Functional characterization of the putative Aspergillus nidulans poly(ADP-ribose) polymerase homolog PrpA

Poly(ADP-ribose) polymerase FonPARP1-catalyzed PARylation of protein disulfide isomerase FonPdi1 regulates pathogenicity of Fusarium oxysporum f. sp. niveum on watermelon

Poly(ADP-ribosyl)ation (PARylation), catalyzed by poly(ADP-ribose) polymerases (PARPs) and hydrolyzed by poly(ADP-ribose) glycohydrolase (PARG), is an important reversible post-translational protein modification in all eukaryotes, including plant pathogenic fungi. Previously, we revealed that FonPARP1, an active PARP, is crucial for the pathogenicity of Fusarium oxysporum f. sp. niveum (Fon), the causative agent of watermelon Fusarium wilt. This study explores the enzymatic activity and substrates of FonPARP1 in regulating Fon pathogenicity. FonPARP1 is localized in nuclei of Fon macroconidia and hyphae. Essential conserved domains and a key glutamic acid residue at position 729 are critical for FonPARP1 enzyme activity and pathogenicity function in Fon. FonPARP1 interacts with protein disulfide isomerase FonPdi1 and PARylates it at 13 glutamic acid residues, affecting the interaction ability, PDI activity, ER homeostasis, and pathogenicity function. FonPARG1, interacting with both FonPARP1 and FonPdi1, hydrolyzes poly(ADP-ribose) chains from auto-PARylated FonPARP1 and FonPARP1-PARylated FonPdi1. These findings underscore the role of FonPARP1-catalyzed PARylation in regulating Fon pathogenicity and its significance in plant pathogenic fungi.

Poly ADP-Ribosylation in a Plant Pathogenic Oomycete Phytophthora infestans: A Key Controller of Growth and Host Plant Colonisation

ADP-ribosylation is a reversible modification of proteins and nucleic acids, which controls major cellular processes, including DNA damage repair, cell proliferation and differentiation, metabolism, stress, and immunity in plants and animals. The involvement of ADP-ribosylation in the life cycle of Dictyostelium and some filamentous fungi has also been demonstrated. However, the role of this process in pathogenic oomycetes has never been addressed. Here, we show that the Phytophthora infestans genome contains two PARP-like protein genes (PiPARP1 and PiPARP2), and provide evidence of PARylation activity for one of them (PiPARP2). Using dsRNA-mediated RNA silencing of the PiPARP2 gene and chemical (pharmacological) inhibition of PARP activity by 3-aminobenzamide (3AB) PARP inhibitor, we demonstrate the critical functional role of ADP-ribosylation in Phytophthora mycelium growth. Virulence test on detached leaves also suggests an important role of ADP-ribosylation in Phytophthora host plant colonisation and pathogenesis. On a practical level, our data suggest that targeting the PARylation system may constitute a novel powerful approach for the management of Phytophthora diseases.

Protein PARylation: a novel regulator of fungal virulence

Protein PARylation is a reversible post-translational modification; however, its role in fungal virulence has remained elusive. Recently, Gao et al. demonstrated that PARylation of two 14-3-3 regulatory proteins by poly(ADP-ribose) polymerase is essential for the virulence of rice blast fungus, highlighting the critical regulatory function of PARylation in fungal pathogenicity.

Investigating the Structure of the Components of the PolyADP-Ribosylation System in Fusarium Fungi and Evaluating the Expression Dynamics of Its Key Genes

Poly(ADP-ribose) polymerase (PARP) is the key enzyme in polyADP-ribosylation, one of the main post-translational modifications. This enzyme is abundant in eukaryotic organisms. However, information on the PARP structure and its functions in members of the Fungi kingdom is very limited. In this study, we performed a bioinformatic search for homologs of PARP and its antagonist, PARG, in the genomes of four Fusarium strains using their whole-genome sequences annotated and deposited in databases. The F. graminearum PH-1, F. proliferatum ET-1, and F. oxysporum Fo47 strains were shown to possess a single homolog of both PARP and PARG. In addition, the F. oxysporum f. sp. lycopersici strain 4287 contained four additional proteins comprising PARP catalytic domains whose structure was different from that of the remaining identified homologs. Partial nucleotide sequences encoding the catalytic domains of the PARP and PARG homologs were determined in 11 strains of 9 Fusarium species deposited in all-Russian collections, and the phylogenetic properties of the analyzed genes were evaluated. In the toxigenic F. graminearum strain, we demonstrated up-regulation of the gene encoding the PARP homolog upon culturing under conditions stimulating the production of the DON mycotoxin, as well as up-regulation of the gene encoding PARG at later stages of growth. These findings indirectly indicate involvement of the polyADP-ribosylation system in the regulation of the genes responsible for DON biosynthesis.

Cellular ATP redistribution achieved by deleting Tgparp improves lignocellulose utilization of Trichoderma under heat stress

BACKGROUND

Thermotolerance is widely acknowledged as a pivotal factor for fungal survival across diverse habitats. Heat stress induces a cascade of disruptions in various life processes, especially in the acquisition of carbon sources, while the mechanisms by which filamentous fungi adapt to heat stress and maintain carbon sources are still not fully understood.

RESULTS

Using Trichoderma guizhouense, a representative beneficial microorganism for plants, we discover that heat stress severely inhibits the lignocellulases secretion, affecting carbon source utilization efficiency. Proteomic results at different temperatures suggest that proteins involved in the poly ADP-ribosylation pathway (TgPARP and TgADPRase) may play pivotal roles in thermal adaptation and lignocellulose utilization. TgPARP is induced by heat stress, while the deletion of Tgparp significantly improves the lignocellulose utilization capacity and lignocellulases secretion in T. guizhouense. Simultaneously, the absence of Tgparp prevents the excessive depletion of ATP and NAD+, enhances the protective role of mitochondrial membrane potential (MMP), and elevates the expression levels of the unfolded protein response (UPR)-related regulatory factor Tgire. Further investigations reveal that a stable MMP can establish energy homeostasis, allocating more ATP within the endoplasmic reticulum (ER) to reduce protein accumulation in the ER, thereby enhancing the lignocellulases secretion in T. guizhouense under heat stress.

CONCLUSIONS

Overall, these findings underscored the significance of Tgparp as pivotal regulators in lignocellulose utilization under heat stress and provided further insights into the molecular mechanism of filamentous fungi in utilizing lignocellulose.

