Biology subjects

Shapiro, R. S.

Publications and source records attributed to Shapiro, R. S..

18 recordsLinked to original sources

bioRxiv2026

Non-homologous end-joining is implicated in rapid and efficient caspofungin adaptation in Nakaseomyces glabratus

Antifungal resistance in Nakaseomyces glabratus is a major clinical challenge, yet the cellular processes that shape its evolution remain poorly understood. Here, we used experimental evolution to investigate the role of the error-prone double-strand break repair pathway, non-homologous end joining (NHEJ), in adaptation to fluconazole and caspofungin. Wild-type and NHEJ-deficient (lig4{Delta}) populations were evolved under antifungal selection for 25 days. Fluconazole resistance emerged rapidly in both genetic backgrounds and was associated with recurrent PDR1 mutations and aneuploidies. In contrast, caspofungin adaptation was delayed and less efficient in lig4{Delta} populations, with several lineages failing to survive. All wild-type caspofungin-evolved isolates carried canonical FKS2 hotspot mutations, whereas lig4{Delta} isolates predominantly acquired resistance through alternative genetic pathways. Caspofungin adaptation also frequently conferred cross-resistance to fluconazole and was accompanied by changes in the abundance of ergosterol-associated proteins. Together, these findings implicate NHEJ in promoting efficient evolution of FKS-mediated echinocandin resistance and demonstrate that DNA repair capacity can shape antifungal resistance trajectories in N. glabratus.

microbiology↗

bioRxiv2026

Differential requirement for the Ire1 luminal domain in Candida albicans drug susceptibility and pathogenicity

The opportunistic human pathogen Candida albicans depends on the unfolded protein response (UPR) for cell wall integrity, antifungal tolerance, filamentous growth, and virulence. The UPR is driven by the conserved transmembrane sensor Ire1, which is activated either by misfolded proteins through its luminal domain or by lipid bilayer stress (LBS) through its transmembrane domain. In budding yeast, these two activation modes deploy divergent transcriptional programs. Whether the requirement for these two input domains is separable in C. albicans, where the cell membrane and cell wall are themselves the targets of major antifungal drug classes, remains unknown. Here, we engineered a C. albicans strain expressing Ire1 lacking an intact luminal domain (ire1{Delta}LD), which no longer detects proteotoxic stress. The ire1{Delta}LD strain grew in the presence of the azole antifungals fluconazole and miconazole but was highly sensitive to heat shock, cell wall stress, and the echinocandin caspofungin. It was also unable to sustain filamentous growth and showed reduced virulence in a Caenorhabditis elegans infection model. RNA sequencing revealed only modest changes to the steady-state transcriptome of ire1{Delta}LD cells. Together, these findings define a differential requirement for the input domains of C. albicans Ire1, uncoupling growth under azole-induced membrane stress from the cell wall, thermal, and virulence-associated outputs that depend on proteotoxic sensing, a distinction that could inform antifungal strategies targeting the UPR.

cell biology↗

bioRxiv2026

CRISPR-activation reveals key resistance genes and vulnerabilities of copy number variants in Candida albicans

Changes in gene copy number are an extremely important source of variation and are frequently observed during the acquisition of drug resistance. The opportunistic human fungal pathogen Candida albicans frequently adapts to antifungal drugs via large copy number variations (CNVs) that amplify hundreds of genes simultaneously. Despite the recurrent amplification of CNVs across diverse clinical isolates, the genes that contribute to drug resistance are not known. Additionally, by amplifying many genes, CNVs might result in cross-adaptation or fitness trade-offs to multiple environments, which has major implications for how CNVs are expected to contribute to adaptation in complex environments like a mammalian host. We use CRISPR-activation to systematically assay the fitness effects of individually overexpressing [~]800 genes in four genetically diverse isolates across eight physiologically relevant environments. We identify 198 genes with significant fitness effects in at least one environment in one or more genetic backgrounds. We identify novel genes with positive fitness effects in two different classes of antifungal drug and observe frequent gene-by-environment interactions for the fitness effects of gene overexpression. Additive fitness effects of individual gene overexpression are a significant predictor of the fitness of multiple isolates with CNVs and can explain fitness trade-offs observed between classes of antifungal drug for the CNV isolates. These findings identify genes that increase fitness in drug and those that create vulnerabilities in CNV isolates and can help inform treatment of isolates adapting to antifungal drug via CNVs.

