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Morphological variation of filamentous fungi.a | Ustilago maydis infection of a corn cob (courtesy of Regine Kahmann and Jörg Kämper, Max-Planck Institute for Terrestrial Microbiology, Marburg). b | Scanning electron micrograph of a Magnoporthe grisea appressorium (arrow), a cell used by the fungus to infect its host (courtesy of Nick Talbot, University of Exeter) (diameter of the appressorium, 8.0 m). c | Fruiting body of Schizophyllum commune (courtesy of Luis Lugones and Han Wosten, University of Utrecht). The fruiting body is the structure that produces the sexual spores. d | Conidiophore of Aspergillus nidulans (courtesy of Michelle Momony, University of Georgia). The conidiophore is the specialized structure on which asexual spores develop.
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In the 1940s, screens for metabolic mutants of the filamentous fungus Neurospora crassa established the fundamental, one-to-one relationship between a gene and a specific protein, and also established fungi as important genetic organisms. Today, a wide range of filamentous species, which represents a billion years of evolutionary divergence, is use...
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... ascomycete fungi are phytopathogens and cause severe crop losses worldwide. Species such as Magnoporthe grisea produce a special infection structure known as an appressorium (shown in FIG. 1), and the development of this specialized cell is relevant to under- standing how fungi infect their hosts. The appressorium has a strong melanized wall and accumulates high con- centrations of glycerol that draw water into the cell. This allows very high internal pressures (measured at up to 8 MPa) 49 to build up. This pressure is ...
Citations
... Aspergillus nidulans is a model filamentous fungus widely used in fungal development and metabolism studies [1,2]. A. nidulans propagates through both asexual and sexual spores, but asexual spores are their primary reproductive particle [3,4]. Spores germinate to form germ tubes and a web-like mass of fungal hyphae [5]. ...
The forkhead domain genes are important for development and morphogenesis in fungi. Six forkhead genes fkhA-fkhF have been found in the genome of the model filamentous Ascomycete Aspergillus nidulans. To identify the fkh gene(s) associated with fungal development, we examined mRNA levels of these six genes and found that the level of fkhB and fkhD mRNA was significantly elevated during asexual development and in conidia. To investigate the roles of FkhB and FkhD, we generated fkhB and fkhD deletion mutants and complemented strains and investigated their phenotypes. The deletion of fkhB, but not fkhD, affected fungal growth and both sexual and asexual development. The fkhB deletion mutant exhibited decreased colony size with distinctly pigmented (reddish) asexual spores and a significantly lower number of conidia compared with these features in the wild type (WT), although the level of sterigmatocystin was unaffected by the absence of fkhB. Furthermore, the fkhB deletion mutant produced sexual fruiting bodies (cleistothecia) smaller than those of WT, implying that the fkhB gene is involved in both asexual and sexual development. In addition, fkhB deletion reduced fungal tolerance to heat stress and decreased trehalose accumulation in conidia. Overall, these results suggest that fkhB plays a key role in proper fungal growth, development, and conidial stress tolerance in A. nidulans.
... Due to their strong influence on humankind, researchers initiated an investigation on metabolic mutants of the filamentous fungus Neurospora crassa in 1941, which established the basis of genetics: the one gene, one protein hypothesis. Since then, fungi have served as model organisms for eukaryotic genetic studies advancing the knowledge of modern genetics [1]. Among multitudinous fungi, the genus Aspergillus is comprised of the most common and ubiquitous fungi, with more than 340 species being identified [2]. ...
... Aspergillus fungi may undergo three different life cycles: asexual, sexual, and parasexual cycles [1]. Approximately only one-third of the identified Aspergillus species are known to have sexual development under appropriate conditions, and they primarily reproduce through asexual sporulation (conidiation) [3]. ...
