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1.
β-1,3-Glucan and chitin are the most prominent polysaccharides of the fungal cell wall. Covalently linked, these polymers form a scaffold that determines the form and properties of vegetative and pathogenic hyphae. While the role of chitin in plant infection is well understood, the role of β-1,3-glucan is unknown. We functionally characterized the β-1,3-glucan synthase gene GLS1 of the maize (Zea mays) pathogen Colletotrichum graminicola, employing RNA interference (RNAi), GLS1 overexpression, live-cell imaging, and aniline blue fluorochrome staining. This hemibiotroph sequentially differentiates a melanized appressorium on the cuticle and biotrophic and necrotrophic hyphae in its host. Massive β-1,3-glucan contents were detected in cell walls of appressoria and necrotrophic hyphae. Unexpectedly, GLS1 expression and β-1,3-glucan contents were drastically reduced during biotrophic development. In appressoria of RNAi strains, downregulation of β-1,3-glucan synthesis increased cell wall elasticity, and the appressoria exploded. While the shape of biotrophic hyphae was unaffected in RNAi strains, necrotrophic hyphae showed severe distortions. Constitutive expression of GLS1 led to exposure of β-1,3-glucan on biotrophic hyphae, massive induction of broad-spectrum defense responses, and significantly reduced disease symptom severity. Thus, while β-1,3-glucan synthesis is required for cell wall rigidity in appressoria and fast-growing necrotrophic hyphae, its rigorous downregulation during biotrophic development represents a strategy for evading β-glucan–triggered immunity. 相似文献
2.
Thomas Stalhberger Catherine Simenel Cécile Clavaud Vincent G. H. Eijsink Roland Jourdain Muriel Delepierre Jean-Paul Latgé Lionel Breton Thierry Fontaine 《The Journal of biological chemistry》2014,289(18):12647-12656
Malassezia species are ubiquitous residents of human skin and are associated with several diseases such as seborrheic dermatitis, tinea versicolor, folliculitis, atopic dermatitis, and scalp conditions such as dandruff. Host-Malassezia interactions and mechanisms to evade local immune responses remain largely unknown. Malassezia restricta is one of the most predominant yeasts of the healthy human skin, its cell wall has been investigated in this paper. Polysaccharides in the M. restricta cell wall are almost exclusively alkali-insoluble, showing that they play an essential role in the organization and rigidity of the M. restricta cell wall. Fractionation of cell wall polymers and carbohydrate analyses showed that the polysaccharide core of the cell wall of M. restricta contained an average of 5% chitin, 20% chitosan, 5% β-(1,3)-glucan, and 70% β-(1,6)-glucan. In contrast to other yeasts, chitin and chitosan are relatively abundant, and β-(1,3)-glucans constitute a minor cell wall component. The most abundant polymer is β-(1,6)-glucans, which are large molecules composed of a linear β-(1,6)-glucan chains with β-(1,3)-glucosyl side chain with an average of 1 branch point every 3.8 glucose unit. Both β-glucans are cross-linked, forming a huge alkali-insoluble complex with chitin and chitosan polymers. Data presented here show that M. restricta has a polysaccharide organization very different of all fungal species analyzed to date. 相似文献
3.
Antonella Torosantucci Paola Chiani Carla Bromuro Flavia De Bernardis Angelina S. Palma Yan Liu Giuseppina Mignogna Bruno Maras Marisa Colone Annarita Stringaro Silvia Zamboni Ten Feizi Antonio Cassone 《PloS one》2009,4(4)
Anti-β-glucan antibodies elicited by a laminarin-conjugate vaccine confer cross-protection to mice challenged with major fungal pathogens such as Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. To gain insights into protective β-glucan epitope(s) and protection mechanisms, we studied two anti-β-glucan monoclonal antibodies (mAb) with identical complementarity-determining regions but different isotypes (mAb 2G8, IgG2b and mAb 1E12, IgM). C. albicans, the most relevant fungal pathogen for humans, was used as a model.Both mAbs bound to fungal cell surface and to the β1,3-β1,6 glucan of the fungal cell wall skeleton, as shown by immunofluorescence, electron-microscopy and ELISA. They were also equally unable to opsonize fungal cells in a J774 macrophage phagocytosis and killing assay. However, only the IgG2b conferred substantial protection against mucosal and systemic candidiasis in passive vaccination experiments in rodents. Competition ELISA and microarray analyses using sequence-defined glucan oligosaccharides showed that the protective IgG2b selectively bound to β1,3-linked (laminarin-like) glucose sequences whereas the non-protective IgM bound to β1,6- and β1,4-linked glucose sequences in addition to β1,3-linked ones. Only the protective IgG2b recognized heterogeneous, polydisperse high molecular weight cell wall and secretory components of the fungus, two of which were identified as the GPI-anchored cell wall proteins Als3 and Hyr1. In addition, only the IgG2b inhibited in vitro two critical virulence attributes of the fungus, hyphal growth and adherence to human epithelial cells.Our study demonstrates that the isotype of anti-β-glucan antibodies may affect details of the β-glucan epitopes recognized, and this may be associated with a differing ability to inhibit virulence attributes of the fungus and confer protection in vivo. Our data also suggest that the anti-virulence properties of the IgG2b mAb may be linked to its capacity to recognize β-glucan epitope(s) on some cell wall components that exert critical functions in fungal cell wall structure and adherence to host cells. 相似文献
4.
