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Dautt-Castro M, Rosendo-Vargas M, Casas-Flores S. The Small GTPases in Fungal Signaling Conservation and Function. Cells 2021; 10:cells10051039. [PMID: 33924947 PMCID: PMC8146680 DOI: 10.3390/cells10051039] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 04/22/2021] [Accepted: 04/23/2021] [Indexed: 12/28/2022] Open
Abstract
Monomeric GTPases, which belong to the Ras superfamily, are small proteins involved in many biological processes. They are fine-tuned regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Several families have been identified in organisms from different kingdoms. Overall, the most studied families are Ras, Rho, Rab, Ran, Arf, and Miro. Recently, a new family named Big Ras GTPases was reported. As a general rule, the proteins of all families have five characteristic motifs (G1–G5), and some specific features for each family have been described. Here, we present an exhaustive analysis of these small GTPase families in fungi, using 56 different genomes belonging to different phyla. For this purpose, we used distinct approaches such as phylogenetics and sequences analysis. The main functions described for monomeric GTPases in fungi include morphogenesis, secondary metabolism, vesicle trafficking, and virulence, which are discussed here. Their participation during fungus–plant interactions is reviewed as well.
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Abstract
Aspergilli produce conidia for reproduction or to survive hostile conditions, and they are highly effective in the distribution of conidia through the environment. In immunocompromised individuals, inhaled conidia can germinate inside the respiratory tract, which may result in invasive pulmonary aspergillosis. The management of invasive aspergillosis has become more complex, with new risk groups being identified and the emergence of antifungal resistance. Patient survival is threatened by these developments, stressing the need for alternative therapeutic strategies. As germination is crucial for infection, prevention of this process might be a feasible approach. A broader understanding of conidial germination is important to identify novel antigermination targets. In this review, we describe conidial resistance against various stresses, transition from dormant conidia to hyphal growth, the underlying molecular mechanisms involved in germination of the most common Aspergillus species, and promising antigermination targets. Germination of Aspergillus is characterized by three morphotypes: dormancy, isotropic growth, and polarized growth. Intra- and extracellular proteins play an important role in the protection against unfavorable environmental conditions. Isotropically expanding conidia remodel the cell wall, and biosynthetic machineries are needed for cellular growth. These biosynthetic machineries are also important during polarized growth, together with tip formation and the cell cycle machinery. Genes involved in isotropic and polarized growth could be effective antigermination targets. Transcriptomic and proteomic studies on specific Aspergillus morphotypes will improve our understanding of the germination process and allow discovery of novel antigermination targets and biomarkers for early diagnosis and therapy.
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Zhi QQ, He L, Li JY, Li J, Wang ZL, He GY, He ZM. The Kinetochore Protein Spc105, a Novel Interaction Partner of LaeA, Regulates Development and Secondary Metabolism in Aspergillus flavus. Front Microbiol 2019; 10:1881. [PMID: 31456789 PMCID: PMC6700525 DOI: 10.3389/fmicb.2019.01881] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 07/30/2019] [Indexed: 01/04/2023] Open
Abstract
Nuclear protein LaeA is known as the global regulator of secondary metabolism in Aspergillus. LaeA connects with VeA and VelB to form a heterotrimeric complex, which coordinates fungal development and secondary metabolism. Here, we describe a new interaction partner of LaeA, the kinetochore protein Spc105, from the aflatoxin-producing fungus Aspergillus flavus. We showed that in addition to involvement in nuclear division, Spc105 is required for normal conidiophore development and sclerotia production of A. flavus. Moreover, Spc105 positively regulates the production of secondary metabolites such as aflatoxin and kojic acid, and negatively regulates the production of cyclopiazonic acid. Transcriptome analysis of the Δspc105 strain revealed that 23 backbone genes were differentially expressed, corresponding to 19 of the predicted 56 secondary metabolite gene clusters, suggesting a broad regulatory role of Spc105 in secondary metabolism. Notably, the reduced expression of laeA in our transcriptome data led to the discovery of the correlation between Spc105 and LaeA, and double mutant analysis indicated a functional interdependence between Spc105 and LaeA. Further, in vitro and in vivo protein interaction assays revealed that Spc105 interacts directly with the S-adenosylmethionine (SAM)-binding domain of LaeA, and that the leucine zipper motif in Spc105 is required for this interaction. The Spc105-LaeA interaction identified in our study indicates a cooperative interplay of distinct regulators in A. flavus, providing new insights into fungal secondary metabolism regulation networks.
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Affiliation(s)
- Qing-Qing Zhi
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Lei He
- Cancer Hospital and Institute of Guangzhou Medical University, Guangzhou, China
| | - Jie-Ying Li
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Jing Li
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Zhen-Long Wang
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Guang-Yao He
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Zhu-Mei He
- The Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
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Fischer GJ, Bacon W, Yang J, Palmer JM, Dagenais T, Hammock BD, Keller NP. Lipoxygenase Activity Accelerates Programmed Spore Germination in Aspergillus fumigatus. Front Microbiol 2017; 8:831. [PMID: 28536571 PMCID: PMC5422543 DOI: 10.3389/fmicb.2017.00831] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 04/24/2017] [Indexed: 12/31/2022] Open
Abstract
The opportunistic human pathogen Aspergillus fumigatus initiates invasive growth through a programmed germination process that progresses from dormant spore to swollen spore (SS) to germling (GL) and ultimately invasive hyphal growth. We find a lipoxygenase with considerable homology to human Alox5 and Alox15, LoxB, that impacts the transitions of programmed spore germination. Overexpression of loxB (OE::loxB) increases germination with rapid advance to the GL stage. However, deletion of loxB (ΔloxB) or its signal peptide only delays progression to the SS stage in the presence of arachidonic acid (AA); no delay is observed in minimal media. This delay is remediated by the addition of the oxygenated AA oxylipin 5-hydroxyeicosatetraenoic acid (5-HETE) that is a product of human Alox5. We propose that A. fumigatus acquisition of LoxB (found in few fungi) enhances germination rates in polyunsaturated fatty acid-rich environments.
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Affiliation(s)
- Gregory J Fischer
- Department of Genetics, University of Wisconsin-Madison, MadisonWI, USA
| | - William Bacon
- Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, MadisonWI, USA
| | - Jun Yang
- Department of Entomology and Nematology and Comprehensive Cancer Center, University of California, Davis, DavisCA, USA
| | - Jonathan M Palmer
- Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, MadisonWI, USA
| | - Taylor Dagenais
- Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, MadisonWI, USA
| | - Bruce D Hammock
- Department of Entomology and Nematology and Comprehensive Cancer Center, University of California, Davis, DavisCA, USA
| | - Nancy P Keller
- Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, MadisonWI, USA
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The low affinity glucose transporter HxtB is also involved in glucose signalling and metabolism in Aspergillus nidulans. Sci Rep 2017; 7:45073. [PMID: 28361917 PMCID: PMC5374493 DOI: 10.1038/srep45073] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 02/17/2017] [Indexed: 02/06/2023] Open
Abstract
One of the drawbacks during second-generation biofuel production from plant lignocellulosic biomass is the accumulation of glucose, the preferred carbon source of microorganisms, which causes the repression of hydrolytic enzyme secretion by industrially relevant filamentous fungi. Glucose sensing, subsequent transport and cellular signalling pathways have been barely elucidated in these organisms. This study therefore characterized the transcriptional response of the filamentous fungus Aspergillus nidulans to the presence of high and low glucose concentrations under continuous chemostat cultivation with the aim to identify novel factors involved in glucose sensing and signalling. Several transcription factor- and transporter-encoding genes were identified as being differentially regulated, including the previously characterized glucose and xylose transporter HxtB. HxtB was confirmed to be a low affinity glucose transporter, localizing to the plasma membrane under low- and high-glucose conditions. Furthermore, HxtB was shown to be involved in conidiation-related processes and may play a role in downstream glucose signalling. A gene predicted to encode the protein kinase PskA was also identified as being important for glucose metabolism. This study identified several proteins with predicted roles in glucose metabolic processes and provides a foundation for further investigation into the response of biotechnologically important filamentous fungi to glucose.
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Oda K, Terado S, Toyoura R, Fukuda H, Kawauchi M, Iwashita K. Development of a promoter shutoff system in Aspergillus oryzae using a sorbitol-sensitive promoter. Biosci Biotechnol Biochem 2016; 80:1792-801. [DOI: 10.1080/09168451.2016.1189313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Abstract
Promoter shutoff is a general method for analyzing essential genes, but in the fungus Aspergillus oryzae, no tightly repressed promoters have been reported. To overcome the current limitations of conditional promoters, we examined sorbitol- and galactose-responsive genes using microarrays to identify regulatable genes with only minor physiological and genetic effects. We identified two sorbitol-induced genes (designated as sorA and sorB), cloned their promoters, and built a regulated egfp and brlA expression system. Growth medium-dependent enhanced green fluorescence protein (EGFP) fluorescence and conidiation were confirmed for egfp and brlA under the control of their respective promoters. We also used this shutoff system to regulate the essential rhoA, which demonstrated the expected growth inhibition under repressed growth conditions. Our new sorbitol promoter shutoff system developed can serve as a valuable new tool for essential gene analyses of filamentous fungi.
