Gβ-like CpcB plays a crucial role for growth and development of Aspergillus nidulans and Aspergillus fumigatus

The Gβ-like protein Bcgbl1 regulates development and pathogenicity of the gray mold Botrytis cinerea via modulating two MAP kinase signaling pathways

The fungal Gβ-like protein has been reported to be involved in a variety of biological processes, such as mycelial growth, differentiation, conidiation, stress responses and infection. However, molecular mechanisms of the Gβ-like protein in regulating fungal development and pathogenicity are largely unknown. Here, we show that the Gβ-like protein gene Bcgbl1 in the gray mold fungus Botrytis cinerea plays a pivotal role in development and pathogenicity by regulating the mitogen-activated protein (MAP) kinases signaling pathways. The Bcgbl1 deletion mutants were defective in mycelial growth, sclerotial formation, conidiation, macroconidial morphogenesis, plant adhesion, and formation of infection cushions and appressorium-like structures, resulting in a complete loss of pathogenicity. Bcgbl1 interacted with BcSte50, the adapter protein of the cascade of MAP kinase (MAPK). Bcgbl1 mutants had reduced phosphorylation levels of two MAPKs, namely Bmp1 and Bmp3, thereby reducing infection. However, deletion of Bcgbl1 did not affect the intracellular cAMP level, and exogenous cAMP could not restore the defects. Moreover, Bcgbl1 mutants exhibited defects in cell wall integrity and oxidative stress tolerance. Transcriptional profiling revealed that Bcgbl1 plays a global role in regulation of gene expression upon hydrophobic surface induction. We further uncovered that three target genes encoding the hydrophobic surface binding proteins (HsbAs) contributed to the adhesion and virulence of B. cinerea. Overall, these findings suggest that Bcgbl1 had multiple functions and provided new insights for deciphering the Bcgbl1-mediated network for regulating development and pathogenicity of B. cinerea.

Elucidating the Obligate Nature and Biological Capacity of an Invasive Fungal Corn Pathogen

Tar spot is a devasting corn disease caused by the obligate fungal pathogen Phyllachora maydis. Since its initial identification in the United States in 2015, P. maydis has become an increasing threat to corn production. Despite this, P. maydis has remained largely understudied at the molecular level, due to difficulties surrounding its obligate lifestyle. Here, we generated a significantly improved P. maydis nuclear and mitochondrial genome, using a combination of long- and short-read technologies, and also provide the first transcriptomic analysis of primary tar spot lesions. Our results show that P. maydis is deficient in inorganic nitrogen utilization, is likely heterothallic, and encodes for significantly more protein-coding genes, including secreted enzymes and effectors, than previous determined. Furthermore, our expression analysis suggests that, following primary tar spot lesion formation, P. maydis might reroute carbon flux away from DNA replication and cell division pathways and towards pathways previously implicated in having significant roles in pathogenicity, such as autophagy and secretion. Together, our results identified several highly expressed unique secreted factors that likely contribute to host recognition and subsequent infection, greatly increasing our knowledge of the biological capacity of P. maydis, which have much broader implications for mitigating tar spot of corn. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Regulators of the Asexual Life Cycle of Aspergillus nidulans

The genus Aspergillus, one of the most abundant airborne fungi, is classified into hundreds of species that affect humans, animals, and plants. Among these, Aspergillus nidulans, as a key model organism, has been extensively studied to understand the mechanisms governing growth and development, physiology, and gene regulation in fungi. A. nidulans primarily reproduces by forming millions of asexual spores known as conidia. The asexual life cycle of A. nidulans can be simply divided into growth and asexual development (conidiation). After a certain period of vegetative growth, some vegetative cells (hyphae) develop into specialized asexual structures called conidiophores. Each A. nidulans conidiophore is composed of a foot cell, stalk, vesicle, metulae, phialides, and 12,000 conidia. This vegetative-to-developmental transition requires the activity of various regulators including FLB proteins, BrlA, and AbaA. Asymmetric repetitive mitotic cell division of phialides results in the formation of immature conidia. Subsequent conidial maturation requires multiple regulators such as WetA, VosA, and VelB. Matured conidia maintain cellular integrity and long-term viability against various stresses and desiccation. Under appropriate conditions, the resting conidia germinate and form new colonies, and this process is governed by a myriad of regulators, such as CreA and SocA. To date, a plethora of regulators for each asexual developmental stage have been identified and investigated. This review summarizes our current understanding of the regulators of conidial formation, maturation, dormancy, and germination in A. nidulans.

