Among developmental regulators, StuA but not BrlA is essential for penicillin V production in Penicillium chrysogenum

Effects of MrwetA on Sexual Reproduction and Secondary Metabolism of Monascus ruber M7 Based on Transcriptome Analysis

wetA, one of the conidiation center regulatory genes in many filamentous fungi, plays an important role in promoting asexual spores (conidia) maturation. Our recent research has found that knocking out or overexpressing MrwetA (a homolog of wetA) in Monascus ruber M7 does not affect the development of its asexual spores like other fungi, but both repress the development of its sexual spores (ascospores). However, the mechanism remains unclear. In this study, the function of MrwetA on sexual reproduction and secondary metabolism in M. ruber M7 was confirmed by a complementary experiment. Moreover, the regulatory roles of MrwetA in modulating the expression of genes involved in sexual reproduction, meiosis, and biosynthesis of Monascus pigment and citrinin were analyzed based on the transcriptional data. These results not only contribute to clarifying the regulation of the reproduction and secondary metabolism of Monascus spp., but also to enriching the regulation molecular mechanism of reproduction in filamentous fungi.

CRISPR/Cas9-Mediated Disruption of the pcz1 Gene and Its Impact on Growth, Development, and Penicillin Production in Penicillium rubens

Penicillium rubens is a filamentous fungus of great biotechnological importance due to its role as an industrial producer of the antibiotic penicillin. However, despite its significance, our understanding of the regulatory mechanisms governing biological processes in this fungus is still limited. In fungi, zinc finger proteins containing a Zn(II)2Cys6 domain are particularly interesting regulators. Although the P. rubens genome harbors many genes encoding proteins with this domain, only two of them have been investigated thus far. In this study, we employed CRISPR-Cas9 technology to disrupt the pcz1 gene, which encodes a Zn(II)2Cys6 protein in P. rubens. The disruption of pcz1 resulted in a decrease in the production of penicillin in P. rubens. This decrease in penicillin production was accompanied by the downregulation of the expression of pcbAB, pcbC and penDE genes, which form the biosynthetic gene cluster responsible for penicillin production. Moreover, the disruption of pcz1 also impacts on asexual development, leading to decreased growth and conidiation, as well as enhanced conidial germination. Collectively, our results indicate that pcz1 acts as a positive regulator of penicillin production, growth, and conidiation, while functioning as a negative regulator of conidial germination in P. rubens. To the best of our knowledge, this is the first report involving a gene encoding a Zn(II)2Cys6 protein in the regulation of penicillin biosynthesis in P. rubens.

CfCpmd1 Regulates Pathogenicity and Sexual Development of Plus and Minus Strains in Colletotrichum fructicola Causing Glomerella Leaf Spot on Apple in China

Colletotrichum fructicola is a devastating fungal pathogen of diverse plants. Sexually compatible plus and minus strains occur in the same ascus. However, the differentiation mechanism of plus and minus strains remains poorly understood. Here, we characterized a novel Cys2-His2-containing transcription factor CfCpmd1. The plus CfCpmd1 deletion mutant (Δ+CfCpmd1) resulted in slow hyphal growth and a fluffy cotton-like colony, and the minus deletion mutant (Δ-CfCpmd1) exhibited characters similar to the wild type (WT). Δ+CfCpmd1 led to defective perithecial formation, whereas Δ-CfCpmd1 produced more and smaller perithecia. The normal mating line was developed by pairing cultures of Δ-CfCpmd1 and plus WT, whereas a weak line was observed between Δ+CfCpmd1 and minus WT. Conidial production was completely abolished in both plus and minus mutants. When inoculated on non-wounded apple leaves with mycelial plugs, Δ-CfCpmd1 was nonpathogenic because of failure to develop conidia and appressoria, while Δ+CfCpmd1 could infect apple leaves by appressoria differentiated directly from hyphal tips, even though no conidia formed. Collectively, our results demonstrate that CfCpmd1 of C. fructicola is an important gene related to plus and minus strain differentiation, which also affects hyphal growth, sporulation, appressorium formation, and pathogenicity.

AoMedA has a complex regulatory relationship with AoBrlA, AoAbaA, and AoWetA in conidiation, trap formation, and secondary metabolism in the nematode-trapping fungus Arthrobotrys oligospora

The asexual sporulation of filamentous fungi is an important mechanism for their reproduction, survival, and pathogenicity. In Aspergillus and several filamentous fungi, BrlA, AbaA, and WetA are the key elements of a central regulatory pathway controlling conidiation, and MedA is a developmental modifier that regulates temporal expression of central regulatory genes; however, their roles are largely unknown in nematode-trapping (NT) fungi. Arthrobotrys oligospora is a representative NT fungus, which can capture nematodes by producing adhesive networks (traps). Here, we characterized the function of AoMedA and three central developmental regulators (AoBrlA, AoAbaA, and AoWetA) in A. oligospora by gene disruption, phenotypic comparison, and multi-omics analyses, as these regulators are required for conidiation and play divergent roles in mycelial development, trap formation, lipid droplet accumulation, vacuole assembly, and secondary metabolism. A combined analysis of phenotypic traits and transcriptome showed that AoMedA and AoWetA are involved in the regulation of peroxisome, endocytosis, and autophagy. Moreover, yeast one-hybrid analysis showed that AoBrlA can regulate AoMedA, AoAbaA, and AoWetA, whereas AoMedA and AoAbaA can regulate AoWetA. Our results highlight the important roles of AoMedA, AoBrlA, AoAbaA, and AoWetA in conidiation, mycelia development, trap formation, and pathogenicity of A. oligospora and provide a basis for elucidating the relationship between conidiation and trap formation of NT fungi. IMPORTANCE Conidiation is the most common reproductive mode for many filamentous fungi and plays an essential role in the pathogenicity of fungal pathogens. Nematode-trapping (NT) fungi are a special group of filamentous fungi owing to their innate abilities to capture and digest nematodes by producing traps (trapping devices). Sporulation plays an important role in the growth and reproduction of NT fungi, and conidia are the basic components of biocontrol reagents for controlling diseases caused by plant-parasitic nematodes. Arthrobotrys oligospora is a well-known NT fungus and is a routinely used model fungus for probing the interaction between fungi and nematodes. In this study, the functions of four key regulators (AoMedA, AoBrlA, AoAbaA, and AoWetA) involved in conidiation were characterized in A. oligospora. A complex interaction between AoMedA and three central regulators was noted; these regulators are required for conidiation and trap formation and play a pleiotropic role in multiple intracellular activities. Our study first revealed the role of AoMedA and three central regulators in conidiation, trap formation, and pathogenicity of A. oligospora, which contributed to elucidating the regulatory mechanism of conidiation in NT fungi and helped in developing effective reagents for biocontrol of nematodes.