The Role of Glucosidase I (Cwh41p) in the Biosynthesis of Cell Wall β-1,6-Glucan Is Indirect
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CWH41, a gene involved in the assembly of cell wall β-1,6-glucan, has recently been shown to be the structural gene for Saccharomyces cerevisiae glucosidase I that is responsible for initiating the trimming of terminal α-1,2-glucose residue in the N-glycan processing pathway. To distinguish between a direct or indirect role of Cwh41p in the biosynthesis of β-1,6-glucan, we constructed a double mutant, alg5Δ (lacking dolichol-P-glucose synthase) cwh41Δ, and found that it has the same phenotype as the alg5Δ single mutant. It contains wild-type levels of cell wall β-1,6-glucan, shows moderate underglycosylation of N-linked glycoproteins, and grows at concentrations of Calcofluor White (which interferes with cell wall assembly) that are lethal to cwh41Δ single mutant. The strong genetic interactions of CWH41 with KRE6 and KRE1, two other genes involved in the β-1,6-glucan biosynthetic pathway, disappear in the absence of dolichol-P-glucose synthase (alg5Δ). The triple mutant alg5Δcwh41Δkre6Δ is viable, whereas the double mutant cwh41Δkre6Δ in the same genetic background is not. The severe slow growth phenotype and 75% reduction in cell wall β-1,6-glucan, characteristic of the cwh41Δkre1Δ double mutant, are not observed in the triple mutant alg5Δcwh41Δkre1Δ. Kre6p, a putative Golgi glucan synthase, is unstable in cwh41Δ strains, and its overexpression renders these cells Calcofluor White resistant. These results demonstrate that the role of glucosidase I (Cwh41p) in the biosynthesis of cell wall β-1,6-glucan is indirect and that dolichol-P-glucose is not an intermediate in this pathway. 相似文献
5.
Vishukumar Aimanianda C��cile Clavaud Catherine Simenel Thierry Fontaine Muriel Delepierre Jean-Paul Latg�� 《The Journal of biological chemistry》2009,284(20):13401-13412
Despite its essential role in the yeast cell wall, the exact composition of
the β-(1,6)-glucan component is not well characterized. While
solubilizing the cell wall alkali-insoluble fraction from a wild type strain
of Saccharomyces cerevisiae using a recombinant
β-(1,3)-glucanase followed by chromatographic characterization of the
digest on an anion exchange column, we observed a soluble polymer that eluted
at the end of the solvent gradient run. Further characterization indicated
this soluble polymer to have a molecular mass of ∼38 kDa and could be
hydrolyzed only by β-(1,6)-glucanase. Gas chromatographymass spectrometry
and NMR (1H and 13C) analyses confirmed it to be a
β-(1,6)-glucan polymer with, on average, branching at every fifth residue
with one or two β-(1,3)-linked glucose units in the side chain. This
polymer peak was significantly reduced in the corresponding digests from
mutants of the kre genes (kre9 and kre5) that are
known to play a crucial role in the β-(1,6)-glucan biosynthesis. In the
current study, we have developed a biochemical assay wherein incubation of
UDP-[14C]glucose with permeabilized S. cerevisiae yeasts
resulted in the synthesis of a polymer chemically identical to the branched
β-(1,6)-glucan isolated from the cell wall. Using this assay, parameters
essential for β-(1,6)-glucan synthetic activity were defined.The cell wall of Saccharomyces cerevisiae and other yeasts
contains two types of β-glucans. In the former yeast, branched
β-(1,3)-glucan accounts for ∼50–55%, whereas
β-(1,6)-glucan represents 10–15% of the total yeast cell wall
polysaccharides, each chain of the latter extending up to 140–350
glucose residues in length. The amount of 3,6-branched glucose residues varies
with the yeast species: 7, 15, and 75% in S. cerevisiae, Candida
albicans, and Schizosaccharomyces pombe, respectively
(1). β-(1,6)-Glucan
stabilizes the cell wall, since it plays a central role as a linker for