The Ser/Thr protein kinase FonKin4-poly(ADP-ribose) polymerase FonPARP1 phosphorylation cascade is required for the pathogenicity of watermelon fusarium wilt fungus Fusarium oxysporum f. sp. niveum

Poly(ADP-ribosyl)ation (PARylation), catalyzed by poly(ADP-ribose) polymerases (PARPs) and hydrolyzed by poly(ADP-ribose) glycohydrolase (PARG), is a kind of post-translational protein modification that is involved in various cellular processes in fungi, plants, and mammals. However, the function of PARPs in plant pathogenic fungi remains unknown. The present study investigated the roles and mechanisms of FonPARP1 in watermelon Fusarium wilt fungus Fusarium oxysporum f. sp. niveum (Fon). Fon has a single PARP FonPARP1 and one PARG FonPARG1. FonPARP1 is an active PARP and contributes to Fon pathogenicity through regulating its invasive growth within watermelon plants, while FonPARG1 is not required for Fon pathogenicity. A serine/threonine protein kinase, FonKin4, was identified as a FonPARP1-interacting partner by LC-MS/MS. FonKin4 is required for vegetative growth, conidiation, macroconidia morphology, abiotic stress response and pathogenicity of Fon. The S_TKc domain is sufficient for both enzyme activity and pathogenicity function of FonKin4 in Fon. FonKin4 phosphorylates FonPARP1 in vitro to enhance its poly(ADP-ribose) polymerase activity; however, FonPARP1 does not PARylate FonKin4. These results establish the FonKin4-FonPARP1 phosphorylation cascade that positively contributes to Fon pathogenicity. The present study highlights the importance of PARP-catalyzed protein PARylation in regulating the pathogenicity of Fon and other plant pathogenic fungi.

The contribution of DNA repair pathways to genome editing and evolution in filamentous pathogens

DNA double-strand breaks require repair or risk corrupting the language of life. To ensure genome integrity and viability, multiple DNA double-strand break repair pathways function in eukaryotes. Two such repair pathways, canonical non-homologous end joining and homologous recombination, have been extensively studied, while other pathways such as microhomology-mediated end joint and single-strand annealing, once thought to serve as back-ups, now appear to play a fundamental role in DNA repair. Here, we review the molecular details and hierarchy of these four DNA repair pathways, and where possible, a comparison for what is known between animal and fungal models. We address the factors contributing to break repair pathway choice, and aim to explore our understanding and knowledge gaps regarding mechanisms and regulation in filamentous pathogens. We additionally discuss how DNA double-strand break repair pathways influence genome engineering results, including unexpected mutation outcomes. Finally, we review the concept of biased genome evolution in filamentous pathogens, and provide a model, termed Biased Variation, that links DNA double-strand break repair pathways with properties of genome evolution. Despite our extensive knowledge for this universal process, there remain many unanswered questions, for which the answers may improve genome engineering and our understanding of genome evolution.

A Special Phenotype of Aconidial Aspergillus niger SH2 and Its Mechanism of Formation via CRISPRi

The complex morphological structure of Aspergillus niger influences its production of proteins, metabolites, etc., making the genetic manipulation and clonal purification of this species increasingly difficult, especially in aconidial Aspergillus niger. In this study, we found that N-acetyl-D-glucosamine (GlcNAc) could induce the formation of spore-like propagules in the aconidial Aspergillus niger SH2 strain. The spore-like propagules possessed life activities such as drug resistance, genetic transformation, and germination. Transcriptomic analysis indicated that the spore-like propagules were resting conidia entering dormancy and becoming more tolerant to environmental stresses. The Dac1 gene and the metabolic pathway of GlcNAc converted to glycolysis are related to the formation of the spore-like propagules, as evidenced by the CRISPRi system, qPCR, and semi-quantitative RT-PCR. Moreover, a method based on the CRISPR-Cas9 tool to rapidly recycle screening tags and recover genes was suitable for Aspergillus niger SH2. To sum up, this suggests that the spore-like propagules are resting conidia and the mechanism of their formation is the metabolic pathway of GlcNAc converted to glycolysis, particularly the Dac1 gene. This study can improve our understanding of the critical factors involved in mechanisms of phenotypic change and provides a good model for researching phenotypic change in filamentous fungi.

Identification and characterization of Poly(ADP-ribose) polymerase-1 interacting proteins during development of Dictyostelium discoideum

Poly (ADP-ribose) polymerase-1 (PARP-1) is a multifunctional protein that is associated with various biological processes like chromatin remodeling, DNA damage, cell death etc. In Dictyostelium discoideum, PARP-1 has also been implicated in cellular differentiation and development. However, its interacting proteins during multicellular development are not yet explored. Hence, the present study aims to identify PARP-1 interacting proteins during multicellular development of D. discoideum. BRCA1 C-terminus (BRCT) domain of PARP-1, which is mainly involved in protein-protein interactions was cloned in pGEX4T1 vector and developmental interactome of PARP-1 were analyzed by affinity purification-mass spectrometry. These interactions were further confirmed by in-silico protein-protein docking analysis, which led to identification of the proteins that show high affinity for BRCT domain. Initially, the protein structures were modeled on SWISS MODEL and PHYRE2 servers, refined by 3Drefine and validated by PROCHECK. Further, interaction sites of BRCT and the conserved regions in all interacting proteins were predicted using cons-PPISP and ConSurf, respectively. Finally, protein-protein docking analysis was done by HADDOCK. Our results identified 19 possible BRCT interacting proteins during D. discoideum development. Furthermore, interacting residues involved in the interactions and functional regions were explored. This is the first report where PARP-1's developmental interactome in D. discoideum is well established. The current findings demonstrate PARP-1's developmental interactome in D. discoideum and provide the groundwork to understand its regulated functions in developmental biology which would undoubtedly extend our perception towards developmental diseases in higher complex organisms and their treatment.

Fungal G-Protein-Coupled Receptors: A Promising Mediator of the Impact of Extracellular Signals on Biosynthesis of Ochratoxin A

G-protein-coupled receptors (GPCRs) are transmembrane receptors involved in transducing signals from the external environment inside the cell, which enables fungi to coordinate cell transport, metabolism, and growth to promote their survival, reproduction, and virulence. There are 14 classes of GPCRs in fungi involved in sensing various ligands. In this paper, the synthesis of mycotoxins that are GPCR-mediated is discussed with respect to ligands, environmental stimuli, and intra-/interspecific communication. Despite their apparent importance in fungal biology, very little is known about the role of ochratoxin A (OTA) biosynthesis by Aspergillus ochraceus and the ligands that are involved. Fortunately, increasing evidence shows that the GPCR that involves the AF/ST (sterigmatocystin) pathway in fungi belongs to the same genus. Therefore, we speculate that GPCRs play an important role in a variety of environmental signals and downstream pathways in OTA biosynthesis. The verification of this inference will result in a more controllable GPCR target for control of fungal contamination in the future.