Penicillium chrysogenum, a Vintage Model with a Cutting-Edge Profile in Biotechnology

The discovery of penicillin entailed a decisive breakthrough in medicine. No other medical advance has ever had the same impact in the clinical practise. The fungus Penicillium chrysogenum (reclassified as P. rubens) has been used for industrial production of penicillin ever since the forties of the past century; industrial biotechnology developed hand in hand with it, and currently P. chrysogenum is a thoroughly studied model for secondary metabolite production and regulation. In addition to its role as penicillin producer, recent synthetic biology advances have put P. chrysogenum on the path to become a cell factory for the production of metabolites with biotechnological interest. In this review, we tell the history of P. chrysogenum, from the discovery of penicillin and the first isolation of strains with high production capacity to the most recent research advances with the fungus. We will describe how classical strain improvement programs achieved the goal of increasing production and how the development of different molecular tools allowed further improvements. The discovery of the penicillin gene cluster, the origin of the penicillin genes, the regulation of penicillin production, and a compilation of other P. chrysogenum secondary metabolites will also be covered and updated in this work.

Beyond the Biosynthetic Gene Cluster Paradigm: Genome-Wide Coexpression Networks Connect Clustered and Unclustered Transcription Factors to Secondary Metabolic Pathways

Fungal secondary metabolites are widely used as therapeutics and are vital components of drug discovery programs. A major challenge hindering discovery of novel secondary metabolites is that the underlying pathways involved in their biosynthesis are transcriptionally silent under typical laboratory growth conditions, making it difficult to identify the transcriptional networks that they are embedded in. Furthermore, while the genes participating in secondary metabolic pathways are typically found in contiguous clusters on the genome, known as biosynthetic gene clusters (BGCs), this is not always the case, especially for global and pathway-specific regulators of pathways’ activities. To address these challenges, we used 283 genome-wide gene expression data sets of the ascomycete cell factory Aspergillus niger generated during growth under 155 different conditions to construct two gene coexpression networks based on Spearman’s correlation coefficients (SCCs) and on mutual rank-transformed Pearson’s correlation coefficients (MR-PCCs). By mining these networks, we predicted six transcription factors, named MjkA to MjkF, to regulate secondary metabolism in A. niger. Overexpression of each transcription factor using the Tet-On cassette modulated the production of multiple secondary metabolites. We found that the SCC and MR-PCC approaches complemented each other, enabling the delineation of putative global (SCC) and pathway-specific (MR-PCC) transcription factors. These results highlight the potential of coexpression network approaches to identify and activate fungal secondary metabolic pathways and their products. More broadly, we argue that drug discovery programs in fungi should move beyond the BGC paradigm and focus on understanding the global regulatory networks in which secondary metabolic pathways are embedded.

IMPORTANCE There is an urgent need for novel bioactive molecules in both agriculture and medicine. The genomes of fungi are thought to contain vast numbers of metabolic pathways involved in the biosynthesis of secondary metabolites with diverse bioactivities. Because these metabolites are biosynthesized only under specific conditions, the vast majority of the fungal pharmacopeia awaits discovery. To discover the genetic networks that regulate the activity of secondary metabolites, we examined the genome-wide profiles of gene activity of the cell factory Aspergillus niger across hundreds of conditions. By constructing global networks that link genes with similar activities across conditions, we identified six putative global and pathway-specific regulators of secondary metabolite biosynthesis. Our study shows that elucidating the behavior of the genetic networks of fungi under diverse conditions harbors enormous promise for understanding fungal secondary metabolism, which ultimately may lead to novel drug candidates.

Characterization of the asexual developmental genes brlA and wetA in Monascus ruber M7

Monascus spp. are widely used in the production of monacolin K and food- grade pigments in East Asia. In Aspergillus species, the three transcription factors BrlA → AbaA → WetA sequentially function as the central activators of asexual development (conidiation), leading to the formation of conidiophores. Unlike their close relative Aspergillus spp., Monascus spp. produce basipetospora-type asexual spores (conidia), and their genomes contain homologs of brlA and wetA but not abaA. In the present study, to investigate their roles in Monascus conidiation, MrbrlA and MrwetA were functionally characterized by gene knockout and overexpression in Monascus ruber M7. The results revealed that the deletion and overexpression of MrbrlA and/or MrwetA caused no apparent changes in the morphology, size, number, structure, or germination of conidia. However, deletion and overexpression of MrwetA severely repressed sexual development and affected the production of secondary metabolites. Taken together, these results suggest that the well-established central regulatory model of conidiation in Aspergillus is not applicable in their Monascus relatives. The results of the present study could enrich our understanding of the asexual development regulatory networks in filamentous fungi.

Regulation of Secondary Metabolism in the Penicillium Genus

Penicillium, one of the most common fungi occurring in a diverse range of habitats, has a worldwide distribution and a large economic impact on human health. Hundreds of the species belonging to this genus cause disastrous decay in food crops and are able to produce a varied range of secondary metabolites, from which we can distinguish harmful mycotoxins. Some Penicillium species are considered to be important producers of patulin and ochratoxin A, two well-known mycotoxins. The production of these mycotoxins and other secondary metabolites is controlled and regulated by different mechanisms. The aim of this review is to highlight the different levels of regulation of secondary metabolites in the Penicillium genus.

The brlA Gene Deletion Reveals That Patulin Biosynthesis Is Not Related to Conidiation in Penicillium expansum

Dissemination and survival of ascomycetes is through asexual spores. The brlA gene encodes a C2H2-type zinc-finger transcription factor, which is essential for asexual development. Penicillium expansum causes blue mold disease and is the main source of patulin, a mycotoxin that contaminates apple-based food. A P. expansum PeΔbrlA deficient strain was generated by homologous recombination. In vivo, suppression of brlA completely blocked the development of conidiophores that takes place after the formation of coremia/synnemata, a required step for the perforation of the apple epicarp. Metabolome analysis displayed that patulin production was enhanced by brlA suppression, explaining a higher in vivo aggressiveness compared to the wild type (WT) strain. No patulin was detected in the synnemata, suggesting that patulin biosynthesis stopped when the fungus exited the apple. In vitro transcriptome analysis of PeΔbrlA unveiled an up-regulated biosynthetic gene cluster (PEXP_073960-PEXP_074060) that shares high similarity with the chaetoglobosin gene cluster of Chaetomium globosum. Metabolome analysis of PeΔbrlA confirmed these observations by unveiling a greater diversity of chaetoglobosin derivatives. We observed that chaetoglobosins A and C were found only in the synnemata, located outside of the apple, whereas other chaetoglobosins were detected in apple flesh, suggesting a spatial-temporal organization of the chaetoglobosin biosynthesis pathway.