In filamentous fungal Aspergillus species, growth, development, and secondary metabolism are genetically programmed biological processes, which require precise coordination of diverse signaling elements, transcription factors (TFs), upstream and downstream regulators, and biosynthetic genes. For the last few decades, regulatory roles of these controllers in asexual/sexual development and primary/secondary metabolism of Aspergillus species have been extensively studied. Among a wide spectrum of regulators, a handful of global regulators govern upstream regulation of development and metabolism by directly and/or indirectly affecting the expression of various genes including TFs. In this review, with the model fungus Aspergillus nidulans as the central figure, we summarize the most well-studied main upstream regulators and their regulatory roles. Specifically, we present key functions of heterotrimeric G proteins and G protein-coupled receptors in signal transduction), the velvet family proteins governing development and metabolism, LaeA as a global regulator of secondary metabolism, and NsdD, a key GATA-type TF, affecting development and secondary metabolism and provide a snapshot of overall upstream regulatory processes underlying growth, development, and metabolism in Aspergillus fungi.
... Some Aspergillus species can be used for food fermentation, enzyme production, and research purposes 2 ; however, others act as opportunistic human pathogens or mycotoxin-producing fungi 3 . Aspergillus nidulans is an important model organism for filamentous fungi that is essential for genetic and fungal biology research but also produces a mycotoxin called sterigmatocystin 4 . Along with A. nidulans, several other Aspergillus species have been used to study biological processes in filamentous fungi 5 ...
Aspergillus spp. mainly reproduce asexually via asexual spores called conidia. In this study, we identified CsgA, a conidia-specific Zn2Cys6 transcription factor containing the GAL4-like zinc-finger domain, and characterized the roles of CsgA in the model organism Aspergillus nidulans. In A. nidulans, the ΔcsgA strain produced abnormal conidiophores and exhibited increased conidial production. The deletion of csgA resulted in impaired production of sexual fruiting bodies (cleistothecia) and lower mutA expression levels. Overexpression of csgA led to decreased conidia production but increased cleistothecia production, suggesting that CsgA is essential for proper asexual and sexual development in A. nidulans. In conidia, the deletion of csgA resulted in increased trehalose content, higher spore viability, and increased tolerance to thermal and oxidative stresses. Transcriptomic analysis revealed that the loss of csgA affects the expression of genes related to conidia germination, DNA repair, and secondary metabolite biosynthesis. Further analysis revealed that the ΔcsgA strain exhibited delayed conidial germination and abnormal germ tube length. Additionally, the production of sterigmatocystin increased in the ΔcsgA conidia compared to that in the controls. Overall, these results suggest that CsgA is crucial for proper fungal development, spore viability, conidial germination, and sterigmatocystin production in A. nidulans.
... The gene knock-in is performed by the insertion of a new gene in the targeted site of the organism. Early gene manipulation techniques involve causing random mutations in the genome by exposing cells to various chemical and physical mutagens, and virus-induced "insertional mutations" (Casselton and Zolan, 2002). The isolation and recovery of the mutated gene in these approaches are a tedious process. ...
Functional genomics enhances the understanding of fundamental fungal biology and aids in improving the production of valuable bioactive fungal compounds. Available gene manipulation approaches to study filamentous fungi are generally inefficient, time-consuming, and laborious. A robust genomic technology CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) is a simple, effective, and precise genome editing tool that has revolutionized gene editing and systematic research on filamentous fungi. This chapter provides an insight into the concepts and recent developments of CRISPR-Cas9 tools for the precise change of endogenous genes and for the complete knock-out of their expression, transcriptional regulation and multiplex genome editing. In addition, the current and potential applications of the CRISPR-Cas9 system for decoding and confirmation of the fungal pathogenesis, metabolite engineering, biocontrol, chromatin dynamics, multiple signaling cascades, and cell imaging are highlighted. The chapter also describes various challenges faced in the development and applications of the CRISPR-Cas9 system. Further, the dilemmas associated with the potential applications of these tools in filamentous fungi are explored.
... Aspergillus nidulans is a model filamentous fungus widely used in fungal development and metabolism studies [1,2]. A. nidulans propagates through both asexual and sexual spores, but asexual spores are their primary reproductive particle [3,4]. Spores germinate to form germ tubes and a web-like mass of fungal hyphae [5]. ...
