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A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

ABSTRACT: Chitin is an important fungal cell wall component that is cross-linked to β-glucan for structural integrity. Acquisition of chitin to glucan cross-links has previously been shown to be performed by transglycosylation enzymes in S. cerevisiae, called Congo Red hypersensitive (Crh) enzymes. Here, we characterized the impact of deleting all seven gene members of the crh gene family (crhA-G) in Aspergillus niger on cell wall integrity, cell wall composition and genome-wide gene expression. In this study, we show that the seven-fold knockout strain shows slightly compact plate growth, but no increased sensitivity to cell wall perturbing compounds. Additionally, we found that the cell wall composition of this knockout strain was virtually identical to that of the wild type. In congruence with these data, genome-wide expression analysis revealed very limited changes in gene expression and no signs of activation of the cell wall integrity response pathway. However, deleting the entire crh gene family in cell wall mutants that are deficient in either galactofuranose (ΔugmA) or α-glucan (ΔagsE and ΔagsA, ΔagsE), resulted in a synthetic growth defect and an increased sensitivity towards Congo Red compared the parental strains. Altogether, these results indicate that loss of the crh gene family in A. niger does not trigger the cell wall integrity response in itself, but does play an important role in ensuring cell wall integrity in mutant strains with reduced galactofuranose or α-glucan.

ORGANISM(S): Aspergillus niger

PROVIDER: GSE142461 | GEO | 2019/12/21

REPOSITORIES: GEO

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THE CAPACITY OF ASPERGILLUS NIGER TO SENSE AND RESPOND TO CELL WALL STRESS REQUIRES AT LEAST THREE TRANSCRIPTION FACTORS: RLMA, MSNA AND CRZA

Project description:Transcriptomics signatures of Aspergillus niger were used to predict regulator proteins mediating the survival responses against these stressors and the phenotypes of selected null mutant strains were studied. This integrated approach allowed us to reconstruct a model for the cell wall salvage gene network of A. niger that ensures survival of the fungus upon cell surface stress. The model predicts that (i) caspofungin and aureobasidin A induce the cell wall integrity pathway as main compensatory response including RhoB, RhoD, MkkA and RlmA as regulator proteins. (ii) RlmA is the main transcription factor required for the protection against calcofluor white but cooperates with MsnA and CrzA to ensure survival of A. niger when challenged with caspofungin or aureobasidin A. All three transcription factors are important for these compensatory responses and involve induction of glucan and chitin synthesising genes amongst others. (iii) Membrane stress provoked by aureobasidin A via disturbance of sphingolipid synthesis induces cell wall stress in A. niger, but membrane stress provoked by fenpropimorph via disturbance of ergosterol synthesis does not. The present work uncovered different defence strategies of A. niger to protect itself against cell wall stress conditions. At least three transcription factors - RlmA, MsnA and CrzA – are employed in a well-balanced manner. The data also predicts a fourth transfactor, SrbA, which seems to be specifically important during fenpropimorph-induced cell membrane stress. Future studies will disclose how these regulators are interlocked in different signalling pathways to secure survival of A. niger under different cell wall stress conditions.

2014-12-31 | GSE56471 | GEO

Re-masking of fungal cell wall PAMPs in response to environmental pH is regulated by multiple processes

Project description:Candida albicans is a commensal yeast of the human gut, which is tolerated by the immune system, but has the potential to become an opportunistic pathogen. One way in which C. albicans achieves this duality is through the concealing, or exposure of cell wall associated pathogen-associated molecular patterns (PAMPs) in response to host derived environment cues (pH, hypoxia, lactate). This cell wall remodelling allows C. albicans to evade or hyperactivate the host’s innate immune responses leading to disease. Previously we identified that adaptation of C. albicans to acidic environments, conditions encountered during colonisation of the female reproductive tract, induce significant cell wall remodelling resulting in the exposure of two key fungal PAMPs (glucan and chitin). Here we report that this pH-dependent cell wall remodelling is a highly dynamic process, requiring periods of both cell wall unmasking, with peak PAMP exposure occurring between 2-4 hrs, followed by subsequent PAMP remasking. b-glucan remasking was mediated via the cell density dependent fungal quorum sensing molecule farnesol, while chitin remasking was mediated via a small, heat-stable, non-proteinaceous secreted molecule(s). Transcript profiling identified a core set of 42 genes significantly regulated by pH over time, and linked the transcription factor Efg1p to being the main regulator of chitin exposure through regulation of CHT2. This dynamic cell wall remodelling, influenced innate immune recognition of C. albicans, suggesting that during infection C. albicans can manipulate the host innate immune responses.