Functional analysis of the bZIP-type transcription factors AtfA and AtfB in Aspergillus nidulans

Transcription factors (TFs) with the basic leucin zipper domain are key elements of the stress response pathways in filamentous fungi. In this study, we functionally characterized the two bZIP type TFs AtfA and AtfB by deletion (Δ) and overexpression (OE) of their encoding genes in all combination: ΔatfA, ΔatfB, ΔatfAΔatfB, ΔatfAatfBOE, ΔatfBatfAOE, atfAOE, atfBOE and atfAOEatfBOE in Aspergillus nidulans. Based on our previous studies, ΔatfA increased the sensitivity of the fungus to oxidative stress mediated by menadione sodium bisulfite (MSB) and tert-butylhydroperoxide (tBOOH), while ΔatfB was not sensitive to any oxidative stress generating agents, namely MSB, tBOOH and diamide at all. Contrarily, the ΔatfB mutant was sensitive to NaCl, but tolerant to sorbitol. Overexpression of atfB was able to compensate the MSB sensitivity of the ΔatfA mutant. Heavy metal stress elicited by CdCl2 reduced diameter of the atfBOE and atfAOEatfBOE mutant colonies to about 50% of control colony, while the cell wall stress generating agent CongoRed increased the tolerance of the ΔatfA mutant. When we tested the heat stress sensitivity of the asexual spores (conidiospores) of the mutants, we found that conidiospores of ΔatfAatfBOE and ΔatfBatfAOE showed nearly 100% tolerance to heat stress. Asexual development was negatively affected by ΔatfA, while atfAOE and atfAOE coupled with ΔatfB increased the number of conidiospores of the fungus approximately 150% compared to the control. Overexpression of atfB led to a 25% reduction in the number of conidiospores, but increased levels of abaA mRNA and size of conidiospores. Sexual fruiting body (cleistothecium) formation was diminished in the ΔatfA and the ΔatfAΔatfB mutants, while relatively elevated in the ΔatfB and the ΔatfBatfAOE mutants. Production of the mycotoxin sterigmatocystin (ST) was decreased to undetectable levels in the ΔatfA mutant, yet ST production was restored in the ΔatfAΔatfB mutant, suggesting that ΔatfB can suppress ST production defect caused by ΔatfA. Levels of ST were also significantly decreased in the ΔatfAatfBOE, ΔatfBatfAOE and atfAOEatfBOE mutants.

Tools for adapting to a complex habitat: G-protein coupled receptors in Trichoderma

Sensing the environment and interpretation of the received signals are crucial competences of living organisms in order to properly adapt to their habitat, succeed in competition and to reproduce. G-protein coupled receptors (GPCRs) are members of a large family of sensors for extracellular signals and represent the starting point of complex signaling cascades regulating a plethora of intracellular physiological processes and output pathways in fungi. In Trichoderma spp. current research involves a wide range of topics from enzyme production, light response and secondary metabolism to sexual and asexual development as well as biocontrol, all of which require delicate balancing of resources in response to the environmental challenges or biotechnological needs at hand, which are crucially impacted by the surroundings of the fungi and their intercellular signaling cascades triggering a precisely tailored response. In this review we summarize recent findings on sensing by GPCRs in Trichoderma, including the function of pheromone receptors, glucose sensing by CSG1 and CSG2, regulation of secondary metabolism by GPR8 and impacts on mycoparasitism by GPR1. Additionally, we provide an overview on structural determinants, posttranslational modifications and interactions for regulation, activation and signal termination of GPCRs in order to inspire future in depth analyses of their function and to understand previous regulatory outcomes of natural and biotechnological processes modulated or enabled by GPCRs.

