Biology subjects

Croll, D.

Publications and source records attributed to Croll, D..

At least 73 records · Page 4Linked to original sources

bioRxiv2020

Mapping the adaptive landscape of a major agricultural pathogen reveals evolutionary constraints across heterogeneous environments

The adaptive potential of pathogens in novel or heterogeneous environments underpins the risk of disease epidemics. Antagonistic pleiotropy or differential resource allocation among life-history traits can constrain pathogen adaptation. However, we lack understanding how the genetic architecture of individual traits can generate trade-offs. Here, we report a large-scale study based on 145 global strains of the fungal wheat pathogen Zymoseptoria tritici from four continents. We measured 50 life-history traits, including virulence and reproduction on 12 different wheat hosts and growth responses to several abiotic stressors. To elucidate the genetic basis of adaptation, we used multi-trait genome-wide association mapping. We show that most traits are governed by polygenic architectures and are highly heritable suggesting that adaptation proceeds mainly through allele frequency shifts at many loci. We identified numerous pleiotropic SNPs with conflicting effects on host colonization and survival in stressful environments. Such genetic constraints are likely limiting the pathogens ability to cause host damage and could be exploited for pathogen control. In contrast, adaptation to abiotic stress factors was likely facilitated by synergistic pleiotropy. Our study illustrates how comprehensive mapping of life-history trait architectures across diverse environments allows to predict evolutionary trajectories of pathogens confronted with environmental perturbations.

evolutionary biology↗

bioRxiv2020

The complex genomic basis of rapid convergent adaptation to pesticides across continents in a fungal plant pathogen

Convergent evolution leads to identical phenotypic traits in different species or populations. Convergence can be driven by standing variation allowing selection to favor identical alleles in parallel or the same mutations can arise independently. However, the molecular basis of such convergent adaptation remains often poorly resolved. Pesticide resistance in agricultural ecosystems is a hallmark of convergence in phenotypic traits. Here, we analyze the major fungal pathogen Zymoseptoria tritici causing serious losses on wheat and with parallel fungicide resistance emergence across continents. We sampled three population pairs each from a different continent spanning periods early and late in the application of fungicides. To identify causal loci for resistance, we combined knowledge from molecular genetics work and performed genome-wide association studies (GWAS) on a global set of isolates. We discovered yet unknown factors in azole resistance including membrane stability functions. We found strong support for the hotspot model of resistance evolution with parallel changes in a small set of loci but additional loci showed more population-specific allele frequency changes. Genome-wide scans of selection showed that half of all known resistance loci were overlapping a selective sweep region. Hence, the application of fungicides was one of the major selective agents acting on the pathogen over the past decades. Furthermore, loci identified through GWAS showed the highest overlap with selective sweep regions underlining the importance to map phenotypic trait variation in evolving populations. Our population genomic analyses showed that both de novo mutations and gene flow likely contributed to the parallel emergence of resistance.

evolutionary biology↗

bioRxiv2020

Comparative genomics analyses of lifestyle transitions at the origin of an invasive fungal pathogen in the genus Cryphonectria

Emerging fungal pathogens are a threat to forest and agroecosystems, as well as animal and human health. How pathogens evolve from non-pathogenic ancestors is still poorly understood making the prediction of future outbreaks challenging. Most pathogens have evolved lifestyle adaptations, which were enabled by specific changes in the gene content of the species. Hence, understanding transitions in the functions encoded by genomes gives valuable insight into the evolution of pathogenicity. Here, we studied lifestyle evolution in the genus Cryphonectria, including the prominent invasive pathogen C. parasitica, the causal agent of chestnut blight on Castanea species. We assembled and compared the genomes of pathogenic and putatively non-pathogenic Cryphonectria species, as well as sister group pathogens in the family Cryphonectriaceae (Diaporthales, Ascomycetes) to investigate the evolution of genome size and gene content. We found a striking loss of genes associated with carbohydrate metabolism (CAZymes) in C. parasitica compared to other Cryphonectriaceae. Despite substantial CAZyme gene loss, experimental data suggests that C. parasitica has retained wood colonization abilities shared with other Cryphonectria species. Putative effectors substantially varied in number, cysteine content and protein length among species. In contrast, secondary metabolite gene clusters show a high degree of conservation within the genus. Overall, our results underpin the recent lifestyle transition of C. parasitica towards a more pathogenic lifestyle. Our findings suggest that a CAZyme loss may have promoted pathogenicity of C. parasitica on chestnuts. Analyzing gene complements underlying key nutrition modes can facilitate the detection of species with the potential to emerge as pathogens.