RNA-binding proteins are involved in RNA metabolism and posttranscriptional regulation of various fundamental biological processes. The PUF family of RNA-binding proteins is highly conserved in eukaryotes, and its members regulate gene expression, mitochondrial biogenesis, and RNA processing. However, their biological functions in Aspergillus species remain mostly unknown in filamentous fungi. Here we have characterized the puf genes in the model organism Aspergillus nidulans. We generated deletion mutant strains for the five putative puf genes present in the A. nidulans genome and investigated their developmental phenotypes. Deletion of pufA or pufE affected fungal growth and asexual development. pufA mutants exhibited decreased production of asexual spores and reduced mRNA expression of genes regulating asexual development. The pufE deletion reduced colony growth, increased formation of asexual spores, and delayed production of sexual fruiting bodies. In addition, the absence of pufE reduced both sterigmatocystin production and the mRNA levels of genes in the sterigmatocystin cluster. Finally, pufE deletion mutants showed reduced trehalose production and lower resistance to thermal stress. Overall, these results demonstrate that PufA and PufE play roles in the development and sterigmatocystin metabolism in A. nidulans.
... A conidiophore is composed of varying cell types and the process of its production is precisely regulated by multiple positive and negative regulators 10 . Some of these developmental regulators are thought to be conserved in Aspergillus species, and they have been extensively studied in the model fungus A. nidulans 11,12 . ...
McrA is a key transcription factor that functions as a global repressor of fungal secondary metabolism in Aspergillus species. Here, we report that mcrA is one of the VosA-VelB target genes and McrA governs the cellular and metabolic development in Aspergillus nidulans. The deletion of mcrA resulted in a reduced number of conidia and decreased mRNA levels of brlA, the key asexual developmental activator. In addition, the absence of mcrA led to a loss of long-term viability of asexual spores (conidia), which is likely associated with the lack of conidial trehalose and increased β-(1,3)-glucan levels in conidia. In supporting its repressive role, the mcrA deletion mutant conidia contain more amounts of sterigmatocystin and an unknown metabolite than the wild type conidia. While overexpression of mcrA caused the fluffy-autolytic phenotype coupled with accelerated cell death, deletion of mcrA did not fully suppress the developmental defects caused by the lack of the regulator of G-protein signaling protein FlbA. On the contrary to the cellular development, sterigmatocystin production was restored in the ΔflbA ΔmcrA double mutant, and overexpression of mcrA completely blocked the production of sterigmatocystin. Overall, McrA plays a multiple role in governing growth, development, spore viability, and secondary metabolism in A. nidulans.
... Most of these studies involved bioinformatically identifying candidate genes, obtaining knockout mutants, and comparative phenotyping. Classical mutagenesis followed by complementation had earlier led to the discovery of several novel genes in many fungi (Mattern et al., 1992;Casselton and Zolan, 2002). In recent years, the advancements in whole genome sequencing tools have allowed for identification of mutations in classically induced mutants of fungi . ...
Trichoderma virens is a commercial biofungicide used in agriculture. We have earlier isolated a mutant of T. virens using gamma ray-induced mutagenesis. This mutant, designated as M7, is defective in morphogenesis, secondary metabolism, and mycoparasitism. The mutant does not produce conidia, and the colony is hydrophilic. M7 cannot utilize cellulose and chitin as a sole carbon source and is unable to parasitize the plant pathogens Rhizoctonia solani and Pythium aphanidermatum in confrontation assay. Several volatile (germacrenes, beta-caryophyllene, alloaromadendrene, gamma-muurolene) and non-volatile (viridin, viridiol, gliovirin, heptelidic acid) metabolites are not detected in M7. In transcriptome analysis, many genes related to secondary metabolism, carbohydrate metabolism, hydrophobicity, and transportation, among others, were found to be downregulated in the mutant. Using whole genome sequencing, we identified five deletions in the mutant genome, totaling about 250 kb (encompassing 71 predicted ORFs), which was confirmed by PCR. This study provides novel insight into genetics of morphogenesis, secondary metabolism, and mycoparasitism and eventually could lead to the identification of novel regulators of beneficial traits in plant beneficial fungi Trichoderma spp. We also suggest that this mutant can be developed as a microbial cell factory for the production of secondary metabolites and proteins.