Quantitative proteomic analysis of Neosartorya pseudofischeri ascospores subjected to heat treatment

Neosartorya pseudofischeri, a heat- resistant fungus, was isolated from contaminated blueberry juice in our laboratory. To obtain a better understanding of the cellular process of heat- resistant fungus, a quantitative proteomic investigation employing stable isotope labeling by peptide demethylation was conducted on changes in intracellular proteins of N. pseudofischeri ascospores subjected to heat treatment at 93 °C for 0, 1 or 8 min. In total, 811 proteins were identified and quantified. Using the normalized ratio of protein abundance, proteins that changed more than two- fold after heat treatment were identified as significantly increased or decreased proteins and grouped into four clusters based on their quantitative changes. Decreased proteins were found mainly involved in the central carbon metabolism, heat stress responses, reactive oxygen intermediates elimination and translation events. A group of proteins in relation to toxicant degradation and antibiotic neutralization linking to environmental adaptability and tolerance of heat- resistant, was also identified. These findings provide insights into protein changes of N. pseudofischeri ascospores and lay foundations for further investigations on heat- resistant molds using targeted quantitative approaches. SIGNIFICANCE OF THE RESEARCH: Heat- resistant fungi can survive pasteurization processes, and subsequently germinate and grow to cause spoilage of food products, leading to significant economic losses for the food industry and potential health risk for the consumers. To obtain a better understanding of the cellular process of heat- resistant fungi, a quantitative proteomic approach employing stable isotope labeling by peptide demethylation has been used to investigate the intracellular protein changes of N. pseudofischeri ascospores isolated from blueberry juice and subjected to heat treatment. 150 significantly changed proteins were grouped into four clusters based on their quantitative changes. The significant decrease in protein abundance in response to heat treatment revealed possible mechanism that N. pseudofischeri ascospores could survive the heat treatment. This is the first proteomic profile report for N. pseudofischeri. These findings provide insights into protein changes of N. pseudofischeri and lay foundations for further investigations on heat- resistant fungi using targeted quantitative approaches to evaluate the efficiency of thermal treatment for processed food products.

The Gβ-like Protein AfCpcB Affects Sexual Development, Response to Oxidative Stress and Phagocytosis by Alveolar Macrophages in Aspergillus fumigatus

G-protein signaling is important for signal transduction, allowing various stimuli that are external to a cell to affect its internal molecules. In Aspergillus fumigatus, the roles of Gβ-like protein CpcB on growth, asexual development, drug sensitivity, and virulence in a mouse model have been previously reported. To gain a deeper insight into Aspergillus fumigatus sexual development, the ΔAfcpcB strain was generated using the supermater AFB62 strain and crossed with AFIR928. This cross yields a decreased number of cleistothecia, including few ascospores. The sexual reproductive organ-specific transcriptional analysis using RNAs from the cleistothecia (sexual fruiting bodies) indicated that the CpcB is essential for the completion of sexual development by regulating the transcription of sexual genes, such as veA, steA, and vosA. The ΔAfcpcB strain revealed increased resistance to oxidative stress by regulating genes for catalase, peroxiredoxin, and ergosterol biosynthesis. The ΔAfcpcB strain showed decreased uptake by alveolar macrophages in vitro, decreased sensitivity to Congo red, decreased expression of cell wall genes, and increased expression of the hydrophobin genes. Taken together, these findings indicate that AfCpcB plays important roles in sexual development, phagocytosis by alveolar macrophages, biosynthesis of the cell wall, and oxidative stress response.

The LAMMER Kinase, LkhA, Affects Aspergillus fumigatus Pathogenicity by Modulating Reproduction and Biosynthesis of Cell Wall PAMPs