specific cell wall components, including β-(1,3)-glucan, chitin, and
mannoproteins (2,
3). However, the exact
structure of the β-(1,6)-glucan and the mode of biosynthesis of this
polymer are largely unknown. In S. pombe, immunodetection studies
suggested that synthesis of this polymer backbone begins in the endoplasmic
reticulum, with extension occurring in the Golgi
(4) and final processing at the
plasma membrane. In S. cerevisiae, Montijn and co-workers
(5), by immunogold labeling,
detected β-(1,6)-glucan at the plasma membrane, suggesting that the
synthesis takes place largely at the cell surface.More than 20 genes, including the KRE gene family (14 members) and
their homologues, SKN1 and KNH1, have been reported to be
involved in β-(1,6)-glucan synthesis in S. cerevisiae, C.
albicans, and Candida glabrata
(6–10).
Among all of these genes, the ones that seem to play the major synthetic role
are KRE5 and KRE9, since their disruption caused significant
reduction (100 and 80%, respectively, relative to wild type) in the cell wall
β-(1,6)-glucan content
(11–13).To date, the biochemical reaction responsible for the synthesis of
β-(1,6)-glucan and the product synthesized remained unknown. Indeed, in
most cases, when membrane preparations are incubated with UDP-glucose, only
linear β-(1,3)-glucan polymers are produced, although some studies have
reported the production of low amounts of β-(1,6)-glucans by membrane
preparations
(14–17).
These data suggest that disruption of the fungal cell prevents or at least has
a strong negative effect on β-(1,6)-glucan synthesis. The use of
permeabilized cells, which allows substrates, such as nucleotide sugar
precursors, to be readily transported across the plasma membrane, is an
alternative method to study in situ cell wall enzyme activities
(18–22).
A number of methods have been developed to permeabilize the yeast cell wall
(23), of which osmotic shock
was successfully used to demonstrate β-(1,3)-glucan and chitin synthase
activities (20,
24). Herein, we describe the
biochemical activity responsible for β-(1,6)-glucan synthesis using
permeabilized S. cerevisiae cells and UDP-[14C]glucose as
a substrate. We also have analyzed the physicochemical parameters of this
activity and chemically characterized the end product and its structural
organization within the mature yeast cell wall. 相似文献
6.
Hiroki Okada Shinsuke Ohnuki Cesar Roncero James B. Konopka Yoshikazu Ohya 《Molecular biology of the cell》2014,25(2):222-233
The cell wall of budding yeast is a rigid structure composed of multiple components. To thoroughly understand its involvement in morphogenesis, we used the image analysis software CalMorph to quantitatively analyze cell morphology after treatment with drugs that inhibit different processes during cell wall synthesis. Cells treated with cell wall–affecting drugs exhibited broader necks and increased morphological variation. Tunicamycin, which inhibits the initial step of N-glycosylation of cell wall mannoproteins, induced morphologies similar to those of strains defective in α-mannosylation. The chitin synthase inhibitor nikkomycin Z induced morphological changes similar to those of mutants defective in chitin transglycosylase, possibly due to the critical role of chitin in anchoring the β-glucan network. To define the mode of action of echinocandin B, a 1,3-β-glucan synthase inhibitor, we compared the morphology it induced with mutants of Fks1 that contains the catalytic domain for 1,3-β-glucan synthesis. Echinocandin B exerted morphological effects similar to those observed in some fks1 mutants, with defects in cell polarity and reduced glucan synthesis activity, suggesting that echinocandin B affects not only 1,3-β-glucan synthesis, but also another functional domain. Thus our multivariate analyses reveal discrete functions of cell wall components and increase our understanding of the pharmacology of antifungal drugs. 相似文献
7.
