(s):

Saccharomyces Cerevisiae ◽

Transcription Factor ◽

Candida Albicans ◽

Nitrogen Source ◽

Opportunistic Pathogen ◽

Baker's Yeast ◽

Null Mutant ◽

Multiple Sources ◽

Content Type ◽

Proline Catabolism

ABSTRACT Candida albicans poses a significant threat to the lives of immunocompromised people. Historically, knowledge has been drawn from studies on Saccharomyces cerevisiae to understand the pathogen, and many Candida albicans genes are named after their S. cerevisiae orthologs. Direct studies on the pathogen have, however, revealed differences in the roles of some orthologous proteins in the two yeasts. We show that the Put3 transcription factor allows the pathogen to completely degrade proline to usable nitrogen and carbon by evading regulatory restrictions imposed on its S. cerevisiae ortholog, which mandates conditional use of proline only as a nitrogen source in the baker’s yeast. The ability of Candida albicans to freely obtain nutrients from multiple sources may help it thrive as a commensal and opportunistic pathogen. The zinc cluster transcription factor Put3 was initially characterized in Saccharomyces cerevisiae as the transcriptional activator of PUT1 and PUT2, two genes acting early in the proline assimilation pathway. We have used phenotypic studies, transcription profiling, and chromatin immunoprecipitation with microarray technology (ChIP-chip) to establish that unlike S. cerevisiae, which only uses proline as a nitrogen source, Candida albicans can use proline as a nitrogen source, a carbon source, or a source of both nitrogen and carbon. However, a C. albicans put3 null mutant cannot grow on proline, suggesting that as in S. cerevisiae, C. albicans Put3 (CaPut3) is required for proline catabolism, and because the C. albicans put3 null mutant grew efficiently on glutamate as the sole carbon or nitrogen source, it appears that CaPut3 also regulates the early genes of the pathway. CaPut3 showed direct binding to the CaPUT1 promoter, and both PUT1 and PUT2 were upregulated in response to proline addition in a Put3-dependent manner, as well as in a C. albicans strain expressing a hyperactive Put3. CaPut3 directs proline degradation even in the presence of a good nitrogen source such as ammonia, which contrasts with S. cerevisiae Put3 (ScPut3)-regulated proline catabolism, which only occurs in the absence of a rich nitrogen source. Thus, while overall proline regulatory circuitry differs between S. cerevisiae and C. albicans, the specific role of Put3 appears fundamentally conserved. IMPORTANCE Candida albicans poses a significant threat to the lives of immunocompromised people. Historically, knowledge has been drawn from studies on Saccharomyces cerevisiae to understand the pathogen, and many Candida albicans genes are named after their S. cerevisiae orthologs. Direct studies on the pathogen have, however, revealed differences in the roles of some orthologous proteins in the two yeasts. We show that the Put3 transcription factor allows the pathogen to completely degrade proline to usable nitrogen and carbon by evading regulatory restrictions imposed on its S. cerevisiae ortholog, which mandates conditional use of proline only as a nitrogen source in the baker’s yeast. The ability of Candida albicans to freely obtain nutrients from multiple sources may help it thrive as a commensal and opportunistic pathogen.

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Utilization of the Mating Scaffold Protein in the Evolution of a New Signal Transduction Pathway for Biofilm Development

mBio ◽

10.1128/mbio.00237-10 ◽

2011 ◽

Vol 2 (1) ◽

Cited By ~ 17

Author(s):

Song Yi ◽

Nidhi Sahni ◽

Karla J. Daniels ◽

Kevin L. Lu ◽

Guanghua Huang ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Candida Albicans ◽

Scaffold Protein ◽

White Cell ◽

Pheromone Response ◽

Content Type ◽

Pheromone Response Pathway ◽

Protein Map ◽

Mitogen Activated Protein ◽

Kinase Cascade

ABSTRACTAmong the hemiascomycetes, onlyCandida albicansmust switch from the white phenotype to the opaque phenotype to mate. In the recent evolution of this transition, mating-incompetent white cells acquired a unique response to mating pheromone, resulting in the formation of a white cell biofilm that facilitates mating. All of the upstream components of the white cell response pathway so far analyzed have been shown to be derived from the ancestral pathway involved in mating, except for the mitogen-activated protein (MAP) kinase scaffold protein, which had not been identified. Here, through binding and mutational studies, it is demonstrated that in both the opaque and the white cell pheromone responses, Cst5 is the scaffold protein, supporting the evolutionary scenario proposed. Although Cst5 plays the same role in tethering the MAP kinases as Ste5 does inSaccharomyces cerevisiae, Cst5 is approximately one-third the size and has only one rather than four phosphorylation sites involved in activation and cytoplasmic relocalization.IMPORTANCECandida albicansmust switch from white to opaque to mate. Opaque cells then release pheromone, which not only induces cells to mate but also in a unique fashion induces mating-incompetent white cells to form biofilms that facilitate opaque cell mating. All of the tested upstream components of the newly evolved white cell pheromone response pathway, from the receptor to the mitogen-activated protein (MAP) kinase cascade, are the same as those of the conserved opaque cell response pathway. One key element, however, remained unidentified, the scaffold protein for the kinase cascade. Here, we demonstrate that Cst5, a homolog of theSaccharomyces cerevisiaescaffold protein Ste5, functions as the scaffold protein in both the opaque and the white cell pheromone responses. Pheromone induces Cst5 phosphorylation, which is involved in activation and cytoplasmic localization of Cst5. However, Cst5 contains only one phosphorylation site, not four as in theS. cerevisiaeortholog Ste5. These results support the hypothesis that the entire upper portion of the newly evolved white cell pheromone response pathway is derived from the conserved pheromone response pathway in the mating process.