The LAMMER kinase in eukaryotes is a well-conserved dual-specificity kinase. Aspergillus species cause a wide spectrum of diseases called aspergillosis in humans, depending on the underlying immune status of the host, such as allergy, aspergilloma, and invasive aspergillosis. Aspergillus fumigatus is the most common opportunistic fungal pathogen that causes invasive aspergillosis. Although LAMMER kinase has various functions in morphology, development, and cell cycle regulation in yeast and filamentous fungi, its function in A. fumigatus is not known. We performed molecular studies on the function of the A. fumigatus LAMMER kinase, AfLkhA, and reported its involvement in multiple cellular processes, including development and virulence. Deletion of AflkhA resulted in defects in colonial growth, production of conidia, and sexual development. Transcription and genetic analyses indicated that AfLkhA modulates the expression of key developmental regulatory genes. The AflkhA-deletion strain showed increased production of gliotoxins and protease activity. When conidia were challenged with alveolar macrophages, enodocytosis of conidia by macrophages was increased in the AflkhA-deletion strain, resulting from changes in expression of the cell wall genes and thus content of cell wall pathogen-associated molecular patterns, including β-1,3-glucan and GM. While T cell-deficient zebrafish larvae were significantly susceptible to wild-type A. fumigatus infection, AflkhA-deletion conidia infection reduced host mortality. A. fumigatus AfLkhA is required for the establishment of virulence factors, including conidial production, mycotoxin synthesis, protease activity, and interaction with macrophages, which ultimately affect pathogenicity at the organismal level.

Role of AcndtA in cleistothecium formation, osmotic stress response, pigmentation and carbon metabolism of Aspergillus cristatus

As the dominant fungus during the fermentation of Fuzhuan brick tea, Aspergillus cristatus is easily induced to undergo a sexual cycle under low-salt stress. However, the underlying regulatory mechanism of sexual reproduction is unclear. Here, we report a P53-like transcription factor AcndtA, which encodes an NDT80 DNA binding protein and regulates fungal reproduction, pigmentation and the stress response. Both insertion and deletion mutants of AcndtA exhibited a complete blockade of cleistothecium formation, and overexpressing AcndtA strains (OE: AcndtA) exhibited significantly reduced cleistothecium production, indicating that AcndtA plays a vital role in sexual development. Osmotic stress tests showed that overexpression of AcndtA had a negative impact on growth and conidia production. Additionally, AcndtA insertion, deletion and overexpression mutants exhibited reduced pigment formation. All the above developmental defects were reversed by the re-introduction of the AcndtA gene in ΔAcndtA. Moreover, the growth of AcndtA mutants in carbon-limited medium was better than that of the WT and OE: AcndtA strains, indicating that AcndtA is involved in carbon metabolism. Transcriptional profiling data showed that AcndtA regulated the expression of several genes related to development, osmotic stress and carbon metabolism.

Mannitol-1-phosphate dehydrogenase, MpdA, is required for mannitol production in vegetative cells and involved in hyphal branching, heat resistance of conidia and sexual development in Aspergillus nidulans

Aspergillus nidulans produces cleistothecia as sexual reproductive organs in a process affected by genetic and external factors. To gain a deeper insight into A. nidulans sexual development, we performed comparative proteome analyses based on the wild type developmental periods. We identified sexual development-specific proteins with a more than twofold increase in production during hypoxia or the sexual period compared to the asexual period. Among the sexual development-specific proteins analyzed by gene-deletion experiments and functional assays, MpdA, a putative mannitol-1-phosphate 5-dehydrogenase, plays multiple roles in growth and differentiation of A. nidulans. The most distinct mpdA-deletion phenotype was ascosporogenesis failure. Genetic mpdA deletion resulted in small cleistothecia with no functional ascospores. Transcriptional analyses indicated that MpdA modulates the expression of key development- and meiosis-regulatory genes during sexual development. The mpdA deletion increased hyphal branching and decreased conidial heat resistance. Mannitol production in conidia showed no difference, whereas it was decreased in mycelia and sexual cultures. Addition of mannitol during vegetative growth recovered the defects in conidial heat resistance and ascospore genesis. Taken together, these results indicate that MpdA plays an important role in sexual development, hyphal branching, and conidial heat resistance in Aspergillus nidulans.