Mechanistic insight into the role of Poly(ADP-ribosyl)ation in DNA topology modulation and response to DNA damage

Genotoxic stress generates single- and double-strand DNA breaks either through direct damage by reactive oxygen species or as intermediates of DNA repair. Failure to detect and repair DNA strand breaks leads to deleterious consequences such as chromosomal aberrations, genomic instability and cell death. DNA strand breaks disrupt the superhelical state of cellular DNA, which further disturbs the chromatin architecture and gene activity regulation. Proteins from the poly(ADP-ribose) polymerase (PARP) family, such as PARP1 and PARP2, use NAD+ as a substrate to catalyse the synthesis of polymeric chains consisting of ADP-ribose units covalently attached to an acceptor molecule. PARP1 and PARP2 are regarded as DNA damage sensors that, upon activation by strand breaks, poly(ADP-ribosyl)ate themselves and nuclear acceptor proteins. Noteworthy, the regularly branched structure of poly(ADP-ribose) polymer suggests that the mechanism of its synthesis may involve circular movement of PARP1 around the DNA helix, with a branching point in PAR corresponding to one complete 360° turn. We propose that PARP1 stays bound to a DNA strand break end, but rotates around the helix displaced by the growing poly(ADP-ribose) chain, and that this rotation could introduce positive supercoils into damaged chromosomal DNA. This topology modulation would enable nucleosome displacement and chromatin decondensation around the lesion site, facilitating the access of DNA repair proteins or transcription factors. PARP1-mediated DNA supercoiling can be transmitted over long distances, resulting in changes in the high-order chromatin structures. The available structures of PARP1 are consistent with the strand break-induced PAR synthesis as a driving force for PARP1 rotation around the DNA axis.

The Role of PARPs in Inflammation-and Metabolic-Related Diseases: Molecular Mechanisms and Beyond

Poly(ADP-ribosyl)ation (PARylation) is an essential post-translational modification catalyzed by poly(ADP-ribose) polymerase (PARP) enzymes. Poly(ADP-ribose) polymerase 1 (PARP1) is a well-characterized member of the PARP family. PARP1 plays a crucial role in multiple biological processes and PARP1 activation contributes to the development of various inflammatory and malignant disorders, including lung inflammatory disorders, cardiovascular disease, ovarian cancer, breast cancer, and diabetes. In this review, we will focus on the role and molecular mechanisms of PARPs enzymes in inflammation- and metabolic-related diseases. Specifically, we discuss the molecular mechanisms and signaling pathways that PARP1 is associated with in the regulation of pathogenesis. Recently, increasing evidence suggests that PARP inhibition is a promising strategy for intervention of some diseases. Thus, our in-depth understanding of the mechanism of how PARPs are activated and how their signaling downstream effecters can provide more potential therapeutic targets for the treatment of the related diseases in the future is crucial.

Novel insights into PARPs in gene expression: regulation of RNA metabolism

Poly(ADP-ribosyl)ation (PARylation) is an important post-translational modification in which an ADP-ribose group is transferred to the target protein by poly(ADP-riboses) polymerases (PARPs). Since the discovery of poly-ADP-ribose (PAR) 50 years ago, its roles in cellular processes have been extensively explored. Although research initially focused on the functions of PAR and PARPs in DNA damage detection and repair, our understanding of the roles of PARPs in various nuclear and cytoplasmic processes, particularly in gene expression, has increased significantly. In this review, we discuss the current advances in understanding the roles of PARylation with a particular emphasis in gene expression through RNA biogenesis and processing. In addition to updating PARP's significance in transcriptional regulation, we specifically focus on how PARPs and PARylation affect gene expression, especially inflammation-related genes, at the post-transcriptional levels by modulating RNA processing and degrading. Increasing evidence suggests that PARP inhibition is a promising treatment for inflammation-related diseases besides conventional chemotherapy for cancer.

Metabolic Profiling of Water-Soluble Compounds from the Extracts of Dark Septate Endophytic Fungi (DSE) Isolated from Scots Pine (Pinus sylvestris L.) Seedlings Using UPLC-Orbitrap-MS

Endophytes are microorganisms living inside plant hosts and are known to be beneficial for the host plant vitality. In this study, we isolated three endophytic fungus species from the roots of Scots pine seedlings growing on Finnish drained peatland setting. The isolated fungi belonged to dark septate endophytes (DSE). The metabolic profiles of the hot water extracts of the fungi were investigated using Ultrahigh Performance Liquid Chromatography with Diode Array Detection and Electron Spray Ionization source Mass Spectrometry with Orbitrap analyzer (UPLC-DAD-ESI-MS-Orbitrap). Out of 318 metabolites, we were able to identify 220, of which a majority was amino acids and peptides. Additionally, opine amino acids, amino acid quinones, Amadori compounds, cholines, nucleobases, nucleosides, nucleotides, siderophores, sugars, sugar alcohols and disaccharides were found, as well as other previously reported metabolites from plants or endophytes. Some differences of the metabolic profiles, regarding the amount and identity of the found metabolites, were observed even though the fungi were isolated from the same host. Many of the discovered metabolites have been described possessing biological activities and properties, which may make a favorable contribution to the host plant nutrient availability or abiotic and biotic stress tolerance.

Poly(ADP-ribose) polymerase-1 (PARP-1) regulates developmental morphogenesis and chemotaxis in Dictyostelium discoideum

BACKGROUND INFORMATION

Poly(ADP-ribose) polymerase-1 (PARP-1) has been attributed to varied roles in DNA repair, cell cycle, cell death, etc. Our previous reports demonstrate the role of PARP-1 during Dictyostelium discoideum development by its constitutive downregulation as well as by PARP-1 ortholog, ADP ribosyl transferase 1 A (ADPRT1A) overexpression. The current study analyses and strengthens the function of ADPRT1A in multicellular morphogenesis of D. discoideum. ADPRT1A was knocked out, and its effect was studied on cAMP signalling, chemotaxis and development of D. discoideum.