microbiology↗

bioRxiv2020

Population-level deep sequencing reveals the interplay of clonal and sexual reproduction in the fungal wheat pathogen Zymoseptoria tritici

Pathogens can rapidly surmount crop resistance challenging global food security. On annual crops, pathogens must re-infect from environmental sources at the beginning of every growing season. Fungal pathogens evolved mixed reproductive strategies to cope with the distinct life cycle challenges of colonizing plants, spreading within fields and ultimately producing propagules for survival in winter. However, how genotypic diversity evolves over this period remains largely unknown. Here, we performed a deep hierarchical sampling in a single experimental wheat field infected by the major fungal pathogen Zymoseptoria tritici. We analyzed whole genome sequences of 177 isolates collected from twelve distinct cultivars replicated in space at three time points of the growing season. The field population was highly diverse with 37 SNPs per kilobase and a linkage disequilibrium decay within 200-700 bp. We found that ~20% of the individual isolates were grouping into 15 clonal groups. Pairs of clones were disproportionally found at short distance (<5m) but a low degree of dispersal occurred also at the scale of the entire field consistent with a predominant leaf-to-leaf dispersal. We found no association of wheat cultivars and clonal genotypes with the exception of one cultivar. Surprisingly, levels of clonality did not increase over time in the field although reproduction is thought to be exclusively asexual during the growing season. Our study shows that the pathogen establishes vast and stable gene pools in single fields over the growing season. Monitoring short-term evolutionary changes in crop pathogens will inform more durable strategies to contain diseases.Competing Interest StatementThe authors have declared no competing interest.View Full Text

genomics↗

bioRxiv2020

A chromosome-scale genome assembly for the Fusarium oxysporum strain Fo5176 to establish a model Arabidopsis-fungal pathosystem

Plant pathogens cause widespread yield losses in agriculture. Understanding the drivers of plant-pathogen interactions requires decoding the molecular dialog leading to either resistance or disease. However, progress in deciphering pathogenicity genes has been severely hampered by suitable model systems and incomplete fungal genome assemblies. Here, we report a significant improvement of the assembly and annotation of the genome of the Fusarium oxysporum (Fo) strain Fo5176. Fo comprises a large number of serious plant pathogens on dozens of plant species with largely unresolved pathogenicity factors. The strain Fo5176 infects Arabidopsis thaliana and, hence, constitutes a highly promising model system. We use high-coverage Pacific Biosciences Sequel long-read and Hi-C sequencing data to assemble the genome into 19 chromosomes and a total genome size of 67.98 Mb. The genome has a N50 of 4 Mb and a 99.1% complete BUSCO score. Phylogenomic analyses based on single-copy orthologs clearly place the Fo5176 strain in the Fo f sp. conglutinans clade as expected. We generated RNAseq data from culture medium and plant infections to train gene predictions and identified [~]18,000 genes including ten effector genes known from other Fo clades. We show that Fo5176 is able to infect cabbage and Brussel sprouts of the Brassica oleracea, expanding the usefulness of the Fo5176 model pathosystem. Finally, we performed large-scale comparative genomics analyses comparing the Fo5176 to 103 additional Fo genomes to define core and accessory genomic regions. In conjunction with the molecular tool sets available for A. thaliana, the Fo5176 genome and annotation provides a crucial step towards the establishment of a highly promising pathosystem.

genomics↗

bioRxiv2020

Maintenance of variation in virulence and reproduction in populations of an agricultural plant pathogen

Genetic diversity within pathogen populations is critically important for predicting pathogen evolution, disease outcomes and prevalence. However, we lack a good understanding of the processes maintaining genetic variation and constraints on pathogen life-history evolution. Here, we analyzed interactions between 12 wheat host genotypes and 145 strains of Zymoseptoria tritici from five global populations to investigate the evolution and maintenance of variation in pathogen virulence and reproduction. We found a strong positive correlation between virulence and reproduction, with substantial variation in both traits maintained within each pathogen population. On average, highly virulent isolates exhibited higher fecundity, which might increase transmission potential in agricultural fields planted to homogeneous hosts at a high density. We further showed that pathogen strains with a narrow host range (i.e. specialists) for fecundity were on average less virulent, and those with a broader host range (i.e. generalists) for virulence were on average less fecund on a given specific host. These trade-offs costs associated with host specialization might constrain the directional evolution of virulence and fecundity. We conclude that selection favoring pathogen strains that are virulent across diverse hosts, coupled with selection that maximizes fecundity on specific hosts, may explain the maintenance of these pathogenicity traits within and among pathogen populations.