Heterotrimeric G-protein signalers and RGSs in Aspergillus fumigatus

The heterotrimeric G-protein (G-protein) signaling pathway is one of the most important signaling pathways that transmit external signals into the inside of the cell, triggering appropriate biological responses. The external signals are sensed by various G-protein-coupled receptors (GPCRs) and transmitted into G-proteins consisting of the α, β, and γ subunits. Regulators of G-protein signaling (RGSs) are the key controllers of G-protein signaling pathways. GPCRs, G-proteins, and RGSs are the primary upstream components of the G-protein signaling pathway, and they are highly conserved in most filamentous fungi, playing diverse roles in biological processes. Recent studies characterized the G-protein signaling components in the opportunistic pathogenic fungus Aspergillus fumigatus. In this review, we have summarized the characteristics and functions of GPCRs, G-proteins, and RGSs, and their regulatory roles in governing fungal growth, asexual development, germination, stress tolerance, and virulence in A. fumigatus.

Survival factor SvfA plays multiple roles in differentiation and is essential for completion of sexual development in Aspergillus nidulans

The first member of the velvet family of proteins, VeA, regulates sexual development and secondary metabolism in the filamentous fungus Aspergillus nidulans. In our study, through comparative proteome analysis using wild type and veA-deletion strains, new putative regulators of sexual development were identified and functionally analyzed. Among these, SvfA, containing a yeast survival factor 1 domain, plays multiple roles in the growth and differentiation of A. nidulans. Deletion of the svfA gene resulted in increased sensitivity to oxidative and cold stress as in yeast. The svfA-deletion strain showed an increase in bi-polar germination and a decrease in radial growth rate. The deletion strain formed structurally abnormal conidiophores and thus produced lower amounts of conidiospores during asexual development. The svfA-deletion strain produced few Hülle cells and small cleistothecia with no ascospores, indicating the requirement of svfA for the completion of sexual development. Transcription and genetic analyses indicated that SvfA modulates the expression of key development regulatory genes. Western blot analysis revealed two forms of SvfA. The larger form showed sexual-specific and VeA-dependent production. Also, the deletion of svfA caused decreased ST (sterigmatocystin) production. We propose that SvfA is a novel central regulator of growth, differentiation and secondary metabolism in A. nidulans.

A WD40 Protein Encoding Gene Fvcpc2 Positively Regulates Mushroom Development and Yield in Flammulina velutipes

Ascomycota and Basidiomycota are two closely related phyla and fungi in two phyla share some common morphological developmental process during fruiting body formation. In Neurospora crassa, the Gβ-like protein CPC-2 with a seven-WD40 repeat domain was previously reported. By transforming CPC-2 ortholog encoding genes, from 7 different fungal species across Ascomycota and Basidiomycota, into the cpc-2 deletion mutant of N. crassa, we demonstrate that all tested CPC-2 ortholog genes were able to complement the defects of the cpc-2 deletion mutant in sexual development, indicating that CPC-2 proteins from Ascomycota and Basidiomycota have the similar cellular function. Using Flammulina velutipes as a model system for mushroom species, the CPC-2 ortholog FvCPC2 was characterized. Fvcpc2 increased transcription during fruiting body development. Knockdown of Fvcpc2 by RNAi completely impaired fruiting body formation. In three Fvcpc2 knockdown mutants, transcriptional levels of genes encoding adenylate cyclase and protein kinase A catalytic subunit were significantly lower and colony growth became slower than wild type. The addition of cAMP or the PKA-activator 8-Bromo-cAMP into the medium restored the Fvcpc2 knockdown mutants to the wild-type colony growth phenotype, suggesting that the involvement of cAMP production in the regulatory mechanisms of FvCPC2. Knockdown of Fvcpc2 also weakened transcriptional responses to sexual development induction by some genes related to fruiting body development, including 4 jacalin-related lectin encoding genes, 4 hydrophobin encoding genes, and 3 functionally-unknown genes, suggesting the participation of these genes in the mechanisms by which FvCPC2 regulates fruiting body development. All three Fvcpc2 overexpression strains displayed increased mushroom yield and shortened cultivation time compared to wild type, suggesting that Fvcpc2 can be a promising reference gene for Winter Mushroom breeding. Since the orthologs of FvCPC2 were highly conserved and specifically expressed during fruiting body development in different edible mushrooms, genes encoding FvCPC2 orthologs in other mushroom species also have potential application in breeding.