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Affiliation(s)
- Ken Oda
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
| | - Shiho Terado
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
| | - Rieko Toyoura
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
| | - Hisashi Fukuda
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
| | - Moriyuki Kawauchi
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
| | - Kazuhiro Iwashita
- Division of Fundamental Research, National Research Institute of Brewing (NRIB), Hiroshima, Japan
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Cheng Y, Wang W, Yao J, Huang L, Voegele RT, Wang X, Kang Z. Two distinct Ras genes from Puccinia striiformis
exhibit differential roles in rust pathogenicity and cell death. Environ Microbiol 2016; 18:3910-3922. [DOI: 10.1111/1462-2920.13379] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 05/10/2016] [Indexed: 12/29/2022]
Affiliation(s)
- Yulin Cheng
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
| | - Wumei Wang
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
| | - Juanni Yao
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
| | - Lili Huang
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
| | - Ralf T. Voegele
- Fachgebiet Phytopathologie, Fakultät Agrarwissenschaften, Institut für Phytomedizin, Universität Hohenheim; Stuttgart Germany
| | - Xiaojie Wang
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
| | - Zhensheng Kang
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection; Northwest A&F University; Yangling Shaanxi 712100 People's Republic of China
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Aktipis CA, Boddy AM, Jansen G, Hibner U, Hochberg ME, Maley CC, Wilkinson GS. Cancer across the tree of life: cooperation and cheating in multicellularity. Philos Trans R Soc Lond B Biol Sci 2015; 370:20140219. [PMID: 26056363 PMCID: PMC4581024 DOI: 10.1098/rstb.2014.0219] [Citation(s) in RCA: 209] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/30/2015] [Indexed: 02/06/2023] Open
Abstract
Multicellularity is characterized by cooperation among cells for the development, maintenance and reproduction of the multicellular organism. Cancer can be viewed as cheating within this cooperative multicellular system. Complex multicellularity, and the cooperation underlying it, has evolved independently multiple times. We review the existing literature on cancer and cancer-like phenomena across life, not only focusing on complex multicellularity but also reviewing cancer-like phenomena across the tree of life more broadly. We find that cancer is characterized by a breakdown of the central features of cooperation that characterize multicellularity, including cheating in proliferation inhibition, cell death, division of labour, resource allocation and extracellular environment maintenance (which we term the five foundations of multicellularity). Cheating on division of labour, exhibited by a lack of differentiation and disorganized cell masses, has been observed in all forms of multicellularity. This suggests that deregulation of differentiation is a fundamental and universal aspect of carcinogenesis that may be underappreciated in cancer biology. Understanding cancer as a breakdown of multicellular cooperation provides novel insights into cancer hallmarks and suggests a set of assays and biomarkers that can be applied across species and characterize the fundamental requirements for generating a cancer.
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Affiliation(s)
- C Athena Aktipis
- Center for Evolution and Cancer, University of California San Francisco, San Francisco, CA 94143, USA Department of Psychology, Arizona State University, Tempe, AZ 85287-4501, USA Centre for Evolution and Cancer, Institute for Cancer Research, 123 Old Brompton Road, London SW7 3RP, UK Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Amy M Boddy
- Center for Evolution and Cancer, University of California San Francisco, San Francisco, CA 94143, USA Department of Psychology, Arizona State University, Tempe, AZ 85287-4501, USA Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Gunther Jansen
- Department of Evolutionary Ecology and Genetics, University of Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Urszula Hibner
- CNRS, UMR 5535, Institut de Génétique Moléculaire de Montpellier, Université de Montpellier, Montpellier, France Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Michael E Hochberg
- Institut des Sciences de l'Evolution, CNRS UMR5554, Université Montpellier, 34095 Montpellier, France Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Carlo C Maley
- Center for Evolution and Cancer, University of California San Francisco, San Francisco, CA 94143, USA Centre for Evolution and Cancer, Institute for Cancer Research, 123 Old Brompton Road, London SW7 3RP, UK Biodesign Institute, School of Life Sciences, Arizona State University, PO Box 8724501, Tempe, AZ 85287-4501, USA Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Gerald S Wilkinson
- Department of Biology, University of Maryland, College Park, MD 20742, USA Institute for Advanced Study, Wissenschaftskolleg zu Berlin, Berlin, Germany
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9
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Guan Y, Wang DY, Ying SH, Feng MG. A novel Ras GTPase (Ras3) regulates conidiation, multi-stress tolerance and virulence by acting upstream of Hog1 signaling pathway in Beauveria bassiana. Fungal Genet Biol 2015; 82:85-94. [PMID: 26162967 DOI: 10.1016/j.fgb.2015.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2015] [Revised: 07/01/2015] [Accepted: 07/06/2015] [Indexed: 12/18/2022]
Abstract
Two Ras ATPases (Ras1 and Ras2) are well known to regulate antagonistically or cooperatively various cellular events in many fungi. Here we show the significance of a novel Ras homolog (Ras3) for Beauveria bassiana. Ras3 possesses five domains and two GTP/GDP switches typical for Ras family and was proven to localize to plasma membrane despite the position change of a membrane-targeting cysteine in C-terminal CAAX motif. Deletion of ras3 altered temporal transcription pattern of ras1 instead of ras2. Compared with wild-type, Δras3 grew significantly faster in a rich medium but slower in some minimal media, and produced far fewer conidia with impaired quality, which was evident with slower germination, attenuated virulence, reduced thermotolerance and decreased UV-B resistance. Moreover, Δras3 was much more sensitive to the oxidative stress of menadione than of H2O2 and to the stress of high osmolarity than of cell wall perturbation during growth. The high sensitivity of Δras3 to menadione was concurrent with reductions in both gene transcripts and total activity of superoxide dismutases. Intriguingly, the high osmosensitivity was concurrent with not only reduced transcripts of a critical transcription factor (Msn2) and most signaling proteins in the high-osmolarity-glycerol pathway of Δras3 but nearly undetectable phosphorylation signal of Hog1 hallmarking the pathway. All the changes were restored by ras3 complementation. Taken together, Ras3 is involved in the Hog1 pathway required for osmoregulation and hence can positively regulate conidiation, germination, multi-stress tolerance and virulence linked to the biological control potential of the filamentous insect pathogen.
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Affiliation(s)
- Yi Guan
- Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Ding-Yi Wang
- Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Sheng-Hua Ying
- Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Ming-Guang Feng
- Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China.
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10
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Fortwendel JR. Orchestration of Morphogenesis in Filamentous Fungi: Conserved Roles for Ras Signaling Networks. FUNGAL BIOL REV 2015; 29:54-62. [PMID: 26257821 DOI: 10.1016/j.fbr.2015.04.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Filamentous fungi undergo complex developmental programs including conidial germination, polarized morphogenesis, and differentiation of sexual and asexual structures. For many fungi, the coordinated completion of development is required for pathogenicity, as specialized morphological structures must be produced by the invading fungus. Ras proteins are highly conserved GTPase signal transducers and function as major regulators of growth and development in eukaryotes. Filamentous fungi typically express two Ras homologues, comprising distinct groups of Ras1-like and Ras2-like proteins based on sequence homology. Recent evidence suggests shared roles for both Ras1 and Ras2 homologues, but also supports the existence of unique functions in the areas of stress response and virulence. This review focuses on the roles played by both Ras protein groups during growth, development, and pathogenicity of a diverse array of filamentous fungi.
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Affiliation(s)
- Jarrod R Fortwendel
- Department of Microbiology and Immunology, College of Medicine, University of South Alabama, Mobile, Alabama, USA
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11
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Arkowitz RA, Bassilana M. Regulation of hyphal morphogenesis by Ras and Rho small GTPases. FUNGAL BIOL REV 2015. [DOI: 10.1016/j.fbr.2015.02.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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12
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The observation of plcA mutation and localization in Aspergillus nidulans. J Microbiol 2014; 52:590-6. [PMID: 24972808 DOI: 10.1007/s12275-014-3651-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 04/09/2014] [Accepted: 04/18/2014] [Indexed: 10/25/2022]
Abstract
To know the function of the plcA gene, which encodes a putative phosphoinositide-specific phospholipase C, in a model filamentous fungus Aspergillus nidulans, it was disrupted thorough homologous recombination and examined. The germination rate of ΔplcA was reduced by approximately 65% and germination of ΔplcA at a lower temperature (25°C) was much slower than germination under normal conditions (37°C), suggesting the plcA is responsible for cold-sensitivity. The hyphal growth of ΔplcA was slightly reduced at 37°C and conspicuously reduced at 25°C. While germinating ΔplcA formed giant swollen spores, and generated short and thick hyphae. The results of the nuclear examination of ΔplcA showed nuclear division with missegregation, and the rate of nuclear division was lower than that of wild type at both 25°C and 37°C. The results of this study showed that plcA is localized to the nucleus through intracellular calcium signaling in A. nidulans. The abnormal nuclear division, resulting from plcA gene deletion, affects conidiation in asexual development. Taken together, these results suggested that plcA is required for normal vegetative growth, morphogenesis, conidiation, and nuclear division in A. nidulans.