microbiology↗

bioRxiv2026

Chromosome-scale CRISPR screening reveals secretory pathway genes as drivers of aneuploidy-mediated antifungal tolerance

The gain or loss of chromosomes in eukaryotes often drives aberrant phenotypes by altering the expression levels of hundreds or thousands of genes. In the case of beneficial aneuploidies, the genetic basis of fitness improvement has rarely been pinpointed, and identifying the causal genes remains a major challenge in engineering biology. The leading cause of human fungal infections, Candida albicans, frequently acquires extra copies of chromosome R (ChrR) following exposure to azole antifungal drugs, resulting in heightened antifungal tolerance. Here, we combine RNA-seq with parallel chromosome-wide CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) screens to systematically profile the ChrR genes contributing to azole tolerance. Using multiplexed CRISPR-dCas12a tools, we further characterize the combinatorial effects of candidate genes and uncover a central role for post-Golgi secretory trafficking in antifungal tolerance. Specifically, we demonstrate that the secretory pathway regulators SEC4 and YPT31 are both necessary and sufficient for ChrR-mediated azole tolerance. By leveraging a large-scale CRISPRa screen in a fungal pathogen, our work functionally dissects one of the most common aneuploidies observed in C. albicans, provides mechanistic insight into the molecular basis of antifungal tolerance, and establishes a generalizable framework for studying aneuploidy-mediated phenotypes across eukaryotic organisms.

microbiology↗

bioRxiv2025

Pooled CRISPRi screening reveals fungal-specific vulnerabilities across environments and genetic backgrounds

The rising rate of drug-resistant fungal infections and the emergence of fungal pathogens with intrinsic resistance phenotypes are a growing concern. The close evolutionary distance between mammals and fungi complicates the design of new antifungals and increases the chances of toxic off-target effects. As such, antifungal drug development usually focuses on fungal-specific proteins when considering potential new targets. Ideal drug targets should mediate essential cell processes and be highly sensitive to inhibition. Targeted gene repression can serve as a model for drug-mediated inhibition and for determining the dosage-sensitivity profile of genes of interest. In the fungal pathogen Candida albicans, classical approaches for gene repression can be labour-intensive and limited to one genetic background due to low throughput. Here, we adapt pooled CRISPRi screening in C. albicans for the first time and exploit this technique for large-scale functional genomic analysis. Through pooled CRISPRi screening, we test the repression sensitivity of over a hundred essential genes conserved in fungi but absent in humans, and successfully identify highly dosage-sensitive genes across multiple cell components and pathways. By extending our analysis to ten diverse environmental conditions, we show how the environment influences dosage-sensitivity profiles. Finally, we extend our experiments to two clinical drug-resistant C. albicans strain backgrounds and demonstrate that many of the fitness defects we observed are conserved in resistant clinical isolates. Together, our results highlight a set of genes that are highly dosage-sensitive across different genetic and environmental contexts, making them attractive targets for further investigation. By facilitating rapid, efficient large-scale functional genomics assays across diverse genetic backgrounds, CRISPRi pooled screening will open new frontiers in C. albicans biology.

microbiology↗

bioRxiv2025

Distinct Ire1-driven transcriptional responses control morphogenesis in Candida albicans

The pathogenic yeast Candida albicans relies on morphogenesis--the transition from spherical yeast to filamentous hyphal forms--for infection. While morphogenesis requires Ire1, a transmembrane protein that canonically initiates the Unfolded Protein Response (UPR) through HAC1 mRNA splicing, the specific mechanisms linking Ire1 to filamentation remain unclear. Using transcriptome analysis, we found that the Ire1-dependent transcriptional response driving morphogenesis is fundamentally distinct from the canonical UPR response to proteotoxic stress, with minimal overlap between programs. Remarkably, morphogenesis occurs without detectable HAC1 splicing, and HAC1 deletion only partially impairs filamentation, unlike complete loss with IRE1 deletion. These findings establish that Ire1 regulates hyphal development through previously uncharacterized HAC1-independent pathways. Our data reveal decreased transcription of secretory proteins in an Ire1-dependent manner, providing compelling evidence that C. albicans possesses regulated Ire1-dependent decay (RIDD) activity--a post-transcriptional mechanism not previously characterized in this pathogen. Additionally, we identify cell wall integrity as a key HAC1-independent mechanism, with Ire1--but not Hac1--essential for cell wall stress tolerance and upregulation of cell wall biosynthesis genes during filamentation. Given Ire1s essential role in pathogenesis and extensive development of Ire1-targeting compounds for mammalian systems, our findings position Ire1 as a highly promising druggable target for novel antifungal therapeutics and development of fungal-specific inhibitors.