RESULTS

We report that ADPRT1A is essential in multicellular development of D. discoideum, particularly at the aggregation stage. Genetic alterations of ADPRT1A and chemical inhibition of its activity affects the intracellular and extracellular cAMP levels during aggregation along with chemotaxis. Exogenous cAMP pulses could rescue this defect in the ADPRT1A knockout (ADPRT1A KO). Expression analysis of genes involved in cAMP signalling reveals altered transcript levels of four essential genes (PDSA, REGA, ACAA and CARA). Moreover, ADPRT1A KO affects prespore- and prestalk-specific gene expression and prestalk tendency is favoured in the ADPRT1A KO.

CONCLUSION

ADPRT1A plays a definite role in regulating developmental morphogenesis via cAMP signalling.

SIGNIFICANCE

This study helps in understanding the role of PARP-1 in multicellular development and differentiation in higher complex organisms.

Programmed cell death in human pathogenic fungi - a possible therapeutic target

INTRODUCTION

Diseases caused by pathogenic fungi are increasing because of antibiotic overuse, the rise of immunosuppressive therapies, and climate change. The limited variety of antimycotics and the rapid adaptation of pathogenic fungi to antifungal agents serve to exacerbate this issue. Unfortunately, about 1.6 million people are killed by fungal infections annually. Areas covered: The discovery of the small antimicrobial proteins produced by microorganisms, animals, humans, and plants will hopefully overcome challenges in the treatment of fungal infections. These small proteins are highly stable and any resistance to them rarely evolves; therefore, they are potentially good candidates for the treatment and prevention of infections caused by pathogenic fungi. Some of these proteins target the programmed cell death machinery of pathogenic fungi; this is potentially a novel approach in antimycotic therapies. In this review, we highlight the elements of apoptosis in human pathogenic fungi and related model organisms and discuss the possible therapeutic potential of the apoptosis-inducing, small, antifungal proteins. Expert opinion: Small antimicrobial proteins may establish a new class of antimycotics in the future. The rarity of resistance and their synergistic effects with other frequently used antifungal agents may help pave the way for their use in the clinic.

Regulated Forms of Cell Death in Fungi

Cell death occurs in all domains of life. While some cells die in an uncontrolled way due to exposure to external cues, other cells die in a regulated manner as part of a genetically encoded developmental program. Like other eukaryotic species, fungi undergo programmed cell death (PCD) in response to various triggers. For example, exposure to external stress conditions can activate PCD pathways in fungi. Calcium redistribution between the extracellular space, the cytoplasm and intracellular storage organelles appears to be pivotal for this kind of cell death. PCD is also part of the fungal life cycle, in which it occurs during sexual and asexual reproduction, aging, and as part of development associated with infection in phytopathogenic fungi. Additionally, a fungal non-self-recognition mechanism termed heterokaryon incompatibility (HI) also involves PCD. Some of the molecular players mediating PCD during HI show remarkable similarities to major constituents involved in innate immunity in metazoans and plants. In this review we discuss recent research on fungal PCD mechanisms in comparison to more characterized mechanisms in metazoans. We highlight the role of PCD in fungi in response to exogenic compounds, fungal development and non-self-recognition processes and discuss identified intracellular signaling pathways and molecules that regulate fungal PCD.

Poly ADP-ribose polymerase-1: Beyond transcription and towards differentiation

Gene regulation mediates the processes of cellular development and differentiation leading to the origin of different cell types each having their own signature gene expression profile. However, the compact chromatin structure and the timely recruitment of molecules involved in various signaling pathways are of prime importance for temporal and spatial gene regulation that eventually contribute towards cell type and specificity. Poly (ADP-ribose) polymerase-1 (PARP-1), a 116-kDa nuclear multitasking protein is involved in modulation of chromatin condensation leading to altered gene expression. In response to activation signals, it adds ADP-ribose units to various target proteins including itself, thus regulating various key cellular processes like DNA repair, cell death, transcription, mRNA splicing etc. This review provides insights into the role of PARP-1 in gene regulation, cell differentiation and multicellular morphogenesis. In addition, the review also explores involvement of PARP-1 in immune cells development and therapeutic possibilities to treat various human diseases.

The PARP family: insights into functional aspects of poly (ADP-ribose) polymerase-1 in cell growth and survival

PARP family members can be found spread across all domains and continue to be essential molecules from lower to higher eukaryotes. Poly (ADP-ribose) polymerase 1 (PARP-1), newly termed ADP-ribosyltransferase D-type 1 (ARTD1), is a ubiquitously expressed ADP-ribosyltransferase (ART) enzyme involved in key cellular processes such as DNA repair and cell death. This review assesses current developments in PARP-1 biology and activation signals for PARP-1, other than conventional DNA damage activation. Moreover, many essential functions of PARP-1 still remain elusive. PARP-1 is found to be involved in a myriad of cellular events via conservation of genomic integrity, chromatin dynamics and transcriptional regulation. This article briefly focuses on its other equally important overlooked functions during growth, metabolic regulation, spermatogenesis, embryogenesis, epigenetics and differentiation. Understanding the role of PARP-1, its multidimensional regulatory mechanisms in the cell and its dysregulation resulting in diseased states, will help in harnessing its true therapeutic potential.

Poly (ADP-ribose) polymerase1 regulates growth and multicellularity in D. discoideum

Poly (ADP-ribose) polymerase (PARP)-1 regulates various biological processes like DNA repair, cell death etc. However, the role of PARP-1 in growth and differentiation still remains elusive. The present study has been undertaken to understand the role of PARP-1 in growth and development of a unicellular eukaryote, Dictyostelium discoideum. In silico analysis demonstrates ADPRT1A as the ortholog of human PARP-1 in D. discoideum. The present study shows that ADPRT1A overexpression (A OE) led to slow growth of D. discoideum and significant population of AOE cells were in S and G2/M phase. Also, AOE cells exhibited high endogenous PARP activity, significant NAD(+) depletion and also significantly lower ADPRT1B and ADPRT2 transcript levels. Moreover, AOE cells are intrinsically stressed and also exhibited susceptibility to oxidative stress. AOE also affected development of D. discoideum predominantly streaming, aggregation and formation of early culminant which are concomitant with reports on PARP's role in D. discoideum development. In addition, under developmental stimuli, increased PARP activity was seen along with developmentally regulated transcript levels of ADPRT1A during D. discoideum multicellularity. Thus the present study suggests that PARP-1 regulates growth as well as the developmental morphogenesis of D. discoideum, thereby opening new avenues to understand the same in higher eukaryotes.