Elaborated regulation of griseofulvin biosynthesis in Penicillium griseofulvum and its role on conidiation and virulence

Penicilium griseofulvum, the causal agent of apple blue mold, is able to produce in vitro and on apple a broad spectrum of secondary metabolites (SM), including patulin, roquefortine C and griseofulvin. Among them, griseofulvin is known for its antifungal and antiproliferative activity, and has received interest in many sectors, from medicine to agriculture. The biosynthesis of SM is finely regulated by filamentous fungi and can involve global regulators and pathway specific regulators, which are usually encoded by genes present in the same gene cluster as the backbone gene and tailoring enzymes. In the griseofulvin gene cluster, two putative transcription factors were previously identified, encoded by genes gsfR1 and gsfR2, and their role has been investigated in the present work. Analysis of P. griseofulvum knockout mutants lacking either gene suggest that gsfR2 forms part of a different pathway and gsfR1 exhibits many spectra of action, acting as regulator of griseofulvin and patulin biosynthesis and influencing conidia production and virulence on apple. The analysis of gsfR1 promoter revealed that the regulation of griseofulvin biosynthesis is also controlled by global regulators in response to many environmental stimuli, such as carbon and nitrogen. The influence of carbon and nitrogen on griseofulvin production was further investigated and verified, revealing a complex network of response and confirming the central role of gsfR1 in many processes in P. griseofulvum.

AoStuA, an APSES transcription factor, regulates the conidiation, trap formation, stress resistance and pathogenicity of the nematode-trapping fungus Arthrobotrys oligospora

The APSES protein family comprises a conserved class of fungus-specific transcriptional regulators. Some members have been identified in partial ascomycetes. In this study, the APSES protein StuA (AoStuA) of the nematode-trapping fungus Arthrobotrys oligospora was characterized. Compared with the wild-type (WT) strain, three ΔAoStuA mutants grew relatively slowly, displayed a 96% reduction in sporulation capacity and a delay in conidial germination. The reduced sporulation capacity correlated with transcriptional repression of several sporulation-related genes. The mutants were also more sensitive to chemical stressors than the WT strain. Importantly, the mutants were unable to produce mycelial traps for nematode predation. Moreover, peroxisomes and Woronin bodies were abundant in the WT cells but hardly found in the cells of those mutants. The lack of such organelles correlated with transcriptional repression of some genes involved in the biogenesis of peroxisomes and Woronin bodies. The transcript levels of several genes involved in the cAMP/PKA signalling pathway were also significantly reduced in the mutants versus the WT strain, implicating a regulatory role of AoStuA in the transcription of genes involved in the cAMP/PKA signalling pathway that regulates an array of cellular processes and events. In particular, AoStuA is indispensable for A. oligospora trap formation and virulence.

Proteomics and Penicillium chrysogenum: Unveiling the secrets behind penicillin production

Discovery, industrial production and clinical applications of penicillin, together with scientific findings on penicillin biosynthesis and its complex regulation, are model milestones of the historical evolution of the most recognized 'magic bullet' against microbial infections available in the worldwide market. Thousands of tons of penicillin produced nowadays are the result of a huge number of technical, industrial and scientific tackled and solved challenges. This combination of, sometimes unsuspected, findings has given Proteomics the chance to support the understanding of the physiology of the high-producing fungal strains and the development of enhanced mutants by means of inverse engineering. Thus, this review, which is part of the special issue entitled "A Tribute to J. Proteomics on its 10th Anniversary", describes how Proteomics has contributed to characterize different aspects related to penicillin production in Penicillium chrosogenum. It covers from global proteome characterizations (intracellular, extracellular and microbodies) to proteome-wide comparative analyses between different penicillin-producing mutant strains and conditions, paying special attention to the methodologies used, as well as to the most important outcomes. As a result, a guide of Proteomics approaches applied to the characterization of penicillin production by P. chrysogenum is detailed in the birthday of the Fleming's most relevant finding. SIGNIFICANCE: Although the discovery of penicillin is celebrating the 90th birthday and its clinical application is worldwide recognized, in fact, semisynthetic penicillins are still one of the most prescribed antibiotics, only the arrival of the post-genomic era during the first decade of the 21st century, and more precisely the Proteomics approaches, have contributed to unveil the industrial secrets behind penicillin production. This review provides relevant information, based on proteomics studies, about the molecular mechanisms responsible for increased penicillin titres, and therefore, may represent a clear model of inverse engineering in microorganisms.

Antifungal Peptides of the AFP Family Revisited: Are These Cannibal Toxins?

The emergence and spread of pathogenic fungi resistant to currently used antifungal drugs represents a serious challenge for medicine and agriculture. The use of smart antimicrobials, so-called “dirty drugs” which affect multiple cellular targets, is one strategy to prevent resistance. Of special interest is the exploitation of the AFP family of antimicrobial peptides, which include its founding member AFP from Aspergillus giganteus. This latter is a highly potent inhibitor of chitin synthesis and affects plasma membrane integrity in many human and plant pathogenic fungi. A transcriptomic meta-analysis of the afp-encoding genes in A. giganteus and A. niger predicts a role for these proteins during asexual sporulation, autophagy, and nutrient recycling, suggesting that AFPs are molecules important for the survival of A. niger and A. giganteus under nutrient limitation. In this review, we discuss parallels which exist between AFPs and bacterial cannibal toxins and provide arguments that the primary function of AFPs could be to kill genetically identical siblings. We hope that this review inspires computational and experimental biologists studying alternative explanations for the nature and function of antimicrobial peptides beyond the general assumption that they are mere defense molecules to fight competitors.