beta-1,3-Glucan in Developing Cotton Fibers: Structure, Localization, and Relationship of Synthesis to That of Secondary Wall Cellulose
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Evidence is presented for the existence of a noncellulosic β-1,3-glucan in cotton fibers. The glucan can be isolated as distinct fractions of varying solubility. When fibers are homogenized rigorously in aqueous buffer, part of the total β-1,3-glucan is found as a soluble polymer in homogenates freed of cell walls. The proportion of total β-1,3-glucan which is found as the soluble polymer varies somewhat as a function of fiber age. The insoluble fraction of the β-1,3-glucan remains associated with the cell wall fraction. Of this cell wall β-1,3-glucan, a variable portion can be solubilized by treatment of walls with hot water, a further portion can be solubilized by alkaline extraction of the walls, and 17 to 29% of the glucan remains associated with cellulose even after alkaline extraction. A portion of this glucan can also be removed from the cell walls of intact cotton fibers by digestion with an endo-β-1,3-glucanase. The glucan fraction which can be isolated as a soluble polymer in homogenates freed of cell walls is not associated with membranous material, and we propose that it represents glucan which is also extracellular but not tightly associated with the cell wall. Enzyme digestion studies indicate that all of the cotton fiber glucan is β-linked, and methylation analyses and enzyme studies both show that the predominant linkage in the glucan is 1 → 3. The possibility of some minor branching at C-6 can also be deduced from the methylation analyses. The timing of deposition of the β-1,3-glucan during fiber development coincides closely with the onset of secondary wall cellulose synthesis. Kinetic studies performed with ovules and fibers cultured in vitro show that incorporation of radioactivity from [14C]glucose into β-1,3-glucan is linear with respect to time almost from the start of the labeling period; however, a lag is observed before incorporation into cellulose becomes linear with time, suggesting that these two different glucans are not polymerized directly from the same substrate pool. Pulse-chase experiments indicate that neither the β-1,3-glucan nor cellulose exhibits significant turnover after synthesis. 相似文献
8.
9.
10.
11.
Altered extent of cross-linking of beta1,6-glucosylated mannoproteins to chitin in Saccharomyces cerevisiae mutants with reduced cell wall beta1,3-glucan content. 总被引:2,自引:0,他引:2
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J C Kapteyn A F Ram E M Groos R Kollar R C Montijn H Van Den Ende A Llobell E Cabib F M Klis 《Journal of bacteriology》1997,179(20):6279-6284
The yeast cell wall contains beta1,3-glucanase-extractable and beta1,3-glucanase-resistant mannoproteins. The beta1,3-glucanase-extractable proteins are retained in the cell wall by attachment to a beta1,6-glucan moiety, which in its turn is linked to beta1,3-glucan (J. C. Kapteyn, R. C. Montijn, E. Vink, J. De La Cruz, A. Llobell, J. E. Douwes, H. Shimoi, P. N. Lipke, and F. M. Klis, Glycobiology 6:337-345, 1996). The beta1,3-glucanase-resistant protein fraction could be largely released by exochitinase treatment and contained the same set of beta1,6-glucosylated proteins, including Cwp1p, as the B1,3-glucanase-extractable fraction. Chitin was linked to the proteins in the beta1,3-glucanase-resistant fraction through a beta1,6-glucan moiety. In wild-type cell walls, the beta1,3-glucanase-resistant protein fraction represented only 1 to 2% of the covalently linked cell wall proteins, whereas in cell walls of fks1 and gas1 deletion strains, which contain much less beta1,3-glucan but more chitin, beta1,3-glucanase-resistant proteins represented about 40% of the total. We propose that the increased cross-linking of cell wall proteins via beta1,6-glucan to chitin represents a cell wall repair mechanism in yeast, which is activated in response to cell wall weakening. 相似文献
12.
The wall proteome and the secretome of the fungal pathogen Candida albicans help it to thrive in multiple niches of the human body. Mass spectrometry has allowed researchers to study the dynamics of both subproteomes. Here, we discuss some major responses of the secretome to host-related environmental conditions. Three β-1,3-glucan-modifying enzymes, Mp65, Sun41, and Tos1, are consistently found in large amounts in culture supernatants, suggesting that they are needed for construction and expansion of the cell wall β-1,3-glucan layer and thus correlate with growth and might serve as diagnostic biomarkers. The genes ENG1, CHT3, and SCW11, which encode an endoglucanase, the major chitinase, and a β-1,3-glucan-modifying enzyme, respectively, are periodically expressed and peak in M/G1. The corresponding protein abundances in the medium correlate with the degree of cell separation during single-yeast-cell, pseudohyphal, and hyphal growth. We also discuss the observation that cells treated with fluconazole, or other agents causing cell surface stress, form pseudohyphal aggregates. Fluconazole-treated cells secrete abundant amounts of the transglucosylase Phr1, which is involved in the accumulation of β-1,3-glucan in biofilms, raising the question whether this is a general response to cell surface stress. Other abundant secretome proteins also contribute to biofilm formation, emphasizing the important role of secretome proteins in this mode of growth. Finally, we discuss the relevance of these observations to therapeutic intervention. Together, these data illustrate that C. albicans actively adapts its secretome to environmental conditions, thus promoting its survival in widely divergent niches of the human body. 相似文献
13.