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13
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Norton TS, Fortwendel JR. Control of Ras-mediated signaling in Aspergillus fumigatus. Mycopathologia 2014; 178:325-30. [PMID: 24952717 DOI: 10.1007/s11046-014-9765-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 05/28/2014] [Indexed: 12/13/2022]
Abstract
Pathogenic fungi employ numerous mechanisms to flourish in the stressful environment encountered within their mammalian hosts. Central to this arsenal for filamentous fungi is invasive growth within the host microenvironment, mediated by establishment and maintenance of polarized hyphal morphogenesis. In Aspergillus fumigatus, the RasA signal transduction pathway has emerged as a significant regulator of hyphal morphogenesis and virulence, among other processes. The factors contributing to the regulation of RasA itself are not as thoroughly understood, although proper temporal activation of RasA and spatial localization of RasA to the plasma membrane are known to play major roles. Interference with RasA palmitoylation or prenylation results in mislocalization of RasA and is associated with severe growth deficits. In addition, dysregulation of RasA activation results in severe morphologic aberrancies and growth deficits. This review highlights the relationship between RasA signaling, hyphal morphogenesis, and virulence in A. fumigatus and focuses on potential determinants of spatial and temporal RasA regulation.
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Affiliation(s)
- Tiffany S Norton
- Department of Microbiology and Immunology, College of Medicine, University of South Alabama, 5851 USA Drive North, MSB 2102, Mobile, AL, 36688, USA
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14
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Lu Y, Deng J, Rhodes JC, Lu H, Lu LJ. Predicting essential genes for identifying potential drug targets in Aspergillus fumigatus. Comput Biol Chem 2014; 50:29-40. [PMID: 24569026 DOI: 10.1016/j.compbiolchem.2014.01.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/23/2013] [Indexed: 12/31/2022]
Abstract
BACKGROUND Aspergillus fumigatus (Af) is a ubiquitous and opportunistic pathogen capable of causing acute, invasive pulmonary disease in susceptible hosts. Despite current therapeutic options, mortality associated with invasive Af infections remains unacceptably high, increasing 357% since 1980. Therefore, there is an urgent need for the development of novel therapeutic strategies, including more efficacious drugs acting on new targets. Thus, as noted in a recent review, "the identification of essential genes in fungi represents a crucial step in the development of new antifungal drugs". Expanding the target space by rapidly identifying new essential genes has thus been described as "the most important task of genomics-based target validation". RESULTS In previous research, we were the first to show that essential gene annotation can be reliably transferred between distantly related four Prokaryotic species. In this study, we extend our machine learning approach to the much more complex Eukaryotic fungal species. A compendium of essential genes is predicted in Af by transferring known essential gene annotations from another filamentous fungus Neurospora crassa. This approach predicts essential genes by integrating diverse types of intrinsic and context-dependent genomic features encoded in microbial genomes. The predicted essential datasets contained 1674 genes. We validated our results by comparing our predictions with known essential genes in Af, comparing our predictions with those predicted by homology mapping, and conducting conditional expressed alleles. We applied several layers of filters and selected a set of potential drug targets from the predicted essential genes. Finally, we have conducted wet lab knockout experiments to verify our predictions, which further validates the accuracy and wide applicability of the machine learning approach. CONCLUSIONS The approach presented here significantly extended our ability to predict essential genes beyond orthologs and made it possible to predict an inventory of essential genes in Eukaryotic fungal species, amongst which a preferred subset of suitable drug targets may be selected. By selecting the best new targets, we believe that resultant drugs would exhibit an unparalleled clinical impact against a naive pathogen population. Additional benefits that a compendium of essential genes can provide are important information on cell function and evolutionary biology. Furthermore, mapping essential genes to pathways may also reveal critical check points in the pathogen's metabolism. Finally, this approach is highly reproducible and portable, and can be easily applied to predict essential genes in many more pathogenic microbes, especially those unculturable.
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Affiliation(s)
- Yao Lu
- Shanghai Institute of Medical Genetics, Shanghai Children's Hospital, Shanghai Jiao Tong University, 24/1400 Beijing (W) Road, Shanghai 200040, PR China
| | - Jingyuan Deng
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC7024, Cincinnati, OH 45229, USA
| | - Judith C Rhodes
- Department of Pathology and Laboratory Medicine, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, OH 45221, USA
| | - Hui Lu
- Shanghai Institute of Medical Genetics, Shanghai Children's Hospital, Shanghai Jiao Tong University, 24/1400 Beijing (W) Road, Shanghai 200040, PR China; Department of Bioengineering (MC 063), University of Illinois at Chicago, 851 S Morgan St, 218 SEO, Chicago, IL 60607, USA.
| | - Long Jason Lu
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC7024, Cincinnati, OH 45229, USA; Division of Epidemiology and Biostatistics, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, MLC7024, Cincinnati, OH 45229, USA; Department of Computer Science, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, OH 45221, USA; Department of Environmental Health, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, OH 45221, USA; Department of Biomedical Engineering, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, OH 45221, USA.
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15
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Kalleda N, Naorem A, Manchikatla RV. Targeting fungal genes by diced siRNAs: a rapid tool to decipher gene function in Aspergillus nidulans. PLoS One 2013; 8:e75443. [PMID: 24130711 PMCID: PMC3794931 DOI: 10.1371/journal.pone.0075443] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 08/15/2013] [Indexed: 01/22/2023] Open
Abstract
Background Gene silencing triggered by chemically synthesized small interfering RNAs (siRNAs) has become a powerful tool for deciphering gene function in many eukaryotes. However, prediction and validation of a single siRNA duplex specific to a target gene is often ineffective. RNA interference (RNAi) with synthetic siRNA suffers from lower silencing efficacy, off-target effects and is cost-intensive, especially for functional genomic studies. With the explosion of fungal genomic information, there is an increasing need to analyze gene function in a rapid manner. Therefore, studies were performed in order to investigate the efficacy of gene silencing induced by RNase III-diced-siRNAs (d-siRNA) in model filamentous fungus, Aspergillus nidulans. Methodology/Principal Findings Stable expression of heterologous reporter gene in A. nidulans eases the examination of a new RNAi-induction route. Hence, we have optimized Agrobacterium tumefaciens-mediated transformation (AMT) of A. nidulans for stable expression of sGFP gene. This study demonstrates that the reporter GFP gene stably introduced into A. nidulans can be effectively silenced by treatment of GFP-d-siRNAs. We have shown the down-regulation of two endogenous genes, AnrasA and AnrasB of A. nidulans by d-siRNAs. We have also elucidated the function of an uncharacterized Ras homolog, rasB gene, which was found to be involved in hyphal growth and development. Further, silencing potency of d-siRNA was higher as compared to synthetic siRNA duplex, targeting AnrasA. Silencing was shown to be sequence-specific, since expression profiles of other closely related Ras family genes in d-siRNA treated AnrasA and AnrasB silenced lines exhibited no change in gene expression. Conclusions/Significance We have developed and applied a fast, specific and efficient gene silencing approach for elucidating gene function in A. nidulans using d-siRNAs. We have also optimized an efficient AMT in A. nidulans, which is useful for stable integration of transgenes.
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Affiliation(s)
| | - Aruna Naorem
- Department of Genetics, University of Delhi South Campus, New Delhi, India
| | - Rajam V. Manchikatla
- Department of Genetics, University of Delhi South Campus, New Delhi, India
- * E-mail:
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Noble LM, Andrianopoulos A. Reproductive competence: a recurrent logic module in eukaryotic development. Proc Biol Sci 2013; 280:20130819. [PMID: 23864594 PMCID: PMC3730585 DOI: 10.1098/rspb.2013.0819] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 06/14/2013] [Indexed: 02/06/2023] Open
Abstract
Developmental competence is the ability to differentiate in response to an appropriate stimulus, as first elaborated by Waddington in relation to organs and tissues. Competence thresholds operate at all levels of biological systems from the molecular (e.g. the cell cycle) to the ontological (e.g. metamorphosis and reproduction). Reproductive competence, an organismal process, is well studied in mammals (sexual maturity) and plants (vegetative phase change), though far less than later stages of terminal differentiation. The phenomenon has also been documented in multiple species of multicellular fungi, mostly in early, disparate literature, providing a clear example of physiological differentiation in the absence of morphological change. This review brings together data on reproductive competence in Ascomycete fungi, particularly the model filamentous fungus Aspergillus nidulans, contrasting mechanisms within Unikonts and plants. We posit reproductive competence is an elementary logic module necessary for coordinated development of multicellular organisms or functional units. This includes unitary multicellular life as well as colonial species both unicellular and multicellular (e.g. social insects such as ants). We discuss adaptive hypotheses for developmental and reproductive competence systems and suggest experimental work to address the evolutionary origins, generality and genetic basis of competence in the fungal kingdom.
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Affiliation(s)
- Luke M Noble
- Department of Genetics, University of Melbourne, Victoria 3010, Australia.
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van Leeuwen M, Krijgsheld P, Bleichrodt R, Menke H, Stam H, Stark J, Wösten H, Dijksterhuis J. Germination of conidia of Aspergillus niger is accompanied by major changes in RNA profiles. Stud Mycol 2013; 74:59-70. [PMID: 23449598 PMCID: PMC3563291 DOI: 10.3114/sim0009] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The transcriptome of conidia of Aspergillus niger was analysed during the first 8 h of germination. Dormant conidia started to grow isotropically two h after inoculation in liquid medium. Isotropic growth changed to polarised growth after 6 h, which coincided with one round of mitosis. Dormant conidia contained transcripts from 4 626 genes. The number of genes with transcripts decreased to 3 557 after 2 h of germination, after which an increase was observed with 4 780 expressed genes 8 h after inoculation. The RNA composition of dormant conidia was substantially different than all the subsequent stages of germination. The correlation coefficient between the RNA profiles of 0 h and 8 h was 0.46. They were between 0.76-0.93 when profiles of 2, 4 and 6 h were compared with that of 8 h. Dormant conidia were characterised by high levels of transcripts of genes involved in the formation of protecting components such as trehalose, mannitol, protective proteins (e.g. heat shock proteins and catalase). Transcripts belonging to the Functional Gene Categories (FunCat) protein synthesis, cell cycle and DNA processing and respiration were over-represented in the up-regulated genes at 2 h, whereas metabolism and cell cycle and DNA processing were over-represented in the up-regulated genes at 4 h. At 6 h and 8 h no functional gene classes were over- or under-represented in the differentially expressed genes. Taken together, it is concluded that the transcriptome of conidia changes dramatically during the first two h and that initiation of protein synthesis and respiration are important during early stages of germination.