Characterization of non-canonical G beta-like protein FvGbb2 and its relationship with heterotrimeric G proteins in Fusarium verticillioides

Fusarium verticillioides is a fungal pathogen that is responsible for maize ear rot and stalk rot diseases worldwide. The fungus also produces carcinogenic mycotoxins, fumonisins on infested maize. Unfortunately, we still lack clear understanding of how the pathogen responds to host and environmental stimuli to trigger fumonisin biosynthesis. The heterotrimeric G protein complex, consisting of canonical Gα, Gβ and Gγ subunits, is involved in transducing signals from external stimuli to regulate downstream signal transduction pathways. Previously, we demonstrated that Gβ protein FvGbb1 directly impacts fumonisin regulation but not other physiological aspects in F. verticillioides. In this study, we identified and characterized a RACK1 (Receptor for Activated C Kinase 1) homolog FvGbb2 as a putative Gβ-like protein in F. verticillioides. The mutant exhibited severe defects not only in fumonisin biosynthesis but also vegetative growth and conidiation. FvGbb2 was positively associated with carbon source utilization and stress agents but negatively regulated general amino acid control. While FvGbb2 does not interact with canonical G protein subunits, it may associate with diverse proteins in the cytoplasm to regulate vegetative growth, virulence, fumonisin biosynthesis and stress response in F. verticillioides.

Expression of sexual genes in Aspergillus fumigatus homogeneous culture produced by vegetative mass mating

There are presently no studies on the genes for sexual development of Aspergillus fumigatus in situ using mating culture, primarily because of challenging experimental conditions that require a significantly long period of induction and produce developmentally heterogenous culture, harboring very few sexual organs. In order to overcome these challenges, we developed an efficient and convenient procedure called 'vegetative mass mating (VeM)' for study at a molecular level. The VeM method enabled production of a developmentally homogenous A. fumigatus culture, harboring many sexual organs in a plate within a short period of two weeks. Feasibility of the use of VeM for functional study of genes during A. fumigatus sexual development was evaluated by analyzing the transcription pattern of genes involved in pheromone signal transduction and regulation of sexual development. Here, we present for the first time, an in situ expression pattern of sexual genes during the mating process, induced by the VeM method, which will enable and promote the sexual development study of A. fumigatus at the molecular level.

It's All in the Genes: The Regulatory Pathways of Sexual Reproduction in Filamentous Ascomycetes

Sexual reproduction in filamentous ascomycete fungi results in the production of highly specialized sexual tissues, which arise from relatively simple, vegetative mycelia. This conversion takes place after the recognition of and response to a variety of exogenous and endogenous cues, and relies on very strictly regulated gene, protein, and metabolite pathways. This makes studying sexual development in fungi an interesting tool in which to study gene-gene, gene-protein, and protein-metabolite interactions. This review provides an overview of some of the most important genes involved in this process; from those involved in the conversion of mycelia into sexually-competent tissue, to those involved in the development of the ascomata, the asci, and ultimately, the ascospores.

The Aspergillus flavus Histone Acetyltransferase AflGcnE Regulates Morphogenesis, Aflatoxin Biosynthesis, and Pathogenicity

Histone acetyltransferases (HATs) help regulate fungal development and the production of secondary metabolites. In this study, we determined that the HAT AflGcnE influenced morphogenesis and aflatoxin biosynthesis in Aspergillus flavus. We observed that AflGcnE localized to the nucleus and cytoplasm during the conidial production and germination stages, while it was located mainly in the nucleus during the hyphal development stage. Deletion of AflgcnE inhibited the growth of A. flavus and decreased the hydrophobicity of the cell surface. The ΔAflgcnE mutant exhibited a lack of asexual sporulation and was unable to generate sclerotia. Additionally, AflgcnE was required to maintain cell wall integrity and genotoxic stress responses. Importantly, the ΔAflgcnE mutant did not produce aflatoxins, which was consistent with a significant down-regulation of aflatoxin gene expression levels. Furthermore, our data revealed that AflgcnE is a pathogenicity factor required for colonizing maize seeds. In summary, we revealed that A. flavus AflGcnE is crucial for morphological development, aflatoxin biosynthesis, stress responses, and pathogenicity. Our findings help clarify the functional divergence of GcnE orthologs, and may provide a possible target for controlling A. flavus infections of agriculturally important crops.