Distribution of protein poly(ADP-ribosyl)ation systems across all domains of life

Poly(ADP-ribosyl)ation is a post-translational modification of proteins involved in regulation of many cellular pathways. Poly(ADP-ribose) (PAR) consists of chains of repeating ADP-ribose nucleotide units and is synthesized by the family of enzymes called poly(ADP-ribose) polymerases (PARPs). This modification can be removed by the hydrolytic action of poly(ADP-ribose) glycohydrolase (PARG) and ADP-ribosylhydrolase 3 (ARH3). Hydrolytic activity of macrodomain proteins (MacroD1, MacroD2 and TARG1) is responsible for the removal of terminal ADP-ribose unit and for complete reversion of protein ADP-ribosylation. Poly(ADP-ribosyl)ation is widely utilized in eukaryotes and PARPs are present in representatives from all six major eukaryotic supergroups, with only a small number of eukaryotic species that do not possess PARP genes. The last common ancestor of all eukaryotes possessed at least five types of PARP proteins that include both mono and poly(ADP-ribosyl) transferases. Distribution of PARGs strictly follows the distribution of PARP proteins in eukaryotic species. At least one of the macrodomain proteins that hydrolyse terminal ADP-ribose is also always present. Therefore, we can presume that the last common ancestor of all eukaryotes possessed a fully functional and reversible PAR metabolism and that PAR signalling provided the conditions essential for survival of the ancestral eukaryote in its ancient environment. PARP proteins are far less prevalent in bacteria and were probably gained through horizontal gene transfer. Only eleven bacterial species possess all proteins essential for a functional PAR metabolism, although it is not known whether PAR metabolism is truly functional in bacteria. Several dsDNA viruses also possess PARP homologues, while no PARP proteins have been identified in any archaeal genome. Our analysis of the distribution of enzymes involved in PAR metabolism provides insight into the evolution of these important signalling systems, as well as providing the basis for selection of the appropriate genetic model organisms to study the physiology of the specific human PARP proteins.

Conformational activation of poly(ADP-ribose) polymerase-1 upon DNA binding revealed by small-angle X-ray scattering

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear protein that plays key roles in several fundamental cellular processes. PARP-1 catalyzes the polymerization of nicotinamide adenine dinucleotide on itself and other acceptor proteins, forming long branched poly(ADP-ribose) polymers. The catalytic activity of PARP-1 is stimulated upon binding to damaged DNA, but how this signal is transmitted from the N-terminal DNA binding domain to the C-terminal catalytic domain in the context of the full-length enzyme is unknown. In this paper, small-angle X-ray scattering experiments and molecular dynamics simulations were used to gain insight into the conformational changes that occur during the catalytic activation of PARP-1 by an 8-mer DNA ligand. The data are consistent with a model in which binding of the DNA ligand establishes interdomain interactions between the DNA binding and catalytic domains, which induces an allosteric change in the active site that promotes catalysis. Moreover, the PARP-1-8-mer complex is seen to adopt a conformation that is poised to recruit DNA repair factors to the site of DNA damage. This study provides the first structural information about the DNA-induced conformational activation of full-length PARP-1.

A Nudix Hydrolase Protein, Ysa1, Regulates Oxidative Stress Response and Antifungal Drug Susceptibility in Cryptococcus neoformans

A nucleoside diphosphate-linked moiety X (Nudix) hydrolase-like gene, YSA1, has been identified as one of the gromwell plant extract-responsive genes in Cryptococcus neoformans. Ysa1 is known to control intracellular concentrations of ADP-ribose or O-acetyl-ADP-ribose, and has diverse biological functions, including the response to oxidative stress in the ascomycete yeast, Saccharomyces cerevisiae. In this study, we characterized the role of YSA1 in the stress response and adaptation of the basidiomycete yeast, C. neoformans. We constructed three independent deletion mutants for YSA1, and analyzed their mutant phenotypes. We found that ysa1 mutants did not show increased sensitivity to reactive oxygen species-producing oxidative damage agents, such as hydrogen peroxide and menadione, but exhibited increased sensitivity to diamide, which is a thiol-specific oxidant. Ysa1 was dispensable for the response to most environmental stresses, such as genotoxic, osmotic, and endoplasmic reticulum stress. In conclusion, modulation of YSA1 may regulate the cellular response and adaptation of C. neoformans to certain oxidative stresses and contribute to the evolution of antifungal drug resistance.

The protein poly(ADP-ribosyl)ation system: its role in genome stability and lifespan determination

The processes that lead to violation of genome integrity are known to increase with age. This phenomenon is caused both by increased production of reactive oxygen species and a decline in the efficiency of antioxidant defense system as well as systems maintaining genome stability. Accumulation of different unrepairable genome damage with age may be the cause of many age-related diseases and the development of phenotypic and physiological signs of aging. It is also clear that there is a close connection between the mechanisms of the maintenance of genome stability, on one hand, and the processes of spontaneous tumor formation and lifespan, on the other. In this regard, the system of protein poly(ADP-ribosyl)ation activated in response to a variety of DNA damage seems to be of particular interest. Data accumulated to date suggest it to be a kind of focal point of cellular processes, guiding the path of cell survival or death depending on the degree of DNA damage. This review summarizes and analyzes data on the involvement of poly(ADP-ribosyl)ation in various mechanisms of DNA repair, its interaction with progeria proteins, and the possible role in the development of spontaneous tumors and lifespan determination. Special attention is given to the relationship between various polymorphisms of the human poly(ADP-ribose) polymerase-1 gene and longevity.

The recognition and removal of cellular poly(ADP-ribose) signals

Poly(ADP-ribosyl)ation is involved in the regulation of a variety of cellular pathways, including, but not limited to, transcription, chromatin, DNA damage and other stress signalling. Similar to other tightly regulated post-translational modifications, poly(ADP-ribosyl)ation employs 'writers', 'readers' and 'erasers' to confer regulatory functions. The generation of poly(ADP-ribose) is catalyzed by poly(ADP-ribose) polymerase enzymes, which use NAD(+) as a cofactor to sequentially transfer ADP-ribose units generating long polymers, which, in turn, can affect protein function or serve as a recruitment platform for additional factors. Historically, research has focused on poly(ADP-ribose) generation pathways, with knowledge about PAR recognition and degradation lagging behind. Over recent years, several discoveries have significantly furthered our understanding of poly(ADP-ribose) recognition and, even more so, of poly(ADP-ribose) degradation. In this review, we summarize current knowledge about the protein modules recognizing poly(ADP-ribose) and discuss the newest developments on the complete reversibility of poly(ADP-ribosyl)ation.