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Affiliation(s)
- M.R. van Leeuwen
- Applied and Industrial Mycology, CBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands
| | - P. Krijgsheld
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentation, Molecular Microbiology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - R. Bleichrodt
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentation, Molecular Microbiology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - H. Menke
- DSM Food Specialties, PO Box 1, 2600 MA Delft, The Netherlands
| | - H. Stam
- DSM Food Specialties, PO Box 1, 2600 MA Delft, The Netherlands
| | - J. Stark
- DSM Food Specialties, PO Box 1, 2600 MA Delft, The Netherlands
| | - H.A.B. Wösten
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentation, Molecular Microbiology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - J. Dijksterhuis
- Applied and Industrial Mycology, CBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands
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Krijgsheld P, Bleichrodt R, van Veluw G, Wang F, Müller W, Dijksterhuis J, Wösten H. Development in Aspergillus. Stud Mycol 2013; 74:1-29. [PMID: 23450714 PMCID: PMC3563288 DOI: 10.3114/sim0006] [Citation(s) in RCA: 232] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The genus Aspergillus represents a diverse group of fungi that are among the most abundant fungi in the world. Germination of a spore can lead to a vegetative mycelium that colonizes a substrate. The hyphae within the mycelium are highly heterogeneous with respect to gene expression, growth, and secretion. Aspergilli can reproduce both asexually and sexually. To this end, conidiophores and ascocarps are produced that form conidia and ascospores, respectively. This review describes the molecular mechanisms underlying growth and development of Aspergillus.
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Affiliation(s)
- P. Krijgsheld
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - R. Bleichrodt
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - G.J. van Veluw
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - F. Wang
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - W.H. Müller
- Biomolecular Imaging, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - J. Dijksterhuis
- Applied and Industrial Mycology, CBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands
| | - H.A.B. Wösten
- Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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Xie XQ, Guan Y, Ying SH, Feng MG. Differentiated functions of Ras1 and Ras2 proteins in regulating the germination, growth, conidiation, multi-stress tolerance and virulence of Beauveria bassiana. Environ Microbiol 2012; 15:447-62. [PMID: 22958161 DOI: 10.1111/j.1462-2920.2012.02871.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2012] [Revised: 08/08/2012] [Accepted: 08/08/2012] [Indexed: 01/29/2023]
Abstract
Ras1 and Ras2 are two distinct Ras GTPases in Beauveria bassiana, an entomopathogenic fungus whose biocontrol potential against insect pests depends largely on virulence and multi-stress tolerance. The functions of both proteins were characterized for the first time by constructing dominant-active (GTP-bound) Ras1(G19V) and dominant-negative (GDP-bound) Ras1(D126A) and integrating them and normal Ras1 into wild type and ΔRas2 for a series of phenotypic and transcriptional analyses. The resultant mutants showed gradient changes of multiple phenotypes but little difference in conidial thermotolerance. Expression of Ras1(D126A) caused vigorous hyphal growth, severely defective conidiation, and increased tolerances to oxidation, cell wall disturbance, fungicide and UV-A/UV-B irradiations, but affected slightly germination, osmosensitivity and virulence. These phenotypes were antagonistically altered by mRas1(G19V) expressed in either wild type or ΔRas2, which was severely defective in conidial germination and hyphal growth and displayed intermediate changes in other mentioned phenotypes between paired mutants expressing Ras1(G19V) or Ras1(D126A) in wild type and ΔRas2. Their growth, UV tolerance or virulence was significantly correlated with cellular response to oxidation or cell wall disturbance. Transcriptional changes of 35 downstream effector genes involved in conidiation and multi-stress responses also related to most of the phenotypic changes among the mutants. Our findings highlight that Ras1 and Ras2 regulate differentially or antagonistically the germination, growth, conidiation, multi-stress tolerance and virulence of B. bassiana, thereby exerting profound effects on the fungal biocontrol potential.
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Affiliation(s)
- Xue-Qin Xie
- Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058 Zhejiang, China
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20
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Raudaskoski M, Kothe E, Fowler TJ, Jung EM, Horton JS. Ras and Rho small G proteins: insights from the Schizophyllum commune genome sequence and comparisons to other fungi. Biotechnol Genet Eng Rev 2012; 28:61-100. [PMID: 22616482 DOI: 10.5661/bger-28-61] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Unlike in animal cells and yeasts, the Ras and Rho small G proteins and their regulators have not received extensive research attention in the case of the filamentous fungi. In an effort to begin to rectify this deficiency, the genome sequence of the basidiomycete mushroom Schizophyllum commune was searched for all known components of the Ras and Rho signalling pathways. The results of this study should provide an impetus for further detailed investigations into their role in polarized hyphal growth, sexual reproduction and fruiting body development. These processes have long been the targets for genetic and cell biological research in this fungus.
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Affiliation(s)
- Marjatta Raudaskoski
- Department of Biology, University of Turku, Biocity A, Tykistökatu 6A, FI-20520 Turku, Finland
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21
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Zhang SR, Hao ZM, Wang LH, Shen S, Cao ZY, Xin YY, Hou ML, Gu SQ, Han JM, Dong JG. StRas2 regulates morphogenesis, conidiation and appressorium development in Setosphaeria turcica. Microbiol Res 2012; 167:478-86. [PMID: 22444434 DOI: 10.1016/j.micres.2012.02.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2012] [Revised: 02/22/2012] [Accepted: 02/26/2012] [Indexed: 11/18/2022]
Abstract
The proteins of Ras family are a large group of monomeric GTPases and act as molecular switches transducing extracellular signals into the cell in higher eukaryotes. However, little is known about roles of Ras family in the foliar pathogens. In this research, we cloned the gene named StRas2 encoding Ras in Setosphaeria turcica and investigated its function by RNA interference technology. We found that the growth rate of RNAi transformants named as R1, R2, R3, R4, R5 and R6, in which the StRas2 silencing efficiency fell in turn. With the highest silencing efficiency, the transformant R1 showed anomalistic hyphae morphology, indicating its growth was significantly affected. The transformants with a middle-silencing efficiency, such as R3, R4, displayed a delay when forming appressoria and invasive hyphae. R1 could not form conidia and appressoria. However, the conidial formation in R5 and R6 was significantly reduced, and these two transformants could form appressoria and penetrate the artificial cellophane, only that its invasive hyphae were fascicular and rarely branched. The HT-toxin biological activity of all transformants showed no difference. All results suggested that StRas2 is involved in the morphogenesis, conidiation, and appressorium development and is not related to the biosynthesis of HT-toxin.
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Affiliation(s)
- Shao-Ru Zhang
- Mycotoxins and Molecular Plant Pathology Laboratory, Agricultural University of Hebei, Baoding, China
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22
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23
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Zhu Y, Fang HM, Wang YM, Zeng GS, Zheng XD, Wang Y. Ras1 and Ras2 play antagonistic roles in regulating cellular cAMP level, stationary-phase entry and stress response in Candida albicans. Mol Microbiol 2009; 74:862-75. [PMID: 19788542 DOI: 10.1111/j.1365-2958.2009.06898.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The GTPase Ras1 activates the yeast-to-hypha transition in Candida albicans by activating cAMP synthesis. Here, we have characterized Ras2. Ras2 belongs to a group of atypical Ras proteins in some fungal species that share poor identity with other Ras GTPases with many variations in conserved motifs thought to be crucial for Ras-associated activities. We find that recombinant Ras2 is enzymatically as active as Ras1. However, only RAS1 can rescue the lethality of the Saccharomyces cerevisiae ras1 ras2 mutant, suggesting functional divergence of the two genes. ras2Delta is normal in hyphal growth, but deleting RAS2 in the ras1Delta background greatly aggravates the hyphal defect, indicating that Ras2 also has a role in hyphal development. Strikingly, while RAS1 deletion causes a approximately 20-fold decrease in cellular cAMP, further deletion of RAS2 restores it to approximately 30% of the wild-type level. Consistently, while the ras1Delta mutant enters the stationary phase prematurely, the double mutant does so normally. Moreover, ras1Delta cells exhibit increased resistance to H(2)O(2) and higher sensitivity to the heavy metal Co(2+), whereas ras2Delta cells show the opposite phenotypes. Together, our data reveal a novel regulatory mechanism by which two antagonizing Ras GTPases balance each other in regulating multiple cellular processes in C. albicans.