2019-10-16 | GSE130948 | GEO

A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

Project description:A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

| PRJNA597061 | ENA

Deletion of the Aspergillus niger pro-protein processing protease gene kexB results in a pH-dependent morphological transition during submerged cultivations and increases cell wall chitin content

Project description:There is a growing interest for the use of post-fermentation mycelial waste to obtain cell wall chitin as an added-value product. In the pursuit to identify suitable production strains that can be used for post-fermentation cell wall harvesting, we turned to an Aspergillus niger strain in which the kexB (also named pclA in literature) gene was deleted. Previous work has shown that deletion of kexB causes hyper-branching and thicker cell walls, which is beneficial as these properties reduce fermentation viscosity and lysis. The deletion of kexB has been shown to exhibit a pH-dependent hyper-branching on solid agar plates at pH 6.0, but not at pH 5.0, whereas this phenotype was reported to be less pronounced during submerged growth. Here, we show a series of controlled batch cultivations performed at a pH range of 5, 5.5, and 6 to examine the pellet phenotype in liquid medium of the ΔkexB strain. Morphological analysis showed that the ΔkexB formed wild type-like pellets at pH 5.0 whereas the characteristic hyper-branching ΔkexB phenotype was found at pH 6.0. Cultivations at pH 5.5 showed that the ΔkexB strain grows as an intermediate phenotype of pH 5.0 and pH 6.0. Analyzing the cell walls of the ΔkexB strain from these controlled pH-conditions showed an increase in chitin content compared to wild type at all three pH values tested. Surprisingly, the increase in chitin content was found to be irrespective of the hyper-branching morphology. Evidence for alterations in cell wall make-up are corroborated by transcriptional analysis that showed a significant cell wall stress response in addition to upregulation of genes encoding other unrelated cell well biosynthetic genes.

2020-06-26 | GSE151618 | GEO

Epitope shaving and fungal immune evasion – cell wall proteomes

Project description:The cell wall provides a major physical interface between fungal pathogens and their mammalian host. This extracellular armour is critical for fungal cell homeostasis and survival. Yet essential cell wall moieties, such as β-1,3-glucan, are recognised as pathogen-associated molecular patterns (PAMPs) that activate immune-mediated clearance mechanisms. We have reported that the opportunistic human fungal pathogen, Candida albicans, masks β-1,3-glucan following exposure to lactate, hypoxia or iron depletion. However, the precise mechanism(s) by which C. albicans masks β-1,3-glucan have remained obscure. Here, we performed proteomic analysis of cell walls from C. albicans cells grown in hypoxia or lactate compared to glucose-grown controls to identify mechanisms driving β-1,3-glucan masking.

2020-06-15 | PXD018027 | Pride

Deletion of the celA gene in Aspergillus nidulans triggers overexpression of secondary metabolite biosynthetic genes

Project description:The cell wall is a structure involved in important stages of fungal growth and morphogenesis. Several studies in the literature have shown how perturbations at the cell wall-level trigger dramatic effects on growth (e.g. Horiuchi, 2009). Despite the importance of fungal cell walls and despite the great advances made in the field, there are still missing pieces in our understanding of cell wall dynamics in filamentous fungi. Some cell wall biosynthetic genes, for example, are still uncharacterized (for a detailed inventory of Aspergillus nidulans cell wall-related genes, see de Groot et al., 2009). The chief polysaccharides in the cell wall of the model organism A. nidulans are β-glucans (β-1,3-, β-(1,3;1,4)- and β-1,6-glucans), chitin and α-1,3-glucans. While much is known about the chitin and α-1,3-glucan biosynthetic genes in A. nidulans (Horiuchi et al., 1999; Fujiwara et al., 2000; Ichinomiya et al., 2002 and 2005; Takeshita et al., 2006; Yoshimi et al., 2013), no characterization is yet available for the celA gene (ANIA_08444) encoding a putative mixed-linkage glucan synthase (de Groot et al., 2009). Recently, a study on A. fumigatus has characterized Tft1, an enzyme shown to be responsible for the production of β-(1,3;1,4)-glucans in this organism (Samar et al., 2015). Deletion of Tft1 causes no obvious phenotype in A. fumigatus and a modest increase in virulence. To characterize the role of β-(1,3;1,4)-glucans in the growth and development of filamentous fungi, we here sought to provide transcriptomics data of an A. nidulans strain showing reduced expression of the gene encoding the putative mixed linkage glucan synthase celA.