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The Evolutionary Rewiring of Ubiquitination Targets Has Reprogrammed the Regulation of Carbon Assimilation in the Pathogenic Yeast Candida albicans

mBio ◽

10.1128/mbio.00495-12 ◽

2012 ◽

Vol 3 (6) ◽

Cited By ~ 54

Author(s):

Doblin Sandai ◽

Zhikang Yin ◽

Laura Selway ◽

David Stead ◽

Janet Walker ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Fatty Acids ◽

Candida Albicans ◽

Isocitrate Lyase ◽

Carbon Sources ◽

Carbon Assimilation ◽

Pathogenic Yeast ◽

Content Type ◽

Catabolite Inactivation ◽

Accelerated Degradation

ABSTRACTMicrobes must assimilate carbon to grow and colonize their niches. Transcript profiling has suggested thatCandida albicans, a major pathogen of humans, regulates its carbon assimilation in an analogous fashion to the model yeastSaccharomyces cerevisiae, repressing metabolic pathways required for the use of alterative nonpreferred carbon sources when sugars are available. However, we show that there is significant dislocation between the proteome and transcriptome inC. albicans. Glucose triggers the degradation of theICL1andPCK1transcripts inC. albicans, yet isocitrate lyase (Icl1) and phosphoenolpyruvate carboxykinase (Pck1) are stable and are retained. Indeed, numerous enzymes required for the assimilation of carboxylic and fatty acids are not degraded in response to glucose. However, when expressed inC. albicans,S. cerevisiaeIcl1 (ScIcl1) is subjected to glucose-accelerated degradation, indicating that likeS. cerevisiae, this pathogen has the molecular apparatus required to execute ubiquitin-dependent catabolite inactivation.C. albicansIcl1 (CaIcl1) lacks analogous ubiquitination sites and is stable under these conditions, but the addition of a ubiquitination site programs glucose-accelerated degradation of CaIcl1. Also, catabolite inactivation is slowed inC. albicans ubi4cells. Ubiquitination sites are present in gluconeogenic and glyoxylate cycle enzymes fromS. cerevisiaebut absent from theirC. albicanshomologues. We conclude that evolutionary rewiring of ubiquitination targets has meant that following glucose exposure,C. albicansretains key metabolic functions, allowing it to continue to assimilate alternative carbon sources. This metabolic flexibility may be critical during infection, facilitating the rapid colonization of dynamic host niches containing complex arrays of nutrients.IMPORTANCEPathogenic microbes must assimilate a range of carbon sources to grow and colonize their hosts. Current views about carbon assimilation in the pathogenic yeastCandida albicansare strongly influenced by theSaccharomyces cerevisiaeparadigm in which cells faced with choices of nutrients first use energetically favorable sugars, degrading enzymes required for the assimilation of less favorable alternative carbon sources. We show that this is not the case inC. albicansbecause there has been significant evolutionary rewiring of the molecular signals that promote enzyme degradation in response to glucose. As a result, this major pathogen of humans retains enzymes required for the utilization of physiologically relevant carbon sources such as lactic acid and fatty acids, allowing it to continue to use these host nutrients even when glucose is available. This phenomenon probably enhances efficient colonization of host niches where sugars are only transiently available.

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High-Resolution Genome-Wide Occupancy in Candida spp. Using ChEC-seq

mSphere ◽

10.1128/msphere.00646-20 ◽

2020 ◽

Vol 5 (5) ◽

Author(s):

Faiza Tebbji ◽

Inès Khemiri ◽

Adnane Sellam

Keyword(s):

Public Health ◽

Gene Expression ◽

Saccharomyces Cerevisiae ◽

Candida Albicans ◽

High Resolution ◽

Transcriptional Regulator ◽

Candida Auris ◽

Content Type ◽

Genome Wide ◽

Public Health Threat

ABSTRACT To persist in their dynamic human host environments, fungal pathogens must sense and adapt by modulating their gene expression to fulfill their cellular needs. Understanding transcriptional regulation on a global scale would uncover cellular processes linked to persistence and virulence mechanisms that could be targeted for antifungal therapeutics. Infections associated with the yeast Candida albicans, a highly prevalent fungal pathogen, and the multiresistant related species Candida auris are becoming a serious public health threat. To define the set of a gene regulated by a transcriptional regulator in C. albicans, chromatin immunoprecipitation (ChIP)-based techniques, including ChIP with microarray technology (ChIP-chip) or ChIP-DNA sequencing (ChIP-seq), have been widely used. Here, we describe a new set of PCR-based micrococcal nuclease (MNase)-tagging plasmids for C. albicans and other Candida spp. to determine the genome-wide location of any transcriptional regulator of interest using chromatin endogenous cleavage (ChEC) coupled to high-throughput sequencing (ChEC-seq). The ChEC procedure does not require protein-DNA cross-linking or sonication, thus avoiding artifacts related to epitope masking or the hyper-ChIPable euchromatic phenomenon. In a proof-of-concept application of ChEC-seq, we provided a high-resolution binding map of the SWI/SNF chromatin remodeling complex, a master regulator of fungal fitness in C. albicans, in addition to the transcription factor Nsi1 that is an ortholog of the DNA-binding protein Reb1 for which genome-wide occupancy was previously established in Saccharomyces cerevisiae. The ChEC-seq procedure described here will allow a high-resolution genomic location definition which will enable a better understanding of transcriptional regulatory circuits that govern fungal fitness and drug resistance in these medically important fungi. IMPORTANCE Systemic fungal infections caused by Candida albicans and the “superbug” Candida auris are becoming a serious public health threat. The ability of these yeasts to cause disease is linked to their faculty to modulate the expression of genes that mediate their escape from the immune surveillance and their persistence in the different unfavorable niches within the host. Comprehensive knowledge on gene expression control of fungal fitness is consequently an interesting framework for the identification of essential infection processes that could be hindered by chemicals as potential therapeutics. Here, we expanded the use of ChEC-seq, a technique that was initially developed in the yeast model Saccharomyces cerevisiae to identify genes that are modulated by a transcriptional regulator, in pathogenic yeasts from the genus Candida. This robust technique will allow a better characterization of key gene expression regulators and their contribution to virulence and antifungal resistance in these pathogenic yeasts.

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Farnesol Induces Hydrogen Peroxide Resistance in Candida albicans Yeast by Inhibiting the Ras-Cyclic AMP Signaling Pathway

Eukaryotic Cell ◽

10.1128/ec.00321-09 ◽

2010 ◽

Vol 9 (4) ◽

pp. 569-577 ◽

Cited By ~ 66

Author(s):

Aurélie Deveau ◽

Amy E. Piispanen ◽

Angelyca A. Jackson ◽

Deborah A. Hogan

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Candida Albicans ◽

Adenylate Cyclase ◽

Signaling Pathway ◽

Stress Resistance ◽

Ros Generation ◽

Signaling Molecule ◽

Content Type ◽

Oxidative Stress Resistance

ABSTRACT Farnesol, a Candida albicans cell-cell signaling molecule that participates in the control of morphology, has an additional role in protection of the fungus against oxidative stress. In this report, we show that although farnesol induces the accumulation of intracellular reactive oxygen species (ROS), ROS generation is not necessary for the induction of catalase (Cat1)-mediated oxidative-stress resistance. Two antioxidants, α-tocopherol and, to a lesser extent, ascorbic acid effectively reduced intracellular ROS generation by farnesol but did not alter farnesol-induced oxidative-stress resistance. Farnesol inhibits the Ras1-adenylate cyclase (Cyr1) signaling pathway to achieve its effects on morphology under hypha-inducing conditions, and we demonstrate that farnesol induces oxidative-stress resistance by a similar mechanism. Strains lacking either Ras1 or Cyr1 no longer exhibited increased protection against hydrogen peroxide upon preincubation with farnesol. While we also observed the previously reported increase in the phosphorylation level of Hog1, a known regulator of oxidative-stress resistance, in the presence of farnesol, the hog1/hog1 mutant did not differ from wild-type strains in terms of farnesol-induced oxidative-stress resistance. Analysis of Hog1 levels and its phosphorylation states in different mutant backgrounds indicated that mutation of the components of the Ras1-adenylate cyclase pathway was sufficient to cause an increase of Hog1 phosphorylation even in the absence of farnesol or other exogenous sources of oxidative stress. This finding indicates the presence of unknown links between these signaling pathways. Our results suggest that farnesol effects on the Ras-adenylate cyclase cascade are responsible for many of the observed activities of this fungal signaling molecule.

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