The developmental regulator Pcz1 affects the production of secondary metabolites in the filamentous fungus Penicillium roqueforti

Penicillium roqueforti is used in the production of several kinds of ripened blue-veined cheeses. In addition, this fungus produces interesting secondary metabolites such as roquefortine C, andrastin A and mycophenolic acid. To date, there is scarce information concerning the regulation of the production of these secondary metabolites. Recently, the gene named pcz1 (Penicillium C6 zinc domain protein 1) was described in P. roqueforti, which encodes for a Zn(II)₂Cys₆ protein that controls growth and developmental processes in this fungus. However, its effect on secondary metabolism is currently unknown. In this work, we have analyzed how the overexpression and down-regulation of pcz1 affect the production of roquefortine C, andrastin A and mycophenolic acid in P. roqueforti. The three metabolites were drastically reduced in the pcz1 down-regulated strains. However, when pcz1 was overexpressed, only mycophenolic acid was overproduced while, on the contrary, levels of roquefortine C and andrastin A were diminished. Importantly, these results match the expression pattern of key genes involved in the biosynthesis of these metabolites. Taken together, our results suggest that Pcz1 plays a key role in regulating secondary metabolism in the fungus Penicillium roqueforti.

An LaeA- and BrlA-Dependent Cellular Network Governs Tissue-Specific Secondary Metabolism in the Human Pathogen Aspergillus fumigatus

Biosynthesis of many ecologically important secondary metabolites (SMs) in filamentous fungi is controlled by several global transcriptional regulators, like the chromatin modifier LaeA, and tied to both development and vegetative growth. In Aspergillus molds, asexual development is regulated by the BrlA > AbaA > WetA transcriptional cascade. To elucidate BrlA pathway involvement in SM regulation, we examined the transcriptional and metabolic profiles of ΔbrlA, ΔabaA, and ΔwetA mutant and wild-type strains of the human pathogen Aspergillus fumigatus. We find that BrlA, in addition to regulating production of developmental SMs, regulates vegetative SMs and the SrbA-regulated hypoxia stress response in a concordant fashion to LaeA. We further show that the transcriptional and metabolic equivalence of the ΔbrlA and ΔlaeA mutations is mediated by an LaeA requirement preventing heterochromatic marks in the brlA promoter. These results provide a framework for the cellular network regulating not only fungal SMs but diverse cellular processes linked to virulence of this pathogen. IMPORTANCE Filamentous fungi produce a spectacular variety of small molecules, commonly known as secondary or specialized metabolites (SMs), which are critical to their ecologies and lifestyles (e.g., penicillin, cyclosporine, and aflatoxin). Elucidation of the regulatory network that governs SM production is a major question of both fundamental and applied research relevance. To shed light on the relationship between regulation of development and regulation of secondary metabolism in filamentous fungi, we performed global transcriptomic and metabolomic analyses on mutant and wild-type strains of the human pathogen Aspergillus fumigatus under conditions previously shown to induce the production of both vegetative growth-specific and asexual development-specific SMs. We find that the gene brlA, previously known as a master regulator of asexual development, is also a master regulator of secondary metabolism and other cellular processes. We further show that brlA regulation of SM is mediated by laeA, one of the master regulators of SM, providing a framework for the cellular network regulating not only fungal SMs but diverse cellular processes linked to virulence of this pathogen.

Dicer and Argonaute Genes Involved in RNA Interference in the Entomopathogenic Fungus Metarhizium robertsii

RNA interference (RNAi) is a gene-silencing mechanism that plays an important role in gene regulation in a number of eukaryotic organisms. Two core components, Dicer and Argonaute, are central in the RNAi machinery. However, the physiological roles of Dicer and Argonaute in the entomopathogenic fungus Metarhizium robertsii have remained unclear. Here, the roles of genes encoding Dicer (M. robertsiidcl1 [Mrdcl1] and Mrdcl2) and Argonaute (Mrago1 and Mrago2) proteins in M. robertsii were investigated. The results showed that the Dicer-like protein MrDCL2 and Argonaute protein MrAGO1 are the major components of the RNAi process occurring in M. robertsii The Dicer and Argonaute genes were not involved in the regulation of growth and diverse abiotic stress response in M. robertsii under the tested conditions. Moreover, our results showed that the Dicer and Argonaute gene mutants demonstrated reduced abilities to produce conidia, compared to the wild type (WT) and the gene-rescued mutant. In particular, the conidial yields in the Δdcl2 and Δago1 mutants were reduced by 55.8% and 59.3%, respectively, compared with those from the control strains. Subsequently, for the WT and Δdcl2 mutant strains, digital gene expression (DGE) profiling analysis of the stage of mycelium growth and conidiogenesis revealed that modest changes occur in development or metabolism processes, which may explain the reduction in conidiation in the Δdcl2 mutant. In addition, we further applied high-throughput sequencing technology to identify small RNAs (sRNAs) that are differentially expressed in the WT and the Δdcl2 mutant and found that 4 known microRNA-like small RNAs (milRNAs) and 8 novel milRNAs were Mrdcl2 dependent in M. robertsiiIMPORTANCE The identification and characterization of components in RNAi have contributed significantly to our understanding of the mechanism and functions of RNAi in eukaryotes. Here, we found that Dicer and Argonaute genes play an important role in regulating conidiation in M. robertsii Our study also demonstrates that diverse small RNA pathways exist in M. robertsii The study provides a theoretical platform for exploration of the functions of Dicer and Argonaute genes involved in RNAi in fungi.

A Transcriptome Meta-Analysis Proposes Novel Biological Roles for the Antifungal Protein AnAFP in Aspergillus niger

Understanding the genetic, molecular and evolutionary basis of cysteine-stabilized antifungal proteins (AFPs) from fungi is important for understanding whether their function is mainly defensive or associated with fungal growth and development. In the current study, a transcriptome meta-analysis of the Aspergillus niger γ-core protein AnAFP was performed to explore co-expressed genes and pathways, based on independent expression profiling microarrays covering 155 distinct cultivation conditions. This analysis uncovered that anafp displays a highly coordinated temporal and spatial transcriptional profile which is concomitant with key nutritional and developmental processes. Its expression profile coincides with early starvation response and parallels with genes involved in nutrient mobilization and autophagy. Using fluorescence- and luciferase reporter strains we demonstrated that the anafp promoter is active in highly vacuolated compartments and foraging hyphal cells during carbon starvation with CreA and FlbA, but not BrlA, as most likely regulators of anafp. A co-expression network analysis supported by luciferase-based reporter assays uncovered that anafp expression is embedded in several cellular processes including allorecognition, osmotic and oxidative stress survival, development, secondary metabolism and autophagy, and predicted StuA and VelC as additional regulators. The transcriptomic resources available for A. niger provide unparalleled resources to investigate the function of proteins. Our work illustrates how transcriptomic meta-analyses can lead to hypotheses regarding protein function and predict a role for AnAFP during slow growth, allorecognition, asexual development and nutrient recycling of A. niger and propose that it interacts with the autophagic machinery to enable these processes.