cell biology↗

bioRxiv2025

The Unique Efg1 Fungal Virulence Regulon in the Catheterized Bladder Environment

Urinary catheterization, a common procedure in hospitals and nursing home facilities, is a primary driver of hospital-acquired infections (HAI). These devices frequently lead to catheter-associated urinary tract infections (CAUTIs), which often progress to severe complication, sepsis, and ultimately death. The fungus Candida albicans has emerged as the second most common causative agent of CAUTIs; yet, its pathogenesis is poorly understood, which complicates development of efficient treatments. Previously, we identified the transcription factor Efg1 as a critical virulence driver in C. albicans CAUTIs. However, its specific downstream targets within the unique bladder microenvironment remained unknown. This study identifies, for the first time, the complete Efg1 regulon that is active during growth in human urine. We confirmed the clinical relevance of this discovery, finding that many of these Efg1-regulated factors are present and significantly upregulated in catheter samples from patients with C. albicans infections. Furthermore, we characterized two of these key factors, ECE1 and EED1, validating their roles both in vitro in urine conditions and in vivo using a CAUTI mouse model. Identifying the tissue-specific downstream targets of Efg1 elucidates the precise mechanism of fungal CAUTI. This knowledge provides a new roadmap for developing targeted therapeutics, offering vital antimicrobial-sparing strategies to combat these life-threatening infections. SIGNIFICANCECatheter-associated urinary tract infections (CAUTIs) are common hospital-acquired infections that can lead to severe complications and death. Although most are caused by bacteria, the fungus Candida albicans is an increasingly prevalent cause, yet the pathogenesis of fungal CAUTIs is poorly understood. Previous research identified Efg1 as necessary for CAUTI, and now this study defines the urine-specific Efg1 regulon, validating its clinical relevance in catheter samples from infected patients. We further assessed how key downstream factors, Ece1 and Eed1, contribute to bladder infection. This first report of the urine-specific EFG1 network provides new targets for diagnosing and treating these life-threatening infections.

microbiology↗

bioRxiv2025

HyperdCas12a-Based Multiplexed Genetic Regulation in Candida albicans

Complex microbial phenotypes involve the combined activity of diverse gene regulatory networks. However, the majority of reverse genetics approaches in microbial pathogenesis research have focused on single-gene perturbation studies, in part due to the lack of available genetic tools in many pathogens. Developing enhanced versions of CRISPR-Cas platforms holds significant promise for improving the scalability of microbial functional genomics research. Here, we demonstrate highly efficient, inducible, and multiplexed activation and repression in the major human fungal pathogen Candida albicans by translating the hyperdCas12a variant to the fungal kingdom. This represents the first application of a CRISPR-Cas12 system in a human fungal pathogen. We profile the effectiveness of our new CRISPRa and CRISPRi tools and achieve tunable levels of target modulation. Further, we demonstrate that perturbing combinations of genes in the drug efflux and ergosterol biosynthesis pathways reveals important redundancies and synergistic properties in drug resistance circuitry. Our hyperdCas12a platform is thus an efficient system for the rapid generation of combinatorial mutants that will enable the mechanistic understanding of genetic interactions involved in diverse phenotypes in C. albicans. The enhanced activity with hyperdCas12a in fungi suggests it could be translated to other microbes as a powerful tool for studying genetic interactions.

genetics↗

bioRxiv2025

Targeted loss of heterozygosity in Candida albicans using CRISPR-Cas9

The diploid genome of the fungal pathogen Candida albicans is highly heterozygous, with most allele pairs diverging at either the coding or regulatory level. When faced with selection pressure like antifungal exposure, this hidden genetic diversity can provide a reservoir of adaptive mutations through loss of heterozygosity (LOH) events. Validating the potential phenotypic impact of LOH events observed in clinical or experimentally evolved strains can be difficult due to the challenge of precisely targeting one allele over the other. Here, we show that a CRISPR-Cas9 system can be used to overcome this challenge. By designing allele-specific guide RNA sequences, we can induce targeted, directed LOH events, which we validate by whole-genome long-read sequencing. Using this approach, we efficiently recapitulate a recently described LOH event that increases resistance to the antifungal fluconazole. Additionally, we find that the recombination tracts of these induced LOH events have similar lengths to those observed naturally. To facilitate future use of this method, we provide a database of allele-specific sgRNA sequences for Cas9 that provide near genome-wide coverage of heterozygous sites through either direct or indirect targeting. This approach will be useful in probing the adaptive role of LOH events in this important human pathogen.