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Affiliation(s)
- Yong Zhu
- Institute of Molecular and Cell Biology, A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Singapore 138673, Singapore
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24
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Shi J, Chen W, Liu Q, Chen S, Hu H, Turner G, Lu L. Depletion of the MobB and CotA complex in Aspergillus nidulans causes defects in polarity maintenance that can be suppressed by the environment stress. Fungal Genet Biol 2008; 45:1570-81. [DOI: 10.1016/j.fgb.2008.08.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Revised: 08/18/2008] [Accepted: 08/19/2008] [Indexed: 11/30/2022]
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Georgianna DR, Payne GA. Genetic regulation of aflatoxin biosynthesis: from gene to genome. Fungal Genet Biol 2008; 46:113-25. [PMID: 19010433 DOI: 10.1016/j.fgb.2008.10.011] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Revised: 10/10/2008] [Accepted: 10/10/2008] [Indexed: 01/12/2023]
Abstract
Aflatoxins are notorious toxic secondary metabolites known for their impacts on human and animal health, and their effects on the marketability of key grain and nut crops. Understanding aflatoxin biosynthesis is the focus of a large and diverse research community. Concerted efforts by this community have led not only to a well-characterized biosynthetic pathway, but also to the discovery of novel regulatory mechanisms. Common to secondary metabolism is the clustering of biosynthetic genes and their regulation by pathway specific as well as global regulators. Recent data show that arrangement of secondary metabolite genes in clusters may allow for an important global regulation of secondary metabolism based on physical location along the chromosome. Available genomic and proteomic tools are now allowing us to examine aflatoxin biosynthesis more broadly and to put its regulation in context with fungal development and fungal ecology. This review covers our current understanding of the biosynthesis and regulation of aflatoxin and highlights new and emerging information garnered from structural and functional genomics. The focus of this review will be on studies in Aspergillus flavus and Aspergillus parasiticus, the two agronomically important species that produce aflatoxin. Also covered will be the important contributions gained by studies on production of the aflatoxin precursor sterigmatocystin in Aspergillus nidulans.
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Affiliation(s)
- D Ryan Georgianna
- Department of Plant Pathology, North Carolina State University, 851 Main Campus, Dr. Partners III Suite 267, Raleigh, NC 27606, Campus Box 7244, USA
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Osmani AH, Oakley BR, Osmani SA. Identification and analysis of essential Aspergillus nidulans genes using the heterokaryon rescue technique. Nat Protoc 2006; 1:2517-26. [PMID: 17406500 DOI: 10.1038/nprot.2006.406] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the heterokaryon rescue technique, gene deletions are carried out using the pyrG nutritional marker to replace the coding region of target genes via homologous recombination in Aspergillus nidulans. If an essential gene is deleted, the null allele is maintained in spontaneously generated heterokaryons that consist of two genetically distinct types of nuclei. One nuclear type has the essential gene deleted but has a functional pyrG allele (pyrG+). The other has the wild-type allele of the essential gene but lacks a functional pyrG allele (pyrG-). Thus, a simple growth test applied to the uninucleate asexual spores formed from primary transformants can identify deletions of genes that are non-essential from those that are essential and can only be propagated by heterokaryon rescue. The growth tests also enable the phenotype of the null allele to be defined. Diagnostic PCR can be used to confirm deletions at the molecular level. This technique is suitable for large-scale gene-deletion programs and can be completed within 3 weeks.
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Affiliation(s)
- Aysha H Osmani
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43210, USA
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Li G, Osborne J, Asiegbu FO. A macroarray expression analysis of novel cDNAs vital for growth initiation and primary metabolism during development of Heterobasidion parviporum conidiospores. Environ Microbiol 2006; 8:1340-50. [PMID: 16872398 DOI: 10.1111/j.1462-2920.2006.01027.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The pathogen Heterobasidion parviporum causes significant losses to forest industries in Europe and North America. The fungus is spread by basidiospores on fresh stumps where it differentiates into a specialized infection hyphae to colonize its host. This differentiation is driven by recognition and its strategic success lies in its ability to do this rapidly and efficiently. To investigate gene expression pattern during the spore germination stages, mRNA of germinated and ungerminated conidiospores of H. parviporum harvested at distinct developmental time points (18, 36, 72 and 120 h) corresponding to periods of isotropic/germ tube emergence, polarized apical, early and late mycelial lateral branching growth stages was hybridized to macroarrays containing 338 cDNAs from H. parviporum. The results of the statistical analysis identified a total of 24, 39, 38 and 30 genes that were differentially upregulated at 18, 36, 72 and 120 h, respectively, relative to time 0. The number of the downregulated genes was 4, 6, 8 and 13 genes respectively. During isotropic, polarized and mycelial growth stages, majority of the differentially expressed genes belonged to functional categories metabolism (21-32%) and protein formation (21-30%). Real-time polymerase chain reaction (real-time-PCR) data essentially confirmed the macroarray analyses. The real-time-PCR result showed that transcript levels of genes involved in glucose metabolism (phosphoglucomutase), amino acid metabolism (arginase, delta-1-pyrroline-5-carboxylate reductase, sulfur metabolism-negative regulator, imidazoleglycerol phosphate dehydratase) and protein synthesis (40S ribosomal protein S15) were significantly increased during polarized growth (36 h) stage but decreased at early and late stages of mycelial growth (72-120 h). An understanding of the various molecular and physiological processes during the development of H. parviporum spores is an important step towards the goal of identifying novel antifungal strategies.
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Affiliation(s)
- Guosheng Li
- Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Box 7026, 750 07, Uppsala, Sweden
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Brodhagen M, Keller NP. Signalling pathways connecting mycotoxin production and sporulation. MOLECULAR PLANT PATHOLOGY 2006; 7:285-301. [PMID: 20507448 DOI: 10.1111/j.1364-3703.2006.00338.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
SUMMARY Mycotoxin contamination of food and feed presents a serious food safety issue on a global scale, causing tremendous yield and economic losses. These toxins, produced largely by members of the genera Aspergillus and Fusarium, represent a subset of the impressive array of secondary metabolites produced by filamentous fungi. Some secondary metabolites are associated temporally and functionally with sporulation. In Aspergillus and Fusarium, sporulation and mycotoxin production are both regulated by G protein signalling pathways. G protein signalling pathways commonly regulate fungal development, stress response and expression of virulence traits. In addition, fungal development is influenced by external factors. Among these are lipids, and in particular, oxylipin signals, which may be derived from either the fungus or infected seeds. Regardless of origin, oxylipins have the potential to elicit profound changes in both sporulation and mycotoxin production in the fungus. Signal transduction via G protein signalling pathways represents one mechanism by which oxylipin signals might elicit these changes. Therefore, in this review we integrate discussion of oxylipin signals and of G protein signalling cascades as regulators of fungal development.
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Affiliation(s)
- Marion Brodhagen
- Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Dr, Madison, WI 53706-1598, USA
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Lubertozzi D, Keasling JD. Marker and promoter effects on heterologous expression in Aspergillus nidulans. Appl Microbiol Biotechnol 2006; 72:1014-23. [PMID: 16699756 DOI: 10.1007/s00253-006-0368-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2006] [Revised: 01/29/2006] [Accepted: 02/05/2006] [Indexed: 10/24/2022]
Abstract
To study the effects of selection marker, promoter type, and copy number on heterologous expression in Aspergillus nidulans, strains were constructed with single- and multicopy plasmid integrations bearing a reporter gene (lacZ) under the control of either an inducible (alcA) or constitutive (gpdA) promoter and one of three Aspergillus nutritional marker genes (argB, trpC, or niaD). beta-Galactosidase activity in the transformants varied over three orders of magnitude, with the majority of levels in the range of 5x10(3)-1x10(4) U/mg. Significant differences in mean expression levels were found when comparing single-copy transformants with the same promoter but a different marker. Transformants with the argB marker had the highest average expression, approximately threefold over the trpC or niaD clones. For each promoter, maximal expression for the set was seen in the range of the single-copy clones, implying that increasing the copy number does not reliably increase expression in Aspergillus.
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Affiliation(s)
- David Lubertozzi
- Department of Chemical Engineering,, University of California, Berkeley, CA 94720, USA
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Abstract
The formation of highly polarized hyphae that grow by apical extension is a defining feature of the filamentous fungi. High-resolution microscopy and mathematical modeling have revealed the importance of the cytoskeleton and the Spitzenkorper (an apical vesicle cluster) in hyphal morphogenesis. However, the underlying molecular mechanisms remain poorly characterized. In this review, the pathways and functions known to be involved in polarized hyphal growth are summarized. A central theme is the notion that the polarized growth of hyphae is more complex than in yeast, though similar sets of core pathways are likely utilized. In addition, a model for the establishment and maintenance of hyphal polarity is presented. Key features of the model include the idea that polarity establishment is a stochastic process that occurs independent of internal landmarks. Moreover, the stabilization of nascent polarity axes may be the critical step that permits the emergence of a new hypha.