Putative methyltransferase LaeA and transcription factor CreA are necessary for proper asexual development and controlling secondary metabolic gene cluster expression

The morphological development of fungi is a complex process and is often coupled with secondary metabolite production. In this study, we assessed the function of putative methyltransferase LaeA and transcription factor CreA in controlling asexual development and secondary metabolic gene cluster expression in Penicillium oxalicum. The deletion of laeA (ΔlaeA) impaired the conidiation in P. oxalicum, with a downregulated expression of brlA. Overexpression of P. oxalicum brlA in ΔlaeA could upregulate brlA and abaA remarkably, but could not rescue the conidiation defect; therefore, brlA and abaA expression were necessary but not sufficient for conidiation. Deletion of creA in ΔlaeA background (ΔlaeAΔcreA) blocked conidiation with a white fluffy phenotype. Nutrient-rich medium could not rescue developmental defects in ΔlaeAΔcreA mutant but could rescue defects in ΔlaeA. Expression of 10 genes, namely, albA/wA, abrB/yA, arpA, aygA, arpA-like, arpB, arpB-like, rodA, rodA-like, and rodB, for pigmentation and spore wall protein genes was silenced in ΔlaeAΔcreA, whereas only six of them were downregulated in ΔlaeA. Among the 28 secondary metabolism gene clusters in P. oxalicum, four secondary metabolism gene clusters were silenced in ΔlaeA and two were also silenced in ΔbrlA mutant. A total of 10 physically linked and coregulated genes were distributed over five chromosomes in ΔlaeA. Six of these genes were located in subtelomeric regions, thus demonstrating a positional bias for LaeA-regulated clusters toward subtelomeric regions. All of silenced clusters located in subtelomeric regions were derepressed in ΔlaeAΔcreA, hence showing that lack of CreA could remediate the repression of gene clusters in ΔlaeA background. Results show that both putative methyltransferase LaeA and transcription factor CreA are necessary for proper asexual development and controlling secondary metabolic gene cluster expression.

Genome-Wide Chromatin Immunoprecipitation Sequencing Analysis of the Penicillium chrysogenum Velvet Protein PcVelA Identifies Methyltransferase PcLlmA as a Novel Downstream Regulator of Fungal Development

Penicillium chrysogenum is the sole industrial producer of the β-lactam antibiotic penicillin, which is the most commonly used drug for treating bacterial infections. In P. chrysogenum and other filamentous fungi, secondary metabolism and morphogenesis are controlled by the highly conserved multisubunit velvet complex. Here we present the first chromatin immunoprecipitation next-generation sequencing (ChIP-seq) analysis of a fungal velvet protein, providing experimental evidence that a velvet homologue in P. chrysogenum (PcVelA) acts as a direct transcriptional regulator at the DNA level in addition to functioning as a regulator at the protein level in P. chrysogenum, which was previously described. We identified many target genes that are related to processes known to be dependent on PcVelA, e.g., secondary metabolism as well as asexual and sexual development. We also identified seven PcVelA target genes that encode putative methyltransferases. Yeast two-hybrid and bimolecular fluorescence complementation analyses showed that one of the putative methyltransferases, PcLlmA, directly interacts with PcVelA. Furthermore, functional characterization of PcLlmA demonstrated that this protein is involved in the regulation of conidiosporogenesis, pellet formation, and hyphal morphology, all traits with major biotechnological relevance. IMPORTANCE Filamentous fungi are of major interest for biotechnological and pharmaceutical applications. This is due mainly to their ability to produce a wide variety of secondary metabolites, many of which are relevant as antibiotics. One of the most prominent examples is penicillin, a β-lactam antibiotic that is produced on the industrial scale by fermentation of P. chrysogenum. In recent years, the multisubunit protein complex velvet has been identified as one of the key regulators of fungal secondary metabolism and development. However, until recently, only a little has been known about how velvet mediates regulation at the molecular level. To address this issue, we performed ChIP-seq (chromatin immunoprecipitation in combination with next-generation sequencing) on and follow-up analysis of PcVelA, the core component of the velvet complex in P. chrysogenum. We demonstrate direct involvement of velvet in transcriptional control and present the putative methyltransferase PcLlmA as a new downstream factor and interaction partner of PcVelA.

The transcriptional regulators SteA and StuA contribute to keratin degradation and sexual reproduction of the dermatophyte Arthroderma benhamiae

Most superficial fungal infections are caused by dermatophytes, a specialized group of filamentous fungi which exclusively infect keratinized host structures such as hair, skin and nails. Since little is known about the molecular basis of pathogenicity and sexual reproduction in dermatophytes, here we functionally addressed two central transcriptional regulators, SteA and StuA. In the zoophilic species Arthroderma benhamiae a strategy for targeted genetic manipulation was recently established, and moreover, the species is teleomorphic and thus allows performing assays based on mating. By comparative genome analysis homologs of the developmental regulators SteA and StuA were identified in A. benhamiae. Knock-out mutants of the corresponding genes as well as complemented strains were generated and phenotypically characterized. In contrast to A. benhamiae wild type and complemented strains, both mutants failed to produce sexual reproductive structures in mating experiments. Analysis of growth on keratin substrates indicated that loss of steA resulted in the inability of ΔsteA mutants to produce hair perforation organs, but did not affect mycelia formation during growth on hair and nails. By contrast, ΔstuA mutants displayed a severe growth defect on these substrates, but were still able to produce hair perforations. Hence, formation of hair perforation organs and fungal growth on hair per se are differentially regulated processes. Our findings on the major role of SteA and StuA during sexual development and keratin degradation in A. benhamiae provide insights into their role in dermatophytes and further enhance our knowledge of basic biology and pathogenicity of these fungi.