evolutionary biology↗

bioRxiv2020

The genetic architecture of emerging fungicide resistance in populations of a global wheat pathogen

Containing fungal diseases often depends on the application of fungicidal compounds. Fungicides can rapidly lose effectiveness due to the rise of resistant individuals in populations. However, the lack of knowledge about resistance mutations beyond known target genes challenges investigations into pathways to resistance. We used whole-genome sequencing data and association mapping to reveal the multilocus genetic architecture of fungicide resistance in a global panel of 159 isolates of Parastagonospora nodorum, an important fungal pathogen of wheat. We found significant differences in azole resistance among global field populations. The populations evolved distinctive combinations of resistance alleles which can interact synergistically. We identified 34 significantly associated SNPs located in close proximity to genes associated with fungicide resistance in other fungi, including an MFS transporter. Using fungal colony growth rates and melanin production at different temperatures as fitness proxies, we found no evidence that resistance was constrained by genetic trade-offs. Our study demonstrates how genome-wide association studies of a global collection of pathogen strains can recapitulate the emergence of fungicide resistance. The distinct complement of resistance mutations found among populations illustrates how the evolutionary trajectory of fungicide adaptation can be complex and challenging to predict.

genomics↗

bioRxiv2020

A reference transcriptome for the early-branching fern Botrychium lunaria enables fine-grained resolution of population structure

Ferns are the second most dominant group of land plants after angiosperms. Extant species occupy an extensive range of habitats and contribute significantly to ecosystem functioning. Despite the importance of ferns, most taxa are poorly covered by genomic resources. The genus Botrychium belongs to the family Ophioglossaceae, one of the earliest divergent lineages of vascular plants, and has a cosmopolitan distribution with 35 species, half of which are polyploids. Here, we establish a transcriptome for Botrychium lunaria, a diploid species with an extremely large genome with a 1C value of 12.10 pg. We assembled 25,701 high-quality transcripts with an average length of 1,332 bp based on deep RNA-sequencing of a single individual. We sequenced an additional 11 transcriptomes of individuals from two populations in Switzerland, including the population of the reference individual. Based on read mapping to reference transcript sequences, we identified 374,510 single nucleotide polymorphisms (SNPs) segregating among individuals for an average density of 14 SNPs per kb. The transcriptome-wide markers provided unprecedented resolution of the population genetic structure revealing substantial variation in heterozygosity among individuals. We also constructed a phylogenomic tree of 90 taxa representing all fern orders to ascertain the placement of the genus Botrychium. The high-quality transcriptomic resources enable powerful population and phylogenomic studies in an important group of ferns. Significance statementFerns pose substantial puzzles in terms of lifestyles, genome organization and population structure. Progress has been significantly hampered by the lack of genomic resources. Here, we present a transcriptome for Botrychium lunaria, a phylogenetically early-branching fern with an extremely large genome. We show that the new transcriptome improves phylogenetic resolution among early-branching ferns. Based on an additional 11 transcriptomes of the same species, we identify unexpected variation in population-level heterozygosity.

genomics↗

bioRxiv2020

Emergence and diversification of a highly invasive chestnut pathogen lineage across south-eastern Europe

Invasive microbial species constitute a major threat to biodiversity, agricultural production and human health. Invasions are often dominated by one or a small number of genotypes, yet the underlying factors driving invasions are poorly understood. The chestnut blight fungus Cryphonectria parasitica first decimated the American chestnut and a recent outbreak threatens European chestnut trees. To unravel the mechanisms underpinning the invasion of south-eastern Europe, we sequenced 188 genomes of predominantly European strains. Genotypes outside of the invasion zone showed high levels of diversity with evidence for frequent and ongoing recombination. The invasive lineage emerged from the highly diverse European genotype pool rather than a secondary introduction from Asia. The expansion across south-eastern Europe was mostly clonal and is dominated by a single mating type suggesting a fitness advantage of asexual reproduction. Our findings show how an intermediary, highly diverse bridgehead population gave rise to an invasive, largely clonally expanding pathogen. Data availabilityAll raw sequencing data is available on the NCBI Short Read Archive (BioProject PRJNA604575)