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Affiliation(s)
- Steven D Harris
- Plant Science Initiative and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68588, USA
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31
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Boyce KJ, Hynes MJ, Andrianopoulos A. The Ras and Rho GTPases genetically interact to co-ordinately regulate cell polarity during development in Penicillium marneffei. Mol Microbiol 2005; 55:1487-501. [PMID: 15720555 DOI: 10.1111/j.1365-2958.2005.04485.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Ras and Rho GTPases have been examined in a wide variety of eukaryotes and play varied and often overlapping roles in cell polarization and development. Studies in Saccharomyces cerevisiae and mammalian cells have defined some of the central activities of these GTPases. However, these paradigms do not explain the role of these proteins in all eukaryotes. Unlike yeast, but like more complex eukaryotes, filamentous fungi have Rac-like proteins in addition to Ras and Cdc42. To investigate the unique functions of these proteins and determine how they interact to co-ordinately regulate morphogenesis during growth and development we undertook a genetic analysis of GTPase function by generating double mutants of the Rho GTPases cflA and cflB and the newly isolated Ras GTPase rasA from the dimorphic pathogenic fungus, Penicillium marneffei. P. marneffei growth at 25 degrees C is as multinucleate, septate, branched hyphae which are capable of undergoing asexual development (conidiation), while at 37 degrees C, uninucleate pathogenic yeast cells which divide by fission are produced. Here we show that RasA (Ras) acts upstream of CflA (Cdc42) to regulate germination of spores and polarized growth of both hyphal and yeast cells, while also exhibiting CflA-independent activities. CflA (Cdc42) and CflB (Rac) co-ordinately control hyphal cell polarization despite also having unique roles in regulating conidial germination and polarized growth of yeast cells (CflA) and polarized growth of conidiophore cell types and hyphal branching (CflB).
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Affiliation(s)
- Kylie J Boyce
- Department of Genetics, University of Melbourne, Melbourne, Victoria, Australia 3010
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Shoji JY, Maruyama JI, Arioka M, Kitamoto K. Development of Aspergillus oryzae thiA promoter as a tool for molecular biological studies. FEMS Microbiol Lett 2005; 244:41-6. [PMID: 15727819 DOI: 10.1016/j.femsle.2005.01.014] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 12/27/2004] [Accepted: 01/07/2005] [Indexed: 11/18/2022] Open
Abstract
In filamentous fungi, the repertoire of promoters available for exogenous gene expression is limited. Here, we report the development and application of the thiamine-regulatable thiA promoter (PthiA) in Aspergillus oryzae as a tool for molecular biological studies. When PthiA was used to express the enhanced green fluorescent protein (EGFP) reporter, the fluorescence in the mycelia was either repressed or induced in the presence or absence of thiamine in the culture media, respectively. In addition, the expression level from the thiA promoter can be controlled by the concentration of external thiamine. Thiamine content in the media did not affect mycelial morphology, making the thiA promoter more useful compared with alcA and amyB promoters that depend on carbon source for regulation. Moreover, as the A. oryzae thiA promoter was also regulated by thiamine in A. nidulans, this promoter can be further applied as an inducible promoter in other Aspergilli.
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Affiliation(s)
- Jun-Ya Shoji
- Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
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Fortwendel JR, Panepinto JC, Seitz AE, Askew DS, Rhodes JC. Aspergillus fumigatus rasA and rasB regulate the timing and morphology of asexual development. Fungal Genet Biol 2004; 41:129-39. [PMID: 14732259 DOI: 10.1016/j.fgb.2003.10.004] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Expression of rasA plays an important role in conidial germination in Aspergillus nidulans. Conidial germination is required to initiate both infection and asexual development in the opportunistic pathogen Aspergillus fumigatus. Therefore, we sought to determine the requirements for Ras proteins in conidial germination and asexual development of A. fumigatus. A second homolog, rasB, has been identified that characterizes a new subclass of Ras genes. Dominant active (DA) and dominant negative (DN) mutations of each gene were introduced into protoplasts as transgenes. DArasA expression led to reduced conidiation, malformed conidiophores, and altered mitotic progression, whereas expression of DNrasA caused a significant reduction in the rate of conidial germination. In contrast, expression of DNrasB slightly delayed the initiation of germination and caused the development of conidiophores in submerged culture. DArasB expression led to reduced conidiation. RasA and RasB appear to play different, but overlapping, roles in the vegetative growth and asexual development of A. fumigatus.
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Affiliation(s)
- Jarrod R Fortwendel
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH 45267-0529, USA
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Shi X, Sha Y, Kaminskyj S. Aspergillus nidulans hypA regulates morphogenesis through the secretion pathway. Fungal Genet Biol 2004; 41:75-88. [PMID: 14643261 DOI: 10.1016/j.fgb.2003.09.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Aspergillus nidulans hypA encodes a predicted 1474 amino acid, 161.9 kDa cytoplasmic peptide. Strains with hypA1 and hypA6 alleles are wild type at 28 degrees C but have wide, slow-growing hyphae and thick walls at 42 degrees C. hypA1 and hypA6 have identical genetic lesions. hypA1 and hypA6 restrictive phenotypes have statistically similar morphometry, and strains with either allele can conidiate at 42 degrees C. hypA deletion strains require osmotic support and have aberrant morphology, but produce viable spores at 28 degrees C. hypA has full-length orthologs in filamentous fungi and yeasts and a 200 amino acid region with similarity to sequences in plants and animals. The Saccharomyces cerevisiae hypA ortholog is TRS120, a regulatory subunit in the TRAPP II complex that mediates traffic through the Golgi equivalent. Enzyme secretion is reduced in hypA1 cells at 42 degrees C. Endomembranes and cytoplasmic actin arrays in hypA1 have weak polarity at 42 degrees C and cytoplasmic microtubules have reduced number and normal distribution.
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Affiliation(s)
- Xianzong Shi
- Department of Biology, University of Saskatchewan, SK, S7N 5E2 Saskatoon, Canada
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35
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Abstract
Ras is a small monomeric GTP binding protein that transduces signals for growth and differentiation of eukaryotic organisms. Previously, a unique ras gene, designated Ct-ras, was cloned from the alfalfa fungal phytopathogen, Colletotrichum trifolii. Expression of Ct-Ras in mouse fibroblast cells (NIH3T3) demonstrated that Ct-ras is functionally similar to the mammalian ras genes since activating mutations of Ct-ras caused oncogenic phenotypes in nu/nu mice, including tumors. In C. trifolii, activated 'oncogenic' Ras (Val2) induced abnormal hyphal proliferation, defects in polarized growth and significantly reduced differentiation such as conidiation and appressorium formation in a nutrient dependent manner. Gene disruption of ct-ras was lethal. To further evaluate the function of Ct-Ras in C. trifolii, three different approaches were used: overexpression of cytosolic Ras by CAAX box deletion; expression of dominant negative Ct-RasT22N; and antisense ct-ras expression. Results showed that suppression of Ct-Ras activity significantly decreases fungal germination frequencies and hyphal growth rates. Taken together, these data suggest involvement of Ct-Ras in regulation of fungal cell growth and differentiation.
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Affiliation(s)
- Young-sil Ha
- Department of Plant Pathology, University of Nebraska, 406G Plant Science Hall, Lincoln, NE 68583-0722, USA
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Dou X, Wu D, An W, Davies J, Hashmi SB, Ukil L, Osmani SA. The PHOA and PHOB Cyclin-Dependent Kinases Perform an Essential Function in Aspergillus nidulans. Genetics 2003; 165:1105-15. [PMID: 14668368 PMCID: PMC1462817 DOI: 10.1093/genetics/165.3.1105] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Unlike Pho85 of Saccharomyces cerevisiae, the highly related PHOA cyclin-dependent kinase (CDK) of Aspergillus nidulans plays no role in regulation of enzymes involved in phosphorous acquisition but instead modulates differentiation in response to environmental conditions, including limited phosphorous. Like PHO85, Aspergillus phoA is a nonessential gene. However, we find that expression of dominant-negative PHOA inhibits growth, suggesting it may have an essential but redundant function. Supporting this we have identified another cyclin-dependent kinase, PHOB, which is 77% identical to PHOA. Deletion of phoB causes no phenotype, even under phosphorous-limited growth conditions. To investigate the function of phoA/phoB, double mutants were selected from a cross of strains containing null alleles and by generating a temperature-sensitive allele of phoA in a ΔphoB background. Double-deleted ascospores were able to germinate but had a limited capacity for nuclear division, suggesting a cell cycle defect. Longer germination revealed morphological defects. The temperature-sensitive phoA allele caused both nuclear division and polarity defects at restrictive temperature, which could be complemented by expression of mammalian CDK5. Therefore, an essential function exists in A. nidulans for the Pho85-like kinase pair PHOA and PHOB, which may involve cell cycle control and morphogenesis.
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Affiliation(s)
- Xiaowei Dou
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43210, USA
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37
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Weeks G, Spiegelman GB. Roles played by Ras subfamily proteins in the cell and developmental biology of microorganisms. Cell Signal 2003; 15:901-9. [PMID: 12873703 DOI: 10.1016/s0898-6568(03)00073-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The Ras subfamily proteins are monomeric GTPases that function as molecular switches in cellular signal transduction pathways. This review describes our current knowledge of the roles that these proteins play in the growth and differentiation of single celled microorganisms.