Untargeted Metabolic Profiling of Winery-Derived Biomass Waste Degradation by Penicillium chrysogenum

Winery-derived biomass waste was degraded by Penicillium chrysogenum under solid state fermentation over 8 days in a (2)H2O-supplemented medium. Multivariate statistical analysis of the gas chromatography-mass spectrometry (GC-MS) data resulted in the identification of 94 significant metabolites, within 28 different metabolic pathways. The majority of biomass sugars were utilized by day 4 to yield products such as sugars, fatty acids, isoprenoids, and amino acids. The fungus was observed to metabolize xylose to xylitol, an intermediate of ethanol production. However, enzyme inhibition and autolysis were observed from day 6, indicating 5 days as the optimal time for fermentation. P. chrysogenum displayed metabolism of pentoses (to alcohols) and degraded tannins and lignins, properties that are lacking in other biomass-degrading ascomycetes. Rapid fermentation (3-5 days) may not only increase the pentose metabolizing efficiency but also increase the yield of medicinally important metabolites, such as syringate.

Identification of growth stage molecular markers in Trichoderma sp. 'atroviride type B' and their potential application in monitoring fungal growth and development in soil

Several members of the genus Trichoderma are biocontrol agents of soil-borne fungal plant pathogens. The effectiveness of biocontrol agents depends heavily on how they perform in the complex field environment. Therefore, the ability to monitor and track Trichoderma within the environment is essential to understanding biocontrol efficacy. The objectives of this work were to: (a) identify key genes involved in Trichoderma sp. 'atroviride type B' morphogenesis; (b) develop a robust RNA isolation method from soil; and (c) develop molecular marker assays for characterizing morphogenesis whilst in the soil environment. Four cDNA libraries corresponding to conidia, germination, vegetative growth and conidiogenesis were created, and the genes identified by sequencing. Stage specificity of the different genes was confirmed by either Northern blot or quantitative reverse-transcriptase PCR (qRT-PCR) analysis using RNA from the four stages. con10, a conidial-specific gene, was observed in conidia, as well as one gene also involved in subsequent stages of germination (L-lactate/malate dehydrogenase encoding gene). The germination stage revealed high expression rates of genes involved in amino acid and protein biosynthesis, while in the vegetative-growth stage, genes involved in differentiation, including the mitogen-activated protein kinase kinase similar to Kpp7 from Ustilago maydis and the orthologue to stuA from Aspergillus nidulans, were preferentially expressed. Genes involved in cell-wall synthesis were expressed during conidiogenesis. We standardized total RNA isolation from Trichoderma sp. 'atroviride type B' growing in soil and then examined the expression profiles of selected genes using qRT-PCR. The results suggested that the relative expression patterns were cyclic and not accumulative.

AcstuA, which encodes an APSES transcription regulator, is involved in conidiation, cephalosporin biosynthesis and cell wall integrity of Acremonium chrysogenum

A transcriptional regulatory gene AcstuA was identified from Acremonium chrysogenum. AcstuA encodes a basic helix-loop-helix protein with similarity to StuA which regulates the core developmental processes of Aspergillus nidulans. Like disruption of stuA in A. nidulans, deficiency of AcstuA blocked the conidiation of A. chrysogenum through severely down-regulating the expression of AcbrlA and AcabaA which encode orthologs of the key fungal developmental regulators BrlA and AbaA. Disruption of AcstuA also drastically reduced cephalosporin production of A. chrysogenum. In agreement, the transcriptions of pcbAB, pbcC, cefD1, cefD2, cefEF and cefG were remarkably decreased in the AcstuA disruption mutant (ΔAcstuA). In addition to defects in conidiation and cephalosporin biosynthesis, ΔAcstuA produced abnormal swollen and fragmented hyphal cells during fermentation. The phenotypic alterations of hyphal cells caused by AcstuA deletion were restored by supplementation of NaCl in the medium, indicating that the deficiency of AcstuA has an influence on the cell wall integrity of A. chrysogenum. The transcriptions of two putative mannoprotein encoding genes Acmp2 and Acmp3 significantly reduced in ΔAcstuA, further indicating that cell wall integrity of the mutant is impaired. These results strongly suggested that AcstuA is involved in conidiation, cephalosporin production, hyphal fragmentation and cell wall integrity in A. chrysogenum.

Systems approaches to predict the functions of glycoside hydrolases during the life cycle of Aspergillus niger using developmental mutants ∆brlA and ∆flbA

BACKGROUND

The filamentous fungus Aspergillus niger encounters carbon starvation in nature as well as during industrial fermentations. In response, regulatory networks initiate and control autolysis and sporulation. Carbohydrate-active enzymes play an important role in these processes, for example by modifying cell walls during spore cell wall biogenesis or in cell wall degradation connected to autolysis.

RESULTS

In this study, we used developmental mutants (ΔflbA and ΔbrlA) which are characterized by an aconidial phenotype when grown on a plate, but also in bioreactor-controlled submerged cultivations during carbon starvation. By comparing the transcriptomes, proteomes, enzyme activities and the fungal cell wall compositions of a wild type A. niger strain and these developmental mutants during carbon starvation, a global overview of the function of carbohydrate-active enzymes is provided. Seven genes encoding carbohydrate-active enzymes, including cfcA, were expressed during starvation in all strains; they may encode enzymes involved in cell wall recycling. Genes expressed in the wild-type during starvation, but not in the developmental mutants are likely involved in conidiogenesis. Eighteen of such genes were identified, including characterized sporulation-specific chitinases and An15g02350, member of the recently identified carbohydrate-active enzyme family AA11. Eight of the eighteen genes were also expressed, independent of FlbA or BrlA, in vegetative mycelium, indicating that they also have a role during vegetative growth. The ΔflbA strain had a reduced specific growth rate, an increased chitin content of the cell wall and specific expression of genes that are induced in response to cell wall stress, indicating that integrity of the cell wall of strain ΔflbA is reduced.

CONCLUSION

The combination of the developmental mutants ΔflbA and ΔbrlA resulted in the identification of enzymes involved in cell wall recycling and sporulation-specific cell wall modification, which contributes to understanding cell wall remodeling mechanisms during development.