evolutionary biology↗

bioRxiv2020

A population-level invasion by transposable elements in a fungal pathogen

AO_SCPLOWBSTRACTC_SCPLOWGenome evolution is driven by the activity of transposable elements (TEs). The spread of TEs can have deleterious effects including the destabilization of genome integrity and expansions. However, the precise triggers of genome expansions remain poorly understood because genome size evolution is typically investigated only among deeply divergent lineages. Here, we use a large population genomics dataset of 284 individuals from populations across the globe of Zymoseptoria tritici, a major fungal wheat pathogen. We built a robust map of genome-wide TE insertions and deletions to track a total of 2,456 polymorphic loci within the species. We show that purifying selection substantially depressed TE frequencies in most populations but some rare TEs have recently risen in frequency and likely confer benefits. We found that specific TE families have undergone a substantial genome-wide expansion from the pathogens center of origin to more recently founded populations. The most dramatic increase in TE insertions occurred between a pair of North American populations collected in the same field at an interval of 25 years. We find that both genome-wide counts of TE insertions and genome size have increased with colonization bottlenecks. Hence, the demographic history likely played a major role in shaping genome evolution within the species. We show that both the activation of specific TEs and relaxed purifying selection underpin this incipient expansion of the genome. Our study establishes a model to recapitulate TE-driven genome evolution over deeper evolutionary timescales.

genomics↗

bioRxiv2019

Genome compartmentalization predates species divergence in the plant pathogen genus Zymoseptoria

BackgroundAntagonistic co-evolution can drive rapid adaptation in pathogens and shape genome architecture. Comparative genome analyses of several fungal pathogens revealed highly variable genomes, for many species characterized by specific repeat-rich genome compartments with exceptionally high sequence variability. Dynamic genome architecture may enable fast adaptation to host genetics. The wheat pathogen Zymoseptoria tritici with its highly variable genome and has emerged as a model organism to study the genomic evolution of plant pathogens. Here, we compared genomes of Z. tritici isolates and genomes of sister species infecting wild grasses to address the evolution of genome composition and structure. ResultsUsing long-read technology, we sequenced and assembled genomes of Z. ardabiliae, Z. brevis, Z. pseudotritici and Z. passerinii, together with two isolates of Z. tritici. We report a high extent of genome collinearity among Zymoseptoria species and high conservation of genomic, transcriptomic and epigenomic signatures of compartmentalization. We identify high gene content variability both within and between species. In addition, such variability is mainly limited to the accessory chromosomes and accessory compartments. Despite strong host specificity and non-overlapping host-range between species, effectors are mainly shared among Zymoseptoria species, yet exhibiting a high level of presence-absence polymorphism within Z. tritici. Using in planta transcriptomic data from Z. tritici, we suggest different roles for the shared orthologs and for the accessory genes during infection of their hosts. ConclusionDespite previous reports of high genomic plasticity in Z. tritici, we describe here a high level of conservation in genomic, epigenomic and transcriptomic signatures of genome architecture and compartmentalization across the genus Zymoseptoria. The compartmentalized genome may reflect purifying selection to retain a functional core genome and relaxed selection on the accessory genome allowing a higher extent of polymorphism.

genomics↗

bioRxiv2019

A 19-isolate reference-quality global pangenome for the fungal wheat pathogen Zymoseptoria tritici

BackgroundThe gene content of a species largely governs its ecological interactions and adaptive potential. A species is therefore defined by both core genes shared between all individuals and accessory genes segregating presence-absence variation. There is growing evidence that eukaryotes, similar to bacteria, show intra-specific variability in gene content. However, it remains largely unknown how functionally relevant such a pangenome structure is for eukaryotes and what mechanisms underlie the emergence of highly polymorphic genome structures. ResultsHere, we establish a reference-quality pangenome of a fungal pathogen of wheat based on 19 complete genomes from isolates sampled across six continents. Zymoseptoria tritici causes substantial worldwide losses to wheat production due to rapidly evolved tolerance to fungicides and evasion of host resistance. We performed transcriptome-assisted annotations of each genome to construct a global pangenome. Major chromosomal rearrangements are segregating within the species and underlie extensive gene presence-absence variation. Conserved orthogroups account for only [~]60% of the species pangenome. Investigating gene functions, we find that the accessory genome is enriched for pathogenesis-related functions and encodes genes involved in metabolite production, host tissue degradation and manipulation of the immune system. De novo transposon annotation of the 19 complete genomes shows that the highly diverse chromosomal structure is tightly associated with transposable elements content. Furthermore, transposable element expansions likely underlie recent genome expansions within the species. ConclusionsTaken together, our work establishes a highly complex eukaryotic pangenome providing an unprecedented toolbox to study how pangenome structure impacts crop-pathogen interactions.