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Affiliation(s)
- Gerald Weeks
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
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38
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Zuber S, Hynes MJ, Andrianopoulos A. The G-protein alpha-subunit GasC plays a major role in germination in the dimorphic fungus Penicillium marneffei. Genetics 2003; 164:487-99. [PMID: 12807770 PMCID: PMC1462590 DOI: 10.1093/genetics/164.2.487] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The opportunistic human pathogen Penicillium marneffei exhibits a temperature-dependent dimorphic switch. At 25 degrees, multinucleate, septate hyphae that can undergo differentiation to produce asexual spores (conidia) are produced. At 37 degrees hyphae undergo arthroconidiation to produce uninucleate yeast cells that divide by fission. This work describes the cloning of the P. marneffei gasC gene encoding a G-protein alpha-subunit that shows high homology to members of the class III fungal Galpha-subunits. Characterization of a DeltagasC mutant and strains carrying a dominant-activating gasC(G45R) or a dominant-interfering gasC(G207R) allele show that GasC is a crucial regulator of germination. A DeltagasC mutant is severely delayed in germination, whereas strains carrying a dominant-activating gasC(G45R) allele show a significantly accelerated germination rate. Additionally, GasC signaling positively affects the production of the red pigment by P. marneffei at 25 degrees and negatively affects the onset of conidiation and the conidial yield, showing that GasC function overlaps with functions of the previously described Galpha-subunit GasA. In contrast to the S. cerevisiae ortholog Gpa2, our data indicate that GasC is not involved in carbon or nitrogen source sensing and plays no major role in either hyphal or yeast growth or in the switch between these two forms.
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Affiliation(s)
- Sophie Zuber
- Department of Genetics, University of Melbourne, 3010 Victoria, Australia
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39
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Wheeler IE, Hollomon DW, Gustafson G, Mitchell JC, Longhurst C, Zhang Z, Gurr SJ. Quinoxyfen perturbs signal transduction in barley powdery mildew (Blumeria graminis f.sp. hordei). MOLECULAR PLANT PATHOLOGY 2003; 4:177-186. [PMID: 20569377 DOI: 10.1046/j.1364-3703.2003.00165.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
SUMMARY Quinoxyfen is a protectant fungicide which controls powdery mildew diseases by interfering with germination and/or appressorium formation. Mutants of barley powdery mildew, Blumeria graminis f.sp. hordei, which are resistant to quinoxyfen produce fewer conidia, which germinate and form appressoria more promiscuously than do the prolific numbers of wild-type spores. This suggests that resistance bypasses host recognition signals. RT-PCR profiles of signal transduction genes, recorded during wild-type germling morphogenesis, reveals that quinoxyfen alters the accumulation of Protein Kinase C (pkc), pkc-like and catalytic subunit of Protein Kinase A (cpka) transcripts. Differential display-reverse transcription PCR identified a gene transcript in wild-type conidia that was absent, or much less abundant, in conidia from quinoxyfen-resistant mutants. This mRNA was not detectable 24 h after wild-type conidia were inoculated on to barley. It encodes a GTPase activating protein (GAP), which may interact with a small molecular weight Ras-type GTP binding protein. In the presence of quinoxyfen, the gap mRNA remains throughout germling morphogenesis. The involvement of GAP in resistance suggests that quinoxyfen inhibits mildew infection by disrupting early cell signalling events.
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Affiliation(s)
- Ian E Wheeler
- IACR-Long Ashton Research Station, Department of Agricultural Science, University of Bristol, Long Ashton, Bristol, BS41 9AF, UK
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40
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Vanzela APDFC, Said S. Evidence for carbon source regulated protein kinase A and protein kinase C signaling in the duplication cycle, polarization and septum formation in Aspergillus nidulans. Microbiol Res 2003; 157:239-47. [PMID: 12398295 DOI: 10.1078/0944-5013-00156] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The effects of glucose and of a pectic substrate in the duplication cycle, spore polarization and septation of Aspergillus nidulans were tested in poor and rich media. Growth on poor conditions and on sodium polypectate slowed nuclear duplication and reduced the coupling of polarization to mitosis. Coupling of septation to the third mitosis was also reduced by changing growth conditions. When protein kinase A (PKA) and protein kinase C (PKC) activators were added to the media the results suggested a role for PKA in slowing the duplication cycle, while allowing polarization. Addition of a PKC activator to poor media uncoupled the first septum formation from the third mitosis in a carbon source-regulated manner, suggesting a role for PKC in coordinating cell cycle signals, growth and cytokinesis.
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41
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Jin Y, Bok JW, Guzman-de-Peña D, Keller NP. Requirement of spermidine for developmental transitions in Aspergillus nidulans. Mol Microbiol 2002; 46:801-12. [PMID: 12410837 DOI: 10.1046/j.1365-2958.2002.03201.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Deletion of the spermidine synthase gene in the fungus Aspergillus nidulans results in a strain, deltaspdA, which requires spermidine for growth and accumulates putrescine as the sole polyamine. Vegetative growth but not sporulation or sterigmatocystin production is observed when deltaspdA is grown on media supplemented with 0.05-0.10 mM exogenous spermidine. Supplementation of deltaspdA with >/= 0.10 mM spermidine restores sterigmatocystin production and >/= 0.50 mM spermidine produces a phenotype with denser asexual spore production and decreased radial hyphal growth compared with the wild type. DeltaspdA spores germinate in unsupplemented media but germ tube growth ceases after 8 h upon which time the spores swell to approximately three times their normal diameter. Hyphal growth is resumed upon addition of 1.0 mM spermidine. Suppression of a G protein signalling pathway could not force asexual sporulation and sterigmatocystin production in deltaspdA strains grown in media lacking spermidine but could force both processes in deltaspdA strains supplemented with 0.05 mM spermidine. These results show that increasing levels of spermidine are required for the transitions from (i) germ tube to hyphal growth and (ii) hyphal growth to tissue differentiation and secondary metabolism. Suppression of G protein signalling can over-ride the spermidine requirement for the latter but not the former transition.
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Affiliation(s)
- Yuan Jin
- Department of Plant Pathology, Texas A & M University, College Station, TX 77843-2132, USA
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42
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Firon A, Beauvais A, Latgé JP, Couvé E, Grosjean-Cournoyer MC, D'Enfert C. Characterization of essential genes by parasexual genetics in the human fungal pathogen Aspergillus fumigatus: impact of genomic rearrangements associated with electroporation of DNA. Genetics 2002; 161:1077-87. [PMID: 12136012 PMCID: PMC1462181 DOI: 10.1093/genetics/161.3.1077] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We have evaluated the usefulness of parasexual genetics in the identification of genes essential for the growth of the human fungal pathogen Aspergillus fumigatus. First, essentiality of the A. fumigatus AfFKS1 gene, encoding the catalytic subunit of the beta-(1,3)-glucan synthase complex, was assessed by inactivating one allele of AfFKS1 in a diploid strain of A. fumigatus obtained using adequate selectable markers in spore color and nitrate utilization pathways and by performing haploidization under conditions that select for the occurrence of the disrupted allele. Haploid progeny could not be obtained, demonstrating that AfFKS1 and, hence, beta-(1,3)-glucan synthesis are essential in A. fumigatus. Second, random heterozygous insertional mutants were generated by electroporation of diploid conidia with a heterologous plasmid. A total of 4.5% of the transformants failed to produce haploid progeny on selective medium. Genomic analysis of these heterozygous diploids led in particular to the identification of an essential A. fumigatus gene encoding an SMC-like protein resembling one in Schizosacccharomyces pombe involved in chromosome condensation and cohesion. However, significant plasmid and genomic DNA rearrangements were observed at many of the identified genomic loci where plasmid integration had occurred, thus suggesting that the use of electroporation to build libraries of A. fumigatus insertional mutants has relatively limited value and cannot be used in an exhaustive search of essential genes.
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Affiliation(s)
- Arnaud Firon
- Unité Microbiologie et Environnement, CNRS URA 2172, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France
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43
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Fillinger S, Chaveroche MK, Shimizu K, Keller N, d'Enfert C. cAMP and ras signalling independently control spore germination in the filamentous fungus Aspergillus nidulans. Mol Microbiol 2002; 44:1001-16. [PMID: 12046590 DOI: 10.1046/j.1365-2958.2002.02933.x] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The role of cAMP signalling during germination of asexual spores (conidia) of the filamentous fungus Aspergillus nidulans was investigated. A. nidulans strains defective for adenylate cyclase (CyaA) or for the functionally overlapping cAMP-dependent protein kinase (PkaA) and newly characterized SchA protein kinase, homologous to Saccharomyces cerevisiae Sch9, show altered trehalose mobilization and kinetics of germ tube outgrowth, in addition to other defects in colony formation. cAMP-dependent trehalose breakdown is triggered by the addition of a carbon source independently of further catabolism, suggesting that cAMP signalling controls early events of conidial germination in response to carbon source sensing. Additional results suggest that cAMP has targets other than PkaA and SchA and that PkaA retains activity in the absence of cAMP. Conversely, PkaA regulates cAMP levels in A. nidulans because these are elevated by approximately 250-fold in a strain that lacks PkaA. Furthermore, analysis of mutant strains impaired in both adenylate cyclase and RasA GTPase previously implicated in the control of A. nidulans spore germination suggested that RasA and cAMP signalling proceed independently during germination in A. nidulans.