The APSES family proteins in fungi: Characterizations, evolution and functions

The APSES protein family belongs to transcriptional factors of the basic helix-loop-helix (bHLH) class, the originally described members (APSES: Asm1p, Phd1p, Sok2p, Efg1p and StuAp) are used to designate this group of proteins, and they have been identified as key regulators of fungal development and other biological processes. APSES proteins share a highly conserved DNA-binding domain (APSES domain) of about 100 amino acids, whose central domain is predicted to form a typical bHLH structure. Besides APSES domain, several APSES proteins also contain additional domains, such as KilA-N and ankyrin repeats. In recent years, an increasing number of APSES proteins have been identified from diverse fungi, and they involve in numerous biological processes, such as sporulation, cellular differentiation, mycelial growth, secondary metabolism and virulence. Most fungi, including Aspergillus fumigatus, Aspergillus nidulans, Candida albicans, Fusarium graminearum, and Neurospora crassa, contain five APSES proteins. However, Cryptococcus neoformans only contains two APSES proteins, and Saccharomyces cerevisiae contains six APSES proteins. The phylogenetic analysis showed the APSES domains from different fungi were grouped into four clades (A, B, C and D), which is consistent with the result of homologous alignment of APSES domains using DNAman. The roles of APSES proteins in clade C have been studied in detail, while little is known about the roles of other APSES proteins in clades A, B and D. In this review, the biochemical properties and functional domains of APSES proteins are predicted and compared, and the phylogenetic relationship among APSES proteins from various fungi are analyzed based on the APSES domains. Moreover, the functions of APSES proteins in different fungi are summarized and discussed.

Phylogeny, identification and nomenclature of the genus Aspergillus

Aspergillus comprises a diverse group of species based on morphological, physiological and phylogenetic characters, which significantly impact biotechnology, food production, indoor environments and human health. Aspergillus was traditionally associated with nine teleomorph genera, but phylogenetic data suggest that together with genera such as Polypaecilum, Phialosimplex, Dichotomomyces and Cristaspora, Aspergillus forms a monophyletic clade closely related to Penicillium. Changes in the International Code of Nomenclature for algae, fungi and plants resulted in the move to one name per species, meaning that a decision had to be made whether to keep Aspergillus as one big genus or to split it into several smaller genera. The International Commission of Penicillium and Aspergillus decided to keep Aspergillus instead of using smaller genera. In this paper, we present the arguments for this decision. We introduce new combinations for accepted species presently lacking an Aspergillus name and provide an updated accepted species list for the genus, now containing 339 species. To add to the scientific value of the list, we include information about living ex-type culture collection numbers and GenBank accession numbers for available representative ITS, calmodulin, β-tubulin and RPB2 sequences. In addition, we recommend a standard working technique for Aspergillus and propose calmodulin as a secondary identification marker.

A novel C2H2 transcription factor that regulates gliA expression interdependently with GliZ in Aspergillus fumigatus

Secondary metabolites are produced by numerous organisms and can either be beneficial, benign, or harmful to humans. Genes involved in the synthesis and transport of these secondary metabolites are frequently found in gene clusters, which are often coordinately regulated, being almost exclusively dependent on transcription factors that are located within the clusters themselves. Gliotoxin, which is produced by a variety of Aspergillus species, Trichoderma species, and Penicillium species, exhibits immunosuppressive properties and has therefore been the subject of research for many laboratories. There have been a few proteins shown to regulate the gliotoxin cluster, most notably GliZ, a Zn2Cys6 binuclear finger transcription factor that lies within the cluster, and LaeA, a putative methyltransferase that globally regulates secondary metabolism clusters within numerous fungal species. Using a high-copy inducer screen in A. fumigatus, our lab has identified a novel C2H2 transcription factor, which plays an important role in regulating the gliotoxin biosynthetic cluster. This transcription factor, named GipA, induces gliotoxin production when present in extra copies. Furthermore, loss of gipA reduces gliotoxin production significantly. Through protein binding microarray and mutagenesis, we have identified a DNA binding site recognized by GipA that is in extremely close proximity to a potential GliZ DNA binding site in the 5' untranslated region of gliA, which encodes an efflux pump within the gliotoxin cluster. Not surprisingly, GliZ and GipA appear to work in an interdependent fashion to positively control gliA expression.

An endogenous promoter for conditional gene expression in Acremonium chrysogenum: the xylan and xylose inducible promoter xyl1(P.)

Acremonium chrysogenum is the natural producer of the beta-lactam antibiotic cephalosporin C and therefore of significant biotechnological importance. Here we identified and characterized the xylanase-encoding xyl1 gene and demonstrate that its promoter, xyl1(P), is suitable for conditional expression of heterologous genes in A. chrysogenum. This was shown by xylose and xylan-inducible xyl1(P)-driven expression of genes encoding green fluorescence protein and phleomycin resistance. Moreover, we demonstrate the potential of the xyl1(P) promoter for selection marker recycling. Taken together, these finding will help to overcome the limitation in genetic tools in this important filamentous fungus.

WetA is required for conidiogenesis and conidium maturation in the ascomycete fungus Fusarium graminearum

Fusarium graminearum, a prominent fungal pathogen that infects major cereal crops, primarily utilizes asexual spores to spread disease. To understand the molecular mechanisms underlying conidiogenesis in F. graminearum, we functionally characterized the F. graminearum ortholog of Aspergillus nidulans wetA, which has been shown to be involved in conidiogenesis and conidium maturation. Deletion of F. graminearum wetA did not alter mycelial growth, sexual development, or virulence, but the wetA deletion mutants produced longer conidia with fewer septa, and the conidia were sensitive to acute stresses, such as oxidative stress and heat stress. Furthermore, the survival rate of aged conidia from the F. graminearum wetA deletion mutants was reduced. The wetA deletion resulted in vigorous generation of single-celled conidia through autophagy-dependent microcycle conidiation, indicating that WetA functions to maintain conidial dormancy by suppressing microcycle conidiation in F. graminearum. Transcriptome analyses demonstrated that most of the putative conidiation-related genes are expressed constitutively and that only a few genes are specifically involved in F. graminearum conidiogenesis. The conserved and distinct roles identified for WetA in F. graminearum provide new insights into the genetics of conidiation in filamentous fungi.

Penicillium decumbens BrlA extensively regulates secondary metabolism and functionally associates with the expression of cellulase genes

Penicillium decumbens has been used in the industrial production of lignocellulolytic enzymes in China for more than 15 years. Conidiation is essential for most industrial fungi because conidia are used as starters in the first step of fermentation. To investigate the mechanism of conidiation in P. decumbens, we generated mutants defective in two central regulators of conidiation, FluG and BrlA. Deletion of fluG resulted in neither "fluffy" phenotype nor alteration in conidiation, indicating possible different upstream mechanisms activating brlA between P. decumbens and Aspergillus nidulans. Deletion of brlA completely blocked conidiation. Further investigation of brlA expression in different media (nutrient-rich or nutrient-poor) and different culture states (liquid or solid) showed that brlA expression is required but not sufficient for conidiation. The brlA deletion strain exhibited altered hyphal morphology with more branches. Genome-wide expression profiling identified BrlA-dependent genes in P. decumbens, including genes previously reported to be involved in conidiation as well as previously reported chitin synthase genes and acid protease gene (pepB). The expression levels of seven secondary metabolism gene clusters (from a total of 28 clusters) were drastically regulated in the brlA deletion strain, including a downregulated cluster putatively involved in the biosynthesis of the mycotoxins roquefortine C and meleagrin. In addition, the expression levels of most cellulase genes were upregulated in the brlA deletion strain detected by real-time quantitative PCR. The brlA deletion strain also exhibited an 89.1 % increase in cellulase activity compared with the wild-type strain. The results showed that BrlA in P. decumbens not only has a key role in regulating conidiation, but it also regulates secondary metabolism extensively as well as the expression of cellulase genes.