Transcriptome changes initiated by carbon starvation in Aspergillus nidulans

Carbon starvation is a common stress for micro-organisms both in nature and in industry. The carbon starvation stress response (CSSR) involves the regulation of several important processes including programmed cell death and reproduction of fungi, secondary metabolite production and extracellular hydrolase formation. To gain insight into the physiological events of CSSR, DNA microarray analyses supplemented with real-time RT-PCR (rRT-PCR) experiments on 99 selected genes were performed. These data demonstrated that carbon starvation induced very complex changes in the transcriptome. Several genes contributing to protein synthesis were upregulated together with genes involved in the unfolded protein stress response. The balance between biosynthesis and degradation moved towards degradation in the case of cell wall, carbohydrate, lipid and nitrogen metabolism, which was accompanied by the production of several hydrolytic enzymes and the induction of macroautophagy. These processes provide the cultures with long-term survival by liberating nutrients through degradation of the cell constituents. The induced synthesis of secondary metabolites, antifungal enzymes and proteins as well as bacterial cell wall-degrading enzymes demonstrated that carbon-starving fungi should have marked effects on the micro-organisms in their surroundings. Due to the increased production of extracellular and vacuolar enzymes during carbon starvation, the importance of the endoplasmic reticulum increased considerably.

Quorum sensing in fungi--a review

Quorum sensing (QS) is a mechanism of microbial communication dependent on cell density that can regulate several behaviors in bacteria such as secretion of virulence factors, biofilm formation, competence and bioluminescence. The existence of fungal QS systems was revealed ten years ago after the discovery that farnesol controls filamentation in the pathogenic polymorphic fungus Candida albicans. In the past decade, farnesol has been shown to play multiple roles in C. albicans physiology as a signaling molecule and inducing detrimental effects on host cells and other microbes. In addition to farnesol, the aromatic alcohol tyrosol was also found to be a C. albicans QS molecule (QSM) controlling growth, morphogenesis and biofilm formation. In Saccharomyces cerevisiae, two other aromatic alcohols, phenylethanol and tryptophol were found to be QSMs regulating morphogenesis during nitrogen starvation conditions. Additionally, population density-dependent behaviors that resemble QS have been described in several other fungal species. Although fungal QS research is still in its infancy, its discovery has changed our views about the fungal kingdom and could eventually lead to the development of new antifungal therapeutics.

Functions of the poly(ADP-ribose) polymerase superfamily in plants

Poly(ADP-ribosyl)ation is the covalent attachment of ADP-ribose subunits from NAD(+) to target proteins and was first described in plants in the 1970s. This post-translational modification is mediated by poly(ADP-ribose) polymerases (PARPs) and removed by poly(ADP-ribose) glycohydrolases (PARGs). PARPs have important functions in many biological processes including DNA repair, epigenetic regulation and transcription. However, these roles are not always associated with enzymatic activity. The PARP superfamily has been well studied in animals, but remains under-investigated in plants. Although plants lack the variety of PARP superfamily members found in mammals, they do encode three different types of PARP superfamily proteins, including a group of PARP-like proteins, the SRO family, that are plant specific. In plants, members of the PARP family and/or poly(ADP-ribosyl)ation have been linked to DNA repair, mitosis, innate immunity and stress responses. In addition, members of the SRO family have been shown to be necessary for normal sporophytic development. In this review, we summarize the current state of plant research into poly(ADP-ribosyl)ation and the PARP superfamily in plants.

The structure and catalytic mechanism of a poly(ADP-ribose) glycohydrolase

Posttranslational modification of proteins by poly(ADP-ribosyl)ation regulates many cellular pathways that are critical for genome stability, including DNA repair, chromatin structure, mitosis and apoptosis¹. Poly(ADP-ribose) (PAR) is composed of repeating ADP-ribose units linked via a unique glycosidic ribose-ribose bond, and is synthesised from NAD by poly(ADP-ribose) polymerases (PARPs)^1,2. Poly(ADP-ribose) glycohydrolase (PARG) is the only protein capable of specific hydrolysis of the ribose-ribose bonds present in PAR chains; its deficiency leads to cell death^3,4. Here we show that filamentous fungi and a number of bacteria possess a divergent form of PARG that exhibits all the main characteristics of the human PARG enzyme. We present the first PARG crystal structure (derived from the bacterium Thermomonospora curvata), which reveals that the PARG catalytic domain is a distant member of the ubiquitous ADP-ribose-binding macro domain family^5,6. High resolution structures of T. curvata PARG in complexes with ADP-ribose and the PARG inhibitor ADP-HPD, complemented by biochemical studies, allow us to propose a model for PAR binding and catalysis by PARG. Our insights into the PARG structure and catalytic mechanism should greatly improve our understanding of how PARG activity controls reversible protein poly(ADP-ribosyl)ation and potentially of how the defects in this regulation link to human disease.

Genetic dissection of PARylation in the filamentous fungus Neurospora crassa

PARylation is a posttranslational protein modification carried out by PAR polymerases (PARPs). These enzymes function as ADP-ribose transferases that add polymers of ADP-ribose (PAR) to target proteins. PARP proteins have critical functions impacting the aspects of normal human health, such as aging, as well as disease development, particularly cancer. Recently, the powerful antitumor PARP inhibitor Olaparib was shown to be effective in blocking the progression of BRCA1/2-associated tumors, prompting Bruce Alberts to call for an expansion of cancer research beyond utilization of cancer cell lines to include model organisms, such as bacteria, yeast, worms, flies, and mice. Although Dr. Alberts did not specifically mention the filamentous fungus Neurospora crassa, it is now known that Neurospora is the only genetically tractable model eukaryote with completely dispensable PARylation. PARylation in Neurospora can be entirely eliminated by disruption of a single predicted ORF, encoding a nuclear localized PARP protein termed Neurospora PARP ortholog (NPO). We, thus, present this initial genetic characterization of PARylation in N. crassa as evidence of the supreme advantage of using Neurospora as a tool for the genetic dissection of PARP and PARylation and emphasize the power of this system to advance unparalleled contributions to knowledge in this field.

Differential role of poly(ADP-ribose) polymerase in D. discoideum growth and development

BACKGROUND

Poly(ADP-ribose) polymerase is evolutionarily conserved as a responder to various forms of stress. Though PARP's role in cell death is well addressed, its role in development and multicellularity is still an enigma. We have previously reported the role of PARP in oxidative stress induced delayed development of D. discoideum.