genomics↗

bioRxiv2019

Chromosomal assembly and analyses of genome-wide recombination rates in the forest pathogenic fungus Armillaria ostoyae

Recombination shapes the evolutionary trajectory of populations and plays an important role in the faithful transmission of chromosomes during meiosis. Levels of sexual reproduction and recombination are important properties of host-pathogen interactions because the speed of antagonistic co-evolution depends on the ability of hosts and pathogens to generate genetic variation. However, our understanding of the importance of recombination is limited because large taxonomic groups remain poorly investigated. Here, we analyze recombination rate variation in the basidiomycete fungus Armillaria ostoyae, which is an aggressive pathogen on a broad range of conifers and other trees. We constructed a dense genetic map using 198 single basidiospore progeny from a cross. Progeny were genotyped at a genome-wide set of single nucleotide polymorphism (SNP) markers using double digest restriction site associated DNA sequencing (ddRADseq). Based on a linkage map of on 11,700 SNPs spanning 1007.5 cM, we assembled genomic scaffolds into 11 putative chromosomes of a total genome size of 56.6 Mb. We identified 1984 crossover events among all progeny and found that recombination rates were highly variable along chromosomes. Recombination hotspots tended to be in regions close to the telomeres and were more gene-poor than the genomic background. Genes in proximity to recombination hotspots were encoding on average shorter proteins and were enriched for pectin degrading enzymes. Our analyses enable more powerful population and genome-scale studies of a major tree pathogen.

genomics↗

bioRxiv2019

A secreted LysM effector protects fungal hyphae through chitin-dependent homodimer polymerization

Plants trigger immune responses upon recognition of fungal cell wall chitin, followed by the release of various antimicrobials, including chitinase enzymes that hydrolyze chitin. In turn, many fungal pathogens secrete LysM effectors that prevent chitin recognition by the host through scavenging of chitin oligomers. We previously showed that intrachain LysM dimerization of the Cladosporium fulvum effector Ecp6 confers an ultrahigh-affinity binding groove that competitively sequesters chitin oligomers from host immune receptors. Additionally, particular LysM effectors are found to protect fungal hyphae against chitinase hydrolysis during host colonization. However, the molecular basis for the protection of fungal cell walls against hydrolysis remained unclear. Here, we determined a crystal structure of the single LysM domain-containing effector Mg1LysM of the wheat pathogen Zymoseptoria tritici and reveal that Mg1LysM is involved in the formation of two kinds of dimers; a chitin-dependent dimer as well as a chitin-independent homodimer. In this manner, Mg1LysM gains the capacity to form a supramolecular structure by chitin-induced oligomerization of chitin-independent Mg1LysM homodimers, a property that confers protection to fungal cell walls against host chitinases.

microbiology↗

bioRxiv2019

Complex evolutionary origins of specialized metabolite gene cluster diversity among the plant pathogenic fungi of the Fusarium graminearum species complex

Fungal genomes encode highly organized gene clusters that underlie the production of specialized (or secondary) metabolites. Gene clusters encode key functions to exploit plant hosts or environmental niches. Promiscuous exchange among species and frequent reconfigurations make gene clusters some of the most dynamic elements of fungal genomes. Despite evidence for high diversity in gene cluster content among closely related strains, the microevolutionary processes driving gene cluster gain, loss and neofunctionalization are largely unknown. We analyzed the Fusarium graminearum species complex (FGSC) composed of plant pathogens producing potent mycotoxins and causing Fusarium head blight on cereals. We de novo assembled genomes of previously uncharacterized FGSC members (two strains of F. austroamericanum, F. cortaderiae and F. meridionale). Our analyses of eight species of the FGSC in addition to 15 other Fusarium species identified a pangenome of 54 gene clusters within FGSC. We found that multiple independent losses were a key factor generating extant cluster diversity within the FGSC and the Fusarium genus. We identified a modular gene cluster conserved among distantly related fungi, which was likely reconfigured to encode different functions. We also found strong evidence that a rare cluster in FGSC was gained through an ancient horizontal transfer between bacteria and fungi. Chromosomal rearrangements underlying cluster loss were often complex and were likely facilitated by an enrichment in specific transposable elements. Our findings identify important transitory stages in the birth and death process of specialized metabolism gene clusters among very closely related species.