Balakumaran Chandrasekar Alan Wanke Stephan Wawra Pia Saake Lisa Mahdi Nyasha Charura Miriam Neidert Gereon Poschmann Milena Malisic Meik Thiele Kai Stühler Murali Dama Markus Pauly Alga Zuccaro 《The Plant cell》2022,34(7):2765
Plant pathogenic and beneficial fungi have evolved several strategies to evade immunity and cope with host-derived hydrolytic enzymes and oxidative stress in the apoplast, the extracellular space of plant tissues. Fungal hyphae are surrounded by an inner insoluble cell wall layer and an outer soluble extracellular polysaccharide (EPS) matrix. Here, we show by proteomics and glycomics that these two layers have distinct protein and carbohydrate signatures, and hence likely have different biological functions. The barley (Hordeum vulgare) β-1,3-endoglucanase HvBGLUII, which belongs to the widely distributed apoplastic glycoside hydrolase 17 family (GH17), releases a conserved β-1,3;1,6-glucan decasaccharide (β-GD) from the EPS matrices of fungi with different lifestyles and taxonomic positions. This low molecular weight β-GD does not activate plant immunity, is resilient to further enzymatic hydrolysis by β-1,3-endoglucanases due to the presence of three β-1,6-linked glucose branches and can scavenge reactive oxygen species. Exogenous application of β-GD leads to enhanced fungal colonization in barley, confirming its role in the fungal counter-defensive strategy to subvert host immunity. Our data highlight the hitherto undescribed capacity of this often-overlooked EPS matrix from plant-associated fungi to act as an outer protective barrier important for fungal accommodation within the hostile environment at the apoplastic plant–microbe interface.A β-1,3;1,6-glucan decasaccharide released from the fungal matrix by an apoplastic host hydrolase contributes to plant immune suppression and fungal accommodation.IN A NUTSHELL Background: Plants secrete various hydrolytic enzymes into the apoplastic space to protect themselves against invading microbes. Some of these enzymes target the fungal cell wall polymer chitin. This enzymatic attack leads to the release of chitin oligomers, which can be perceived by the plant immune system, informing the plant to activate its defense machinery. However, chitin accounts for only a small part of most fungal cell walls. Recent studies have highlighted a largely uncharacterized, β-glucan-rich extracellular polysaccharide matrix (EPS) surrounding the cell wall of various plant-colonizing fungi. Question: This EPS matrix is made of glucose and abundantly produced during colonization. As its secretion into the extracellular environment is costly for the fungus, we explored how this EPS matrix affects plant immunity and fungal colonization. Findings: We demonstrated that EPS matrices from a symbiotic and pathogenic plant-colonizing fungus are distinct from the nonsoluble fungal cell walls with respect to their protein and carbohydrate composition. Enzymatic digests revealed that a secreted plant hydrolase from barley (HvBGLUII) acts on these EPS matrices and releases a highly branched β-glucan decasaccharide (β-GD) fragment. This fragment is not perceived by the plant immune system but instead detoxifies reactive oxygen species produced by the plant host as a defense mechanism and contributes to host colonization. We thus have shown that the outermost fungal EPS layer represents a protective shield against oxidative stress. Next steps: The diversity of linkage types and branching patterns of β-glucans not only accounts for their different biochemical properties, but also makes them important messengers for the plant, potentially encoding specific information on the approaching fungal invader. Future studies should aim to identify other plant hydrolases and the elusive glucan receptors, to disentangle the contribution of β-glucans to the communication between plant hosts and fungi. 相似文献
14.
Luciano Polonelli Concetta Beninati Giuseppe Teti Franco Felici Tecla Ciociola Laura Giovati Martina Sperindè Carla Lo Passo Ida Pernice Maria Domina Milena Arigò