RESULTS

In the current study we highlight the involvement of PARP during D. discoideum development. Oxidative stress affects expression of aca and cAR1 thus affecting aggregation. Although parp expression is not affected during oxidative stress but it is involved during normal development as confirmed by our PARP down-regulation studies. Constitutive PARP down-regulation resulted in blocked development while no effect was observed on D. discoideum growth. Interestingly, stage specific PARP down-regulation arrested development at the slug stage.

CONCLUSION

These results emphasize that PARP is essential for complex differentiation and its function may be linked to multicellularity. This is the first report where the involvement of PARP during normal multicellular development in D. discoideum, an ancient eukaryote, is established which could be of evolutionary significance. Thus our study adds one more role to the multitasking function of PARP.

The Aspergillus nidulans nucA(EndoG) homologue is not involved in cell death

Upon apoptosis induction, translocation of mammalian mitochondrial endonuclease G (EndoG) to the nucleus coincides with large-scale DNA fragmentation. Here, we describe for the first time a homologue of EndoG in filamentous fungi by investigating if the Aspergillus nidulans homologue of the EndoG gene, named nucA(EndoG), is being activated during farnesol-induced cell death. Our results suggest that NucA is not involved in cell death, but it plays a role in the DNA-damaging response in A. nidulans.

Evolutionary history of the poly(ADP-ribose) polymerase gene family in eukaryotes

BACKGROUND

The poly(ADP-ribose) polymerase (PARP) superfamily was originally identified as enzymes that catalyze the attachment of ADP-ribose subunits to target proteins using NAD+ as a substrate. The family is characterized by the catalytic site, termed the PARP signature. While these proteins can be found in a range of eukaryotes, they have been best studied in mammals. In these organisms, PARPs have key functions in DNA repair, genome integrity and epigenetic regulation. More recently it has been found that proteins within the PARP superfamily have altered catalytic sites, and have mono(ADP-ribose) transferase (mART) activity or are enzymatically inactive. These findings suggest that the PARP signature has a broader range of functions that initially predicted. In this study, we investigate the evolutionary history of PARP genes across the eukaryotes.

RESULTS

We identified in silico 236 PARP proteins from 77 species across five of the six eukaryotic supergroups. We performed extensive phylogenetic analyses of the identified PARPs. They are found in all eukaryotic supergroups for which sequence is available, but some individual lineages within supergroups have independently lost these genes. The PARP superfamily can be subdivided into six clades. Two of these clades were likely found in the last common eukaryotic ancestor. In addition, we have identified PARPs in organisms in which they have not previously been described.

CONCLUSIONS

Three main conclusions can be drawn from our study. First, the broad distribution and pattern of representation of PARP genes indicates that the ancestor of all extant eukaryotes encoded proteins of this type. Second, the ancestral PARP proteins had different functions and activities. One of these proteins was similar to human PARP1 and likely functioned in DNA damage response. The second of the ancestral PARPs had already evolved differences in its catalytic domain that suggest that these proteins may not have possessed poly(ADP-ribosyl)ation activity. Third, the diversity of the PARP superfamily is larger than previously documented, suggesting as more eukaryotic genomes become available, this gene family will grow in both number and type.

The roles played by Aspergillus nidulans apoptosis-inducing factor (AIF)-like mitochondrial oxidoreductase (AifA) and NADH-ubiquinone oxidoreductases (NdeA-B and NdiA) in farnesol resistance

Farnesol (FOH) is a nonsterol isoprenoid produced by dephosphorylation of farnesyl pyrophosphate, a catabolite of the cholesterol biosynthetic pathway. These isoprenoids inhibit proliferation and induce apoptosis. Here, we show that Aspergillus nidulans AifA encoding the apoptosis-inducing factor (AIF)-like mitochondrial oxidoreductase plays a role in the function of the mitochondrial Complex I. Additionally, we demonstrated that ndeA-B and ndiA encode external and internal alternative NADH dehydrogenases, respectively, that have a function in FOH resistance. When exposed to FOH, the ΔaifA and ΔndeA strains have increased ROS production while ΔndeB, ΔndeA ΔndeB, and ΔndiA mutant strains showed the same ROS accumulation than in the absence of FOH. We observed several compensatory mechanisms affecting the differential survival of these mutants to FOH.

PARP is involved in replicative aging in Neurospora crassa

Modification of proteins by the addition of poly(ADP-ribose) is carried out by poly(ADP-ribose) polymerases (PARPs). PARPs have been implicated in a wide range of biological processes in eukaryotes, but no universal function has been established. A study of the Aspergillus nidulans PARP ortholog (PrpA) revealed that the protein is essential and involved in DNA repair, reminiscent of findings using mammalian systems. We found that a Neurospora PARP orthologue (NPO) is dispensable for cell survival, DNA repair and epigenetic silencing but that replicative aging of mycelia is accelerated in an npo mutant strain. We propose that PARPs may control aging as proposed for Sirtuins, which also consume NAD+ and function either as mono(ADP-ribose) transferases or protein deacetylases. PARPs may regulate aging by impacting NAD+/NAM availability, thereby influencing Sirtuin activity, or they may function in alternative NAD+-dependent or NAD+-independent aging pathways.

Fungal apoptosis: function, genes and gene function

Cells of all living organisms are programmed to self-destruct under certain conditions. The most well known form of programmed cell death is apoptosis, which is essential for proper development in higher eukaryotes. In fungi, apoptotic-like cell death occurs naturally during aging and reproduction, and can be induced by environmental stresses and exposure to toxic metabolites. The core apoptotic machinery in fungi is similar to that in mammals, but the apoptotic network is less complex and of more ancient origin. Only some of the mammalian apoptosis-regulating proteins have fungal homologs, and the number of protein families is drastically reduced. Expression in fungi of animal proteins that do not have fungal homologs often affects apoptosis, suggesting functional conservation of these components despite the absence of protein-sequence similarity. Functional analysis of Saccharomyces cerevisiae apoptotic genes, and more recently of those in some filamentous species, has revealed partial conservation, along with substantial differences in function and mode of action between fungal and human proteins. It has been suggested that apoptotic proteins might be suitable targets for novel antifungal treatments. However, implementation of this approach requires a better understanding of fungal apoptotic networks and identification of the key proteins regulating apoptotic-like cell death in fungi.