Proteomics shows new faces for the old penicillin producer Penicillium chrysogenum

Fungi comprise a vast group of microorganisms including the Ascomycota (majority of all described fungi), the Basidiomycota (mushrooms or higher fungi), and the Zygomycota and Chytridiomycota (basal or lower fungi) that produce industrially interesting secondary metabolites, such as β-lactam antibiotics. These compounds are one of the most commonly prescribed drugs world-wide. Since Fleming's initial discovery of Penicillium notatum 80 years ago, the role of Penicillium as an antimicrobial source became patent. After the isolation of Penicillium chrysogenum NRRL 1951 six decades ago, classical mutagenesis and screening programs led to the development of industrial strains with increased productivity (at least three orders of magnitude). The new “omics” era has provided the key to understand the underlying mechanisms of the industrial strain improvement process. The review of different proteomics methods applied to P. chrysogenum has revealed that industrial modification of this microorganism was a consequence of a careful rebalancing of several metabolic pathways. In addition, the secretome analysis of P. chrysogenum has opened the door to new industrial applications for this versatile filamentous fungus.

The veA gene of the pine needle pathogen Dothistroma septosporum regulates sporulation and secondary metabolism

Fungi possess genetic systems to regulate the expression of genes involved in complex processes such as development and secondary metabolite biosynthesis. The product of the velvet gene veA, first identified and characterized in Aspergillus nidulans, is a key player in the regulation of both of these processes. Since its discovery and characterization in many Aspergillus species, VeA has been found to have similar functions in other fungi, including the Dothideomycete Mycosphaerella graminicola. Another Dothideomycete, Dothistroma septosporum, is a pine needle pathogen that produces dothistromin, a polyketide toxin very closely related to aflatoxin (AF) and sterigmatocystin (ST) synthesized by Aspergillus spp. Dothistromin is unusual in that, unlike most other secondary metabolites, it is produced mainly during the early exponential growth phase in culture. It was therefore of interest to determine whether the regulation of dothistromin production in D. septosporum differs from the regulation of AF/ST in Aspergillus spp. To begin to address this question, a veA ortholog was identified and its function analyzed in D. septosporum. Inactivation of the veA gene resulted in reduced dothistromin production and a corresponding decrease in expression of dothistromin biosynthetic genes. Expression of other putative secondary metabolite genes in D. septosporum such as polyketide synthases and non-ribosomal peptide synthases showed a range of different responses to loss of Ds-veA. Asexual sporulation was also significantly reduced in the mutants, accompanied by a reduction in the expression of a putative stuA regulatory gene. The mutants were, however, able to infect Pinus radiata seedlings and complete their life cycle under laboratory conditions. Overall this work suggests that D. septosporum has a veA ortholog that is involved in the control of both developmental and secondary metabolite biosynthetic pathways.

Impact of the Penicillium chrysogenum genome on industrial production of metabolites

The genome sequence of Penicillium chrysogenum has initiated a range of fundamental studies, deciphering the genetic secrets of the industrial penicillin producer. More than 60 years of classical strain improvement has resulted in major but delicate rebalancing of the intracellular metabolism leading to the impressive penicillin titres of the current production strains. Several leads for further improvement are being followed up, including the use of P. chrysogenum as a cell factory for other products than β-lactam antibiotics.

The small molecular mass antifungal protein of Penicillium chrysogenum--a mechanism of action oriented review

The β-lactam producing filamentous fungus Penicillium chrysogenum secretes a 6.25 kDa small molecular mass antifungal protein, PAF, which has a highly stable, compact 3D structure and is effective against a wide spectrum of plant and zoo pathogenic fungi. Its precise physiological functions and mode of action need to be elucidated before considering possible biomedical, agricultural or food technological applications. According to some more recent experimental data, PAF plays an important role in the fine-tuning of conidiogenesis in Penicillium chrysogenum. PAF triggers apoptotic cell death in sensitive fungi, and cell death signaling may be transmitted through two-component systems, heterotrimeric G protein coupled signal transduction and regulatory networks as well as via alteration of the Ca(2+) -homeostasis of the cells. Possible biotechnological applications of PAF are also outlined in the review.

Transcriptional regulatory elements in fungal secondary metabolism

Filamentous fungi produce a variety of secondary metabolites of diverse beneficial and detrimental activities to humankind. The genes required for a given secondary metabolite are typically arranged in a gene cluster. There is considerable evidence that secondary metabolite gene regulation is, in part, by transcriptional control through hierarchical levels of transcriptional regulatory elements involved in secondary metabolite cluster regulation. Identification of elements regulating secondary metabolism could potentially provide a means of increasing production of beneficial metabolites, decreasing production of detrimental metabolites, aid in the identification of 'silent' natural products and also contribute to a broader understanding of molecular mechanisms by which secondary metabolites are produced. This review summarizes regulation of secondary metabolism associated with transcriptional regulatory elements from a broad view as well as the tremendous advances in discovery of cryptic or novel secondary metabolites by genomic mining.

The paf gene product modulates asexual development in Penicillium chrysogenum

Penicillium chrysogenum secretes a low molecular weight, cationic and cysteine-rich protein (PAF). It has growth inhibitory activity against the model organism Aspergillus nidulans and numerous zoo- and phytopathogenic fungi but shows only minimal conditional antifungal activity against the producing organism itself. In this study we provide evidence for an additional function of PAF which is distinct from the antifungal activity against putative ecologically concurrent microorganisms. Our data indicate that PAF enhances conidiation in P. chrysogenum by modulating the expression of brlA, the central regulatory gene for mitospore development. A paf deletion strain showed a significant impairment of mitospore formation which sustains our hypothesis that PAF plays an important role in balancing asexual differentiation in P. chrysogenum.