Roles of Rack1 Proteins in Fungal Pathogenesis

Pathogenic fungi cause diseases on various organisms. Despite their differences in life cycles, fungal pathogens use well-conserved proteins and pathways to regulate developmental and infection processes. In this review, we focus on Rack1, a multifaceted scaffolding protein involved in various biological processes. Rack1 is well conserved in eukaryotes and plays important roles in fungi, though limited studies have been conducted. To accelerate the study of Rack1 proteins in fungi, we review the functions of Rack1 proteins in model and pathogenic fungi and summarize recent progress on how Rack1 proteins are involved in fungal pathogenesis.

Negative regulation and developmental competence in Aspergillus

Asexual development (conidiation) in the filamentous fungus Aspergillus nidulans is governed by orchestrated gene expression. The three key negative regulators of conidiation SfgA, VosA, and NsdD act at different control point in the developmental genetic cascade. Here, we have revealed that NsdD is a key repressor affecting the quantity of asexual spores in Aspergillus. Moreover, nullifying both nsdD and vosA results in abundant formation of the development specific structure conidiophores even at 12 h of liquid culture, and near constitutive activation of conidiation, indicating that acquisition of developmental competence involves the removal of negative regulation exerted by both NsdD and VosA. NsdD's role in repressing conidiation is conserved in other aspergilli, as deleting nsdD causes enhanced and precocious activation of conidiation in Aspergillus fumigatus or Aspergillus flavus. In vivo NsdD-DNA interaction analyses identify three NsdD binding regions in the promoter of the essential activator of conidiation brlA, indicating a direct repressive role of NsdD in conidiation. Importantly, loss of flbC or flbD encoding upstream activators of brlA in the absence of nsdD results in delayed activation of brlA, suggesting distinct positive roles of FlbC and FlbD in conidiation. A genetic model depicting regulation of conidiation in A. nidulans is presented.

Molecular Characterization of Gβ-Like Protein CpcB Involved in Antifungal Drug Susceptibility and Virulence in A. fumigatus

Aspergillus fumigatus is an airborne human fungal pathogen that can survive in a wide range of environmental condition. G protein complex transduces external signals from a variety of stimuli outside a cell to its interior effectors in all eukaryotes. Gβ-like CpcB (cross pathway control B) belongs to a WD40 repeat protein family with the conserved G-H and W-D residues. Previous studies have demonstrated that Gβ-like proteins cooperate with related signal transduction proteins to function during many important developmental processes in A. fumigatus. However, the molecular characteristics of Gβ-like CpcB have not yet been identified. In this study, we demonstrated that the G-H residues in WD repeat 1, 2, 3, and the W-D residue in WD repeat 2 of CpcB are required not only to control normal hyphal growth and conidiation but also to affect antifungal drug susceptibility. The enhanced drug resistance might be due to reduced intracellular drug accumulation and altered ergosterol component. Moreover, we find that the first G-H residue of CpcB plays an important role in the virulence of A. fumigatus. To our knowledge, this is the first report for finding the importance of the conserved G-H and W-D residues for a Gβ-like protein in understanding of G protein functions.

Genetic control of asexual development in aspergillus fumigatus

Aspergillus fumigatus is one of the most common fungi found in the environment. It is an opportunistic human pathogen causing invasive pulmonary aspergillosis with a high mortality rate in immunocompromised patients. Conidia, the asexual spores, serve as the main dispersal and infection agent allowing entrance of the fungus into the host through the respiratory tract. Therefore, understanding the asexual developmental process that gives rise to the conidia is of great interest to the scientific community and is currently the focus of an immense load of research being conducted. We have been studying the genetic basis that controls asexual development and gliotoxin biosynthesis in A. fumigatus. In this review, we discuss the genetic regulatory system that dictates conidiation in this important fungus by covering the roles of crucial genetic factors from the upstream heterotrimeric G-protein signaling components to the more specific downstream central activators of the conidiation pathway. In addition, other key asexual regulators including the velvet regulators, the Flb proteins and their associated regulatory factors are discussed.