2017-07-26 | GSE94110 | GEO

The transcriptional repressor TupA in Aspergillus niger is involved in controlling gene expression related to cell wall biosynthesis, development, and nitrogen source availability

Project description:The Tup1-Cyc8 (Ssn6) complex is a well characterized and conserved general transcriptional repressor complex in eukaryotic cells. Here, we report the identification of the Tup1 (TupA) homolog in the filamentous fungus Aspergillus niger in a genetic screen for mutants with a constitutive expression of the agsA gene. The agsA gene encodes a putative alpha-glucan synthase, which is induced in response to cell wall stress in A niger. Apart from the constitutive expression of agsA, the selected mutant was also found to produce an unknown pigment at high temperatures. Complementation analysis with a genomic library showed that the tupA gene could complement the phenotypes of the mutant. Screening of a collection of 240 mutants with constitutive expression of agsA identified sixteen additional pigment-secreting mutants, which were all mutated in the tupA gene. The phenotypes of the tupA mutants were very similar to the phenotypes of a tupA deletion strain. Further analysis of the tupA-17 mutant and the ΔtupA mutant revealed that TupA is also required for normal growth and morphogenesis. The production of the pigment at 37ºC is nitrogen source-dependent and repressed by ammonium. Genome-wide expression analysis of the tupA mutant during exponential growth revealed derepression of a large group of diverse genes, including genes related to development and cell wall biosynthesis, and also protease-encoding genes that are normally repressed by ammonium. Comparison of the transcriptome of up-regulated genes in the tupA mutant showed limited overlap with the transcriptome of caspofungin-induced cell wall stress-related genes, suggesting that TupA is not a general suppressor of cell wall stress-induced genes. We propose that TupA is an important repressor of genes related to development and nitrogen metabolism.

2013-12-31 | GSE50523 | GEO

Integrated post-genomic cell wall analysis reveals floating biofilm formation associated with high expression of flocculins in the pathogen Candida krusei.

Project description:The pathogenic yeast Candida krusei is more distantly related to Candida albicans than clinically relevant CTG-clade Candida species. Its cell wall, a dynamic organelle that is the first point of interaction between pathogen and host, is relatively understudied, and its wall proteome remains unidentified to date. Here, we present an integrated study of the cell wall in C. krusei. Our comparative genomic studies and experimental data indicate that the general structure of the cell wall in C. krusei is similar to Saccharomyces cerevisiae and C. albicans and is comprised of b-1,3-glucan, b-1,6-glucan, chitin, and mannoproteins. However, some pronounced differences with C. albicans walls were observed, for instance, higher mannan and protein levels and altered protein mannosylation patterns. Further, despite absence of proteins with high sequence similarity to Candida adhesins, protein structure modeling identified eleven proteins with similarity to flocculins/adhesins in S. cerevisiae or C. albicans. To obtain a proteomic comparison of biofilm and planktonic cells, C. krusei cells were grown to exponential phase and in static 24-h cultures. Interestingly, the 24-h static cultures of C. krusei yielded formation of floating biofilm (flor) rather than adherence to polystyrene at the bottom. The proteomic analysis of both conditions identified a total of 32 cell wall proteins. In line with a possible role in flor formation, increased abundance of flocculins, in particular Flo110, was observed in the floating biofilm compared to exponential cells. This study is the first to provide a detailed description of the cell wall in C. krusei including its cell wall proteome, and paves the way for further investigations on the importance of flor formation and flocculins in the pathogenesis of C. krusei.

2023-04-25 | MSV000091793 | MassIVE

human gut metagenome

Project description:FiberTAG Chitin-glucan

| PRJNA636138 | ENA

Functional control of the Candida albicans cell wall by catalytic protein kinase A subunit Tpk1

Project description:The cyclic AMP-protein kinase A pathway has a central role in the biology of Candida albicans, a prominent fungal pathogen of humans. The two catalytic subunits for cyclic AMP-dependent protein kinase, Tpk1 (orf19.4892) and Tpk2 (orf19.2277), have divergent roles, and most studies indicate a more pronounced role for Tpk2. Here we dissect two Tpk1-responsive properties: adherence and cell wall integrity. Homozygous tpk1/tpk1 mutants are hyperadherent, and a Tpk1 defect enables biofilm formation in the absence of Bcr1, a central transcriptional regulator of biofilm adhesins. Microarray analysis revealed an enrichment for cell wall and surface functions among Tpk1-repressed genes, and overexpression of individual target genes indicates that cell surface proteins Als1, Als2, Als4, Csh1, and Csp37 contribute to Tpk1-regulated adherence. Tpk1 is also required for cell wall integrity, but has no role in the cell wall integrity gene expression response. Interestingly, increased expression of the adhesin gene ALS2 conferred a cell wall defect, as manifested in hypersensitivity to the cell wall inhibitor caspofungin and a shallow cell wall structure. Our findings indicate that Tpk1 has a central role in C. albicans cell wall properties that is exerted through repression of select cell surface protein genes.

2012-08-07 | GSE38846 | GEO

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