genomics↗

bioRxiv2019

Stress-driven transposable element de-repression dynamics in a fungal pathogen

Transposable elements (TEs) are drivers of genome evolution and affect the expression landscape of the host genome. Stress is a major factor inducing TE activity, however the regulatory mechanisms underlying de-repression are poorly understood. Key unresolved questions are whether different types of stress differentially induce TE activity and whether different TEs respond differently to the same stress. Plant pathogens are excellent models to dissect the impact of stress on TEs, because lifestyle transitions on and off the host impose exposure to a variety of stress conditions. We analyzed the TE expression landscape of four well-characterized strains of the major wheat pathogen Zymoseptoria tritici. We experimentally exposed strains to nutrient starvation and host infection stress. Contrary to expectations, we show that the two distinct conditions induce the expression of different sets of TEs. In particular, the most highly expressed TEs, including MITE and LTR-Gypsy elements, show highly distinct de-repression across stress conditions. Both the genomic context of TEs and the genetic background stress (i.e. different strains harboring the same TEs) were major predictors of de-repression dynamics under stress. Genomic defenses inducing point mutations in repetitive regions were largely ineffective to prevent TE de-repression. Consistent with TE de-repression being governed by epigenetic effects, we found that gene expression profiles under stress varied significantly depending on the proximity to the closest TEs. The unexpected complexity in TE responsiveness to stress across genetic backgrounds and genomic locations shows that species harbor substantial genetic variation to control TEs.

genomics↗

bioRxiv2019

Accumulation and purging of deleterious mutations through severe bottlenecks in ibex

Human activity caused dramatic population declines in many wild species. The resulting bottlenecks have a profound impact on the genetic makeup of a species with unknown consequences for health. A key genetic factor for species survival is the evolution of deleterious mutation load, but how bottleneck strength and mutation load interact lacks empirical evidence. Here, we take advantage of the exceptionally well-characterized population bottlenecks of the once nearly extinct Alpine ibex. The species survived one of the most dramatic bottlenecks known for successfully restored species. We analyze 60 complete genomes of six ibex species and the domestic goat. We show that historic bottlenecks rather than the current conservation status predict levels of genome-wide variation. By retracing the recolonization of the Alps by Alpine ibex, we find genomic evidence of concurrent purging of highly deleterious mutations but accumulation of mildly deleterious mutations. This demonstrates how human-induced severe bottlenecks caused both relaxed selection and purging, thus reshaping the landscape of deleterious mutation load. Our findings also highlight that even populations of ~1000 individuals can accumulate mildly deleterious mutations. Hence, conservation efforts should focus on preventing population declines below such levels to ensure long-term survival of species.

evolutionary biology↗

bioRxiv2018

The monothiol glutaredoxin Grx4 interacts with the Cryptococcus iron regulator Cir1 and regulates iron homeostasis and virulence in the Cryptococcus neoformans

The acquisition of iron and the maintenance of iron homeostasis are important aspects of the virulence in the pathogenic fungus Cryptococcus neoformans. In this study, we identified the monothiol glutaredoxin Grx4 as a binding partner of Cir1, a master regulator of iron-responsive genes and virulence factor elaboration in C. neoformans. Monothiol glutaredoxins are important regulators of iron homeostasis because of their conserved roles in [2Fe-2S] cluster sensing and trafficking. We confirmed that Grx4 binds Cir1 and demonstrated that iron repletion promotes the relocalization of Grx4 from the nucleus to the cytoplasm. Nuclear retention is partially dependent on Cir1 and also influenced by treatment with the proteasome inhibitor bortezomib. Cir1 remains in the nucleus in both iron replete and iron limiting conditions. We also found that a grx4{Delta} mutant displayed iron-related phenotypes similar to those of a cir1{Delta} mutant, including poor growth upon iron deprivation. Importantly, a grx4{Delta} mutant was avirulent in mice, a phenotype consistent with observed defects in the key virulence determinants, capsule and melanin, and poor growth at 37{degrees}C. A comparative transcriptome analysis of a grx4{Delta} mutant and the WT strain in low iron and iron-replete conditions confirmed a central role for Grx4 in iron homeostasis. Dysregulation of iron-related metabolism was consistent with grx4{Delta} mutant phenotypes related to oxidative stress, mitochondrial function, and DNA repair. Overall, the phenotypes of the grx4{Delta} mutant and the RNA-Seq analysis support the hypothesis that Grx4 functions as a sensor of iron levels, in part through an interaction with Cir1, to extensively regulate iron homeostasis and contribute to virulence.

microbiology↗