microbiology↗

bioRxiv2024

A role for the putative error-prone polymerase REV1 in DNA damage and antifungal drug resistance in Candida albicans

Antimicrobial-induced DNA damage, and subsequent repair via upregulation of DNA repair factors, including error-prone translesion polymerases, can lead to the increased accumulation of mutations in the microbial genome, and ultimately increased risk of acquired mutations associated with antimicrobial resistance. While this phenotype is well described in bacterial species, it is less thoroughly investigated amongst microbial fungi. Here, we monitor DNA damage induced by antifungal agents in the fungal pathogen Candida albicans, and find that commonly used antifungal drugs are able to induce DNA damage, leading to the upregulation of transcripts encoding predicted error-prone polymerases and related factors. We focus on REV1, encoding a putative error-prone polymerase, and find that while deleting this gene in C. albicans leads to increased sensitivity to DNA damage, it also unexpectedly renders cells more likely to incur mutations and evolve resistance to antifungal agents. We further find that deletion of REV1 leads to a significant depletion in the uncharacterized protein Shm1, which itself plays a role in fungal mutagenesis. Together, this work lends new insight into previously uncharacterized factors with important roles in the DNA damage response, mutagenesis, and the evolution of antifungal drug resistance.

microbiology↗

bioRxiv2023

Most azole antifungal resistance mutations in the drug target provide cross-resistance and carry no intrinsic fitness cost

Azole antifungals are among the most frequently used drugs to treat fungal infections. Amino acid substitutions in and around the binding site of the azole target Erg11 (Cyp51) are a common resistance mechanism in pathogenic yeasts such as Candida albicans. How many and which mutations confer resistance, and at what cost, is however largely unknown. Here, we measure the impact of nearly 4,000 amino acid variants of the Erg11 ligand binding pocket on the susceptibility to six medical azoles. We find that a large fraction of amino acid substitutions lead to resistance (33%), most resistance mutations confer cross-resistance to two or more azoles (88%) and most importantly, only a handful of resistance mutations show a significant fitness cost in the absence of drug (9%). Our results reveal that resistance to azoles can arise through a large set of mutations and this will likely lead to azole pan-resistance, with very little evolutionary compromise. Such a resource will help inform treatment choices in clinical settings and guide the development of new drugs.

microbiology↗

bioRxiv2023

Functional genetic characterization of stress tolerance and biofilm formation in Nakaseomyces glabrata via a novel CRISPR activation system

The overexpression of genes frequently arises in Nakaseomyces (formerly Candida) glabrata via gain-of-function mutations, gene duplication or aneuploidies, with important consequences on pathogenesis traits and antifungal drug resistance. This highlights the need to develop specific genetic tools to mimic and study genetic amplification in this important fungal pathogen. Here, we report the development, validation, and applications of the first CRISPR activation (CRISPRa) system in N. glabrata for targeted genetic overexpression. Using this system, we demonstrate the ability of CRISPRa to drive high levels of gene expression in N. glabrata, and further assess optimal guide RNA targeting for robust overexpression. We demonstrate the applications of CRISPRa to overexpress genes involved in fungal pathogenesis and drug resistance, and detect corresponding phenotypic alterations in these key traits, including the characterization of novel phenotypes. Finally, we capture strain variation using our CRISPRa system in two commonly used N. glabrata genetic backgrounds. Together, this tool will expand our capacity for functional genetic overexpression in this pathogen, with numerous possibilities for future applications.

microbiology↗

bioRxiv2023

Evolutionary diversity of the control of the azole response by Tra1 across yeast species