... To use Aspergillus species for the benefit of humanity, we must understand its biology. A. nidulans is a model organism for studies in fungal developmental biology and gene regulation; therefore, it is one of the best characterized Aspergillus species [13,14]. The reproductive modes of A. nidulans can be divided into two types, sexual and asexual [15]. ...
Filamentous fungi reproduce asexually or sexually, and the processes of asexual and sexual development are tightly regulated by a variety of transcription factors. In this study, we characterized a Zn2Cys6 transcription factor in two Aspergillus species, A. nidulans (AN5859) and A. flavus (AFLA_046870). AN5859 encodes a Zn2Cys6 transcription factor, called ZcfA. In A. nidulans, ΔzcfA mutants exhibit decreased fungal growth, a reduction in cleistothecia production, and increased asexual reproduction. Overexpression of zcfA results in increased conidial production, suggesting that ZcfA is required for proper asexual and sexual development in A. nidulans. In conidia, deletion of zcfA causes decreased trehalose levels and decreased spore viability but increased thermal sensitivity. In A. flavus, the deletion of the zcfA homolog AFLA_046870 causes increased conidial production but decreased sclerotia production; these effects are similar to those of zcfA deletion in A. nidulans development. Overall, these results demonstrate that ZcfA is essential for maintaining a balance between asexual and sexual development and that some roles of ZcfA are conserved in Aspergillus spp.
... The processes of sexual and asexual structure formation are complicated and are tightly regulated by a variety of regulators [4,11]. These studies have primarily focused on the model fungus Aspergillus nidulans [12,13]. ...
... A. nidulans is the model organism for genetic studies on fungal biology [12,14]. A. nidulans is a homothallic fungus that can produce sexual fruiting bodies without mating partners [7,15]. ...
The velvet regulator VosA plays a pivotal role in asexual sporulation in the model filamentous fungus Aspergillus nidulans. In the present study, we characterize the roles of VosA in sexual spores (ascospores) in A. nidulans. During ascospore maturation, the deletion of vosA causes a rapid decrease in spore viability. The absence of vosA also results in a lack of trehalose biogenesis and decreased tolerance of ascospores to thermal and oxidative stresses. RNA-seq-based genome-wide expression analysis demonstrated that the loss of vosA leads to elevated expression of sterigmatocystin (ST) biosynthetic genes and a slight increase in ST production in ascospores. Moreover, the deletion of vosA causes upregulation of additional gene clusters associated with the biosynthesis of other secondary metabolites, including asperthecin, microperfuranone, and monodictyphenone. On the other hand, the lack of vosA results in the downregulation of various genes involved in primary metabolism. In addition, vosA deletion alters mRNA levels of genes associated with the cell wall integrity and trehalose biosynthesis. Overall, these results demonstrate that the velvet regulator VosA plays a key role in the maturation and the cellular and metabolic integrity of sexual spores in A. nidulans.
... But others exert detrimental effects by producing toxic secondary metabolites called mycotoxins [1,4]. Among these species, A. nidulans has been a useful model system for investigating gene functions, not only of individual genes but also for elucidating networks of gene interactions [5,6]. A. flavus is an opportunistic pathogenic fungus that produces many toxic secondary metabolites, such as aflatoxin [7] and cyclopiazonic acid [8]. ...
MonA is a subunit of a guanine nucleotide exchange factor that is important for vacuole passing and autophagy processes in eukaryotes. In this study, we characterized the function of MonA, an orthologue of Saccharomyces cerevisiae Mon1, in the model fungus Aspergillus nidulans and a toxigenic fungus A. flavus. In A. nidulans, the absence of AnimonA led to decreased fungal growth, reduced asexual reproduction, and defective cleistothecia production. In addition, AnimonA deletion mutants exhibited decreased spore viability, had reduced trehalose contents in conidia, and were sensitive to thermal stress. In A. flavus, deletion of AflmonA caused decreased fungal growth and defective production of asexual spores and sclerotia structures. Moreover, the absence of monA affected vacuole morphology in both species. Taken together, these results indicate that MonA plays conserved roles in controlling fungal growth, development and vacuole morphology in A. nidulans and A. flavus.