Regulation of apical dominance in Aspergillus nidulans hyphae by reactive oxygen species

In fungal hyphae, apical dominance refers to the suppression of secondary polarity axes in the general vicinity of a growing hyphal tip. The mechanisms underlying apical dominance remain largely undefined, although calcium signaling may play a role. Here, we describe the localized accumulation of reactive oxygen species (ROS) in the apical region of Aspergillus nidulans hyphae. Our analysis of atmA (ATM) and prpA (PARP) mutants reveals a correlation between localized production of ROS and enforcement of apical dominance. We also provide evidence that NADPH oxidase (Nox) or related flavoproteins are responsible for the generation of ROS at hyphal tips and characterize the roles of the potential Nox regulators NoxR, Rac1, and Cdc42 in this process. Notably, our genetic analyses suggest that Rac1 activates Nox, whereas NoxR and Cdc42 may function together in a parallel pathway that regulates Nox localization. Moreover, the latter pathway may also include Bem1, which we propose represents a p40phox analog in fungi. Collectively, our results support a model whereby localized Nox activity generates a pool of ROS that defines a dominant polarity axis at hyphal tips.

Domain C of human poly(ADP-ribose) polymerase-1 is important for enzyme activity and contains a novel zinc-ribbon motif

Poly(ADP-ribose) polymerase-1 (PARP-1) is a multimodular nuclear protein that participates in many fundamental cellular activities. Stimulated by binding to nicked DNA, PARP-1 catalyzes poly(ADP-ribosyl)ation of the acceptor proteins using NAD (+) as a substrate. In this work, NMR methods were used to determine the solution structure of human PARP-1 protein. Domain C was found to contain a zinc-binding motif of three antiparallel beta-strands with four conserved cysteines positioned to coordinate the metal ligand, in addition to a helical region. The zinc-binding motif is structurally reminiscent of the "zinc-ribbon" fold, but with a novel spacing between the conserved cysteines (CX2CX12CX 9C). Domain C alone does not appear to bind to DNA. Interestingly, domain C is essential for PARP-1 activity, since a mixture containing nicked DNA and the PARP-1 ABDEF domains has only basal enzymatic activity, while the addition of domain C to the mixture initiated NAD (+) hydrolysis and the formation of poly(ADP-ribose), as detected by an NMR-based assay and autoradiography. The structural model for domain C in solution provides an important framework for further studies aimed at improving our understanding of how the various domains within the complex PARP-1 enzyme play their respective roles in regulating the enzyme activity when cells are under conditions of genotoxic stress.

Apoptosis pathways in fungal growth, development and ageing

Apoptosis is one type of programmed cell death with great importance for development and homeostasis of multicellular organisms. Unexpectedly, during the past decade, evidence has been obtained for the existence of a basal apoptosis machinery in yeast, as unicellular fungus, and in some filamentous fungi, a group of microorganisms that are neither true unicellular nor true multicellular biological systems but something in between. Here, we review evidence for a role of apoptotic processes in fungal pathogenicity, competitiveness, propagation, ageing and lifespan control.

basA regulates cell wall organization and asexual/sexual sporulation ratio in Aspergillus nidulans

Sphingolipid C4 hydroxylase catalyzes the conversion of dihydrosphingosine to phytosphingosine. In Saccharomyces cerevisiae, Sur2 is essential for sphingolipid C4 hydroxylation activity but not essential for normal growth. Here we demonstrate that the Aspergillus nidulans Sur2 homolog BasA is also required for phytosphingosine biosynthesis but is also essential for viability. We previously reported that a point missense mutation in basA resulted in aberrant cell wall thickening. Here our data suggest that accumulation of dihydrosphingosine is responsible for this phenotype. In addition, two different mutations in basA consistently accelerated the transition from asexual development to sexual development compared to the wild-type strain. The phenotype could be suppressed by exogenous addition of phytosphingosine. Northern analysis suggests that faster sexual development in the basA mutant might be due to a higher transcription level of ppoA and steA, genes demonstrated to coordinate a balance between asexual and sexual development in A. nidulans. Consistent with these findings, mutations in the ceramide-synthase-encoding genes barA and lagA also caused faster transition from asexual to sexual development, supporting the involvement of sphingolipid metabolism in fungal morphogenesis.

Non-self recognition and programmed cell death in filamentous fungi

Non-self recognition resulting in programmed cell death is a ubiquitous phenomenon in filamentous ascomycete fungi and is termed heterokaryon incompatibility (HI). Recent analyses show that genes containing predicted HET domains are often involved in HI; however, the function of the HET domain is unknown. Autophagy is induced as a consequence of HI, whereas the presence of a predicted transcription factor, VIB-1, is required for HI. Morphological features associated with apoptosis in filamentous fungi are induced by various stresses and drugs, and also during HI. Future analyses will reveal whether common or different genetic mechanisms trigger death by non-self recognition and death by various environmental onslaughts.

Transcriptome analysis of Aspergillus nidulans exposed to camptothecin-induced DNA damage

We have used an Aspergillus nidulans macroarray carrying sequences of 2,787 genes from this fungus to monitor gene expression of both wild-type and uvsB(ATR) (the homologue of the ATR gene) deletion mutant strains in a time course exposure to camptothecin (CPT). The results revealed a total of 1,512 and 1,700 genes in the wild-type and uvsB(ATR) deletion mutant strains that displayed a statistically significant difference at at least one experimental time point. We characterized six genes that have increased mRNA expression in the presence of CPT in the wild-type strain relative to the uvsB(ATR) mutant strain: fhdA (encoding a forkhead-associated domain protein), tprA (encoding a hypothetical protein that contains a tetratrico peptide repeat), mshA (encoding a MutS homologue involved in mismatch repair), phbA (encoding a prohibitin homologue), uvsC(RAD51) (the homologue of the RAD51 gene), and cshA (encoding a homologue of the excision repair protein ERCC-6 [Cockayne's syndrome protein]). The induced transcript levels of these genes in the presence of CPT require uvsB(ATR). These genes were deleted, and surprisingly, only the DeltauvsC mutant strain was sensitive to CPT; however, the others displayed sensitivity to a range of DNA-damaging and oxidative stress agents. These results indicate that the selected genes when inactivated display very complex and heterogeneous sensitivity behavior during growth in the presence of agents that directly or indirectly cause DNA damage. Moreover, with the exception of UvsC, deletion of each of these genes partially suppressed the sensitivity of the DeltauvsB strain to menadione and paraquat. Our results provide the first insight into the overall complexity of the response to DNA damage in filamentous fungi and suggest that multiple pathways may act in parallel to mediate DNA repair.