Tra1 is an essential co-activator protein of the yeast SAGA and NuA4 acetyltransferase complexes that regulate gene expression through multiple mechanisms including the acetylation of histone proteins. Tra1 is a pseudokinase of the PIKK family characterized by a C-terminal PI3K domain with no known kinase activity. However, mutations of specific arginine residues to glutamine in the PI3K domains (an allele termed tra1Q3) result in reduced growth and increased sensitivity to multiple stresses. In the opportunistic fungal pathogen Candida albicans, the tra1Q3 allele reduces pathogenicity and increases sensitivity to the echinocandin antifungal drug caspofungin, which disrupts the fungal cell wall. Here, we found that loss of Tra1 function, in contrast to what is seen with caspofungin, increases tolerance to the azole class of antifungal drugs, which inhibits ergosterol synthesis. In C. albicans, tra1Q3 increases expression of genes linked to azole resistance, such as ERG11 and CDR1. CDR1 encodes a multidrug ABC transporter associated with efflux of multiple xenobiotics, including azoles. Consequently, cells carrying tra1Q3 show reduced intracellular accumulation of fluconazole. In contrast, a tra1Q3 S. cerevisiae strain displayed opposite phenotypes: decreased tolerance to azole, decreased expression of the efflux pump PDR5 and increased intracellular accumulation of fluconazole. Therefore, our data provide evidence that Tra1 differentially regulates the antifungal response across yeast species.

genetics↗

bioRxiv2022

Antimicrobial susceptibility testing for diverse Malassezia species

The genus Malassezia is an opportunistic lipid-dependent yeast that is associated with common skin diseases and has recently been associated with Crohns disease and certain cancers. Understanding the susceptibility of Malassezia to diverse antimicrobial agents is crucial for identifying effective antifungal therapies. Here, we tested the efficacy of isavuconazole, itraconazole, terbinafine and artemisinin against three Malassezia species: M. restricta, M. slooffiae, and M. sympodialis, using microbroth dilution techniques. We found antifungal properties for the two previously-unstudied antimicrobials: isavuconazole and artemisinin. Overall all Malassezia species were particularly susceptible to itraconazole, with a MIC range from 0.0015 to 0.1562 M. ImportanceThe Malassezia genus is known to be a cause of skin conditions and has recently been associated with diseases such as Crohns disease, pancreatic ductal carcinoma and breast cancer. This work was completed to assess the susceptibility to a variety of antimicrobial drugs on diverse Malassezia species, in particular Malassezia restricta.

microbiology↗

bioRxiv2022

Development and applications of a CRISPR activation system for facile genetic overexpression in Candida albicans

For the fungal pathogen Candida albicans, genetic overexpression readily occurs via a diversity of genomic alterations, such as aneuploidy and gain-of-function mutations, with important consequences for host adaptation, virulence, and evolution of antifungal drug resistance. Given the important role of overexpression on C. albicans biology, it is critical to develop and harness tools that enable the analysis of genes expressed at high levels in the fungal cell. Here, we describe the development, optimization, and application of a novel, single-plasmid-based CRISPR activation (CRISPRa) platform for targeted genetic overexpression in C. albicans, which employs a guide RNA to target an activator complex to the promoter region of a gene of interest, thus driving transcriptional expression of that gene. Using this system, we demonstrate the ability of CRISPRa to drive high levels of gene expression in C. albicans, and we assess optimal guide RNA targeting for robust and constitutive overexpression. We further demonstrate the specificity of the system via RNA sequencing. We highlight the application of CRISPRa to overexpress genes involved in pathogenesis and drug resistance and contribute towards the identification of novel phenotypes. Together, this tool will facilitate a broad range of applications for the study of C. albicans genetic overexpression.

microbiology↗

bioRxiv2021

The SAGA and NuA4 component Tra1 regulates Candida albicans drug resistance and pathogenesis

Candida albicans is the most common cause of death from fungal infections. Emergence of resistant strains reducing the efficacy of first line therapy with echinocandins such as caspofungin calls for the identification of alternative therapeutic strategies. Tra1 is an essential component of the SAGA and NuA4 transcriptional co-activator complexes. As a PIKK family member, Tra1 is characterized by a C-terminal phosphoinositide 3-kinase domain. In Saccharomyces cerevisiae, the assembly and function of SAGA and NuA4 is compromised by a version of Tra1 (Tra1Q3) with three arginine residues in the putative ATP-binding cleft changed to glutamine, Whole transcriptome analysis of the S. cerevisiae tra1Q3 strain highlights Tra1s role in global transcription, stress response and cell wall integrity. As a result, tra1Q3 increases susceptibility to multiple stressors, including caspofungin. Moreover, the same tra1Q3 allele in the pathogenic yeast Candida albicans causes similar phenotypes, suggesting that Tra1 broadly mediates the antifungal response across yeast species. Transcriptional profiling in C. albicans identified 68 genes that were differentially expressed when the tra1Q3 strain was treated with caspofungin, as compared to gene expression changes induced by either tra1Q3 or caspofungin alone. Included in this set were genes involved in cell wall maintenance, adhesion and filamentous growth. Indeed, the tra1Q3 allele reduces filamentation and other pathogenesis traits in C. albicans. We identified EVP1, which encodes a putative plasma membrane protein, amongst the Tra1-regulated genes, Disrupting EVP1 results in reduced filamentation and infection capacity in C. albicans. Thus,Tra1 emerges as a promising therapeutic target for fungal infections. ImportanceFungal pathogens such as Candida albicans are important agents of infectious disease, with increasing rates of drug resistance, and limited available antifungal therapeutics. In this study, we characterize the role of C. albicans Tra1, a critical component of acetyltransferase complexes, involved in transcriptional regulation and responses to environmental stress. We find C. albicans genetic mutants with impaired Tra1 function have reduced tolerance to cell-wall targeting stressors, including the clinically-important antifungal caspofungin. We further use RNA-sequencing to profile the global fungal response to the tra1 mutation, and identify a previously uncharacterized C. albicans gene, EVP1. We find that both TRA1 and EVP1 play an important role in phenotypes associated with fungal pathogenesis, including cellular morphogenesis, biofilm formation, and toxicity towards host immune cells. Together, this work describes the key role for Tra1 in regulating fungal drug tolerance and pathogenesis, and positions this protein as a promising therapeutic target for fungal infections.