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Affiliation(s)
- Sabine Fillinger
- Unité Microbiologie et Environnement, CNRS URA 2172, Institut Pasteur, Paris, France
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44
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Ichinomiya M, Motoyama T, Fujiwara M, Takagi M, Horiuchi H, Ohta A. Repression of chsB expression reveals the functional importance of class IV chitin synthase gene chsD in hyphal growth and conidiation of Aspergillus nidulans. MICROBIOLOGY (READING, ENGLAND) 2002; 148:1335-47. [PMID: 11988507 DOI: 10.1099/00221287-148-5-1335] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The functions of two previously identified chitin synthase genes in Aspergillus nidulans, chsB and chsD, were analysed. First, a conditional chsB mutant was constructed in which the expression of chsB is under the control of a repressible promoter, the alcA promoter, of A. nidulans. Under repressing conditions, the mutant grew slowly and produced highly branched hyphae, supporting the idea that chsB is involved in normal hyphal growth. The involvement of chsB in conidiation was also demonstrated. Next, double mutants of chsB and chsD were constructed, in which chsB was placed under the control of the alcA promoter and chsD was replaced with the argB gene of A. nidulans. These double mutants grew more slowly than the chsB single mutant under high-osmolarity conditions. The hyphae of the double mutant appeared to be more disorganized than those of the chsB single mutant. It was also found that ChsD was functionally implicated in conidiation when the expression of chsB was limited. These results indicate the importance of the ChsD function in the absence of chsB expression. The roles of ChsB and ChsD in hyphal growth and in conidiation were supported by the analysis of the spatial expression patterns of chsB and chsD, using lacZ of Escherichia coli as a reporter gene.
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Affiliation(s)
- Masayuki Ichinomiya
- Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
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45
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Abstract
Fungi generally display either of two growth modes, yeast-like or filamentous, whereas dimorphic fungi, upon environmental stimuli, are able to switch between the yeast-like and the filamentous growth mode. Signal transduction pathways have been elucidated in the budding yeast Saccharomyces cerevisiae, establishing a morphogenetic network that links cell-cycle events with cellular morphogenesis. Recent molecular genetic studies in several filamentous fungal model systems revealed key components required for distinct steps from fungal spore germination to the maintenance of polar hyphal growth, mycelium formation, and nuclear division. This allows a mechanistic comparison of yeast-like and hyphal growth and the establishment of a core model morphogenetic network for filamentous growth including signaling via the cAMP pathway, Rho modules, and cell cycle kinases. Appreciating similarities between morphogenetic networks of the unicellular yeasts and the multicellular filamentous fungi will open new research directions, help in isolating the central network components, and ultimately pave the way to elucidate the central differences (of many) that distinguish, e.g., the growth mode of filamentous fungi from that of their yeast-like relatives, the role of cAMP signaling, and nuclear division.
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Affiliation(s)
- J Wendland
- Department of Microbiology, Friedrich-Schiller University, Jena, D-07745, Germany
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46
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Leberer E, Harcus D, Dignard D, Johnson L, Ushinsky S, Thomas DY, Schröppel K. Ras links cellular morphogenesis to virulence by regulation of the MAP kinase and cAMP signalling pathways in the pathogenic fungus Candida albicans. Mol Microbiol 2001; 42:673-87. [PMID: 11722734 DOI: 10.1046/j.1365-2958.2001.02672.x] [Citation(s) in RCA: 230] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The pathogenic fungus Candida albicans is capable of responding to a wide variety of environmental cues with a morphological transition from a budding yeast to a polarized filamentous form. We demonstrate that the Ras homologue of C. albicans, CaRas1p, is required for this morphological transition and thereby contributes to the development of pathogenicity. However, CaRas1p is not required for cellular viability. Deletion of both alleles of the CaRAS1 gene caused in vitro defects in morphological transition that were reversed by either supplementing the growth media with cAMP or overexpressing components of the filament-inducing mitogen-activated protein (MAP) kinase cascade. The induction of filament-specific secreted aspartyl proteinases encoded by the SAP4-6 genes was blocked in the mutant cells. The defects in filament formation were also observed in situ after phagocytosis of C. albicans cells in a macrophage cell culture assay and, in vivo, after infection of kidneys in a mouse model for systemic candidiasis. In the macrophage assay, the mutant cells were less resistant to phagocytosis. Moreover, the defects in filament formation were associated with reduced virulence in the mouse model. These results indicate that, in response to environmental cues, CaRas1p is required for the regulation of both a MAP kinase signalling pathway and a cAMP signalling pathway. CaRas1p-dependent activation of these pathways contributes to the pathogenicity of C. albicans cells through the induction of polarized morphogenesis. These findings elucidate a new medically relevant role for Ras in cellular morphogenesis and virulence in an important human infectious disease.
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Affiliation(s)
- E Leberer
- Eukaryotic Genetics Group, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, Quebec H4P 2R2, Canada.
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47
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Abstract
The asexual spore, or conidium, is critical in the life cycle of many fungi because it is the primary means for dispersion and serves as a 'safe house' for the fungal genome in adverse environmental conditions. This review discusses the physiological process of germination, conidial adhesion and initiation of protein synthesis and also the regulatory pathways used to activate conidial germination. These include Ca(2+)/calmodulin-mediated signaling, the cyclic AMP/protein kinase A and the ras/mitogen-activated protein kinase pathways. Insights into the process of conidial germination will increase our understanding of the mechanisms of dormancy and sensing of environmental stimuli, and permit identification of novel therapeutic targets for the treatment of spore-borne fungal infections in plants and animals.
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Affiliation(s)
- N Osherov
- Division of Pathology and Laboratory Medicine, P.O. Box 54, The University of Texas, M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
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48
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Sundaram S, Kim SJ, Suzuki H, Mcquattie CJ, Hiremah ST, Podila GK. Isolation and characterization of a symbiosis-regulated ras from the ectomycorrhizal fungus Laccaria bicolor. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:618-28. [PMID: 11332726 DOI: 10.1094/mpmi.2001.14.5.618] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Ectomycorrhizae formed by the symbiotic interaction between ectomycorrhizal fungi and plant roots play a key role in maintaining and improving the health of a wide range of plants. Mycorrhizal initiation, development, and functional maintenance involve morphological changes that are mediated by activation and suppression of several fungal and plant genes. We identified a gene, Lbras, in the ectomycorrhizal fungus Laccaria bicolor that belongs to the ras family of genes, which has been shown in other systems to be associated with signaling pathways controlling cell growth and proliferation. The Lbras cDNA complemented ras2 function in Saccharomyces cerevisiae and had the ability to transform mammalian cells. Expression of Lbras, present as a single copy in the genome, was dependent upon interaction with host roots. Northern analysis showed that expression was detectable in L bicolor 48 h after interaction as well as in the established mycorrhizal tissue. Phylogenetic analysis with other Ras proteins showed that Lbras is related most closely to Aras of Aspergillus nidulans.
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Affiliation(s)
- S Sundaram
- Department of Biological Sciences, Michigan Technological University, Houghton 49931, USA
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49
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Shimizu K, Keller NP. Genetic involvement of a cAMP-dependent protein kinase in a G protein signaling pathway regulating morphological and chemical transitions in Aspergillus nidulans. Genetics 2001; 157:591-600. [PMID: 11156981 PMCID: PMC1461531 DOI: 10.1093/genetics/157.2.591] [Citation(s) in RCA: 353] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In the filamentous fungus Aspergillus nidulans, a heterotrimeric G protein alpha-subunit and an RGS domain protein, encoded by fadA and flbA, respectively, regulate production of the carcinogenic metabolite sterigmatocystin (ST) and asexual spores (i.e., conidia). We investigated the genetic involvement of the cAMP-dependent protein kinase catalytic subunit (PkaA), a potential downstream target of FadA activity, in ST production and conidiation. Relative to wild type, sporulation was decreased in the pkaA overexpression strain but was not totally absent, as occurs in DeltaflbA or fadA(G42R) (fadA-dominant active) strains. Deletion of pkaA resulted in a hyper-conidiating strain with limited radial growth. This phenotype was epistatic to mutation in flbA or fadA; the double mutants DeltapkaA; DeltaflbA and DeltapkaA; fadA(G42R) recovered sporulation and their radial growth was severely restricted. PkaA overexpression also negatively regulated AflR, the ST biosynthesis-specific transcription factor, both transcriptionally and post-transcriptionally. Deletion of pkaA restored ST production in the DeltaflbA background but not in the fadA(G42R) background. These data provide genetic evidence that the FlbA/FadA signaling pathway regulating ST production and morphological development is partially mediated through PkaA.
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Affiliation(s)
- K Shimizu
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132, USA
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Wendland J, Philippsen P. Cell polarity and hyphal morphogenesis are controlled by multiple rho-protein modules in the filamentous ascomycete Ashbya gossypii. Genetics 2001; 157:601-10. [PMID: 11156982 PMCID: PMC1461536 DOI: 10.1093/genetics/157.2.601] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Polarized cell growth requires a polarized organization of the actin cytoskeleton. Small GTP-binding proteins of the Rho-family have been shown to be involved in the regulation of actin polarization as well as other processes. Hyphal growth in filamentous fungi represents an ideal model to investigate mechanisms involved in generating cell polarity and establishing polarized cell growth. Since a potential role of Rho-proteins has not been studied so far in filamentous fungi we isolated and characterized the Ashbya gossypii homologs of the Saccharomyces cerevisiae CDC42, CDC24, RHO1, and RHO3 genes. The AgCDC42 and AgCDC24 genes can both complement conditional mutations in the S. cerevisiae CDC42 and CDC24 genes and both proteins are required for the establishment of actin polarization in A. gossypii germ cells. Agrho1 mutants show a cell lysis phenotype. Null mutant strains of Agrho3 show periodic swelling of hyphal tips that is overcome by repolarization and polar hyphal growth in a manner resembling the germination pattern of spores. Thus different Rho-protein modules are required for distinct steps during polarized hyphal growth of A. gossypii.
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Affiliation(s)
- J Wendland
- Lehrstuhl für Angewandte Mikrobiologie, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
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