microbiology↗

bioRxiv2020

Systematic characterization and genetic interaction analysis of adhesins in Candida albicans virulence

Candida albicans is a microbial fungus that exists as a commensal member of the human microbiome and an opportunistic pathogen. Cell surface-associated adhesin proteins play a crucial role in C. albicans ability to undergo cellular morphogenesis, develop robust biofilms, colonize, and cause infection in a host. However, a comprehensive analysis of the role and relationships between these adhesins has not been explored. We previously established a CRISPR-based platform for efficient generation of single- and double-gene deletions in C. albicans, which was used to construct a library of 144 mutants, comprising 12 unique adhesin genes deleted singly, or in every possible combination of double deletions. Here, we exploit this adhesin mutant library to explore the role of adhesin proteins in C. albicans virulence. We perform a comprehensive, high-throughput screen of this library, using Caenorhabditis elegans as a simplified model host system, which identified mutants critical for virulence and significant genetic interactions. We perform follow-up analysis to assess the ability of high- and low-virulence strains to undergo cellular morphogenesis and form biofilms in vitro, as well as to colonize the C. elegans host. We further perform genetic interaction analysis to identify novel significant negative genetic interactions between adhesin mutants, whereby combinatorial perturbation of these genes significantly impairs virulence, more than expected based on virulence of the single mutant constituent strains. Together, this yields important new insight into the role of adhesins, singly and in combinations, in mediating diverse facets of virulence of this critical fungal pathogen. SummaryCandida albicans is a human fungal pathogen and cause of life-threatening systemic infections. Cell surface-associated adhesins play a central role in this pathogens ability to establish infection. Here, we provide a comprehensive analysis of adhesin factors, and their role in fungal virulence. Exploiting a high-throughput workflow, we screened an adhesin mutant library using C. elegans as a simple model host, and identified mutants and genetic interactions involved in virulence. We found that adhesin mutants are impaired in in vitro pathogenicity, irrespective of their virulence. Together, this work provides new insight into the role of adhesin factors in mediating fungal virulence.

microbiology↗

bioRxiv2018

Metabolism-Induced Oxidative Stress and DNA Damage Selectively Trigger Genome Instability in Polyploid Cells

Understanding the forces impacting genome stability is important for diverse processes such as tumorigenesis and reproductive biology. The pathogenic yeast Candida albicans displays unusual genome dynamics in which tetraploid cells, but not diploid cells, become unstable when grown on a glucose-rich pre-sporulation medium. Here, we reveal that C. albicans polyploid cells are metabolically hyperactive on this medium as evidenced by increased expression of metabolic genes as well as higher rates of fermentation and oxidative respiration. These cells also show elevated levels of reactive oxygen species (ROS), activate the ROS-responsive transcription factor Cap1, and accrue DNA double-strand breaks. Suppression of ROS levels reduced oxidative stress, DNA damage and chromosome instability. These studies reveal how metabolic flux can generate endogenous ROS, triggering DNA damage and genome instability in polyploid, but not diploid, cells. We discuss parallels with metabolism-induced instability in cancer cells and propose that ROS-induced DNA damage could have facilitated ploidy cycling in eukaryotes prior to the evolution of meiosis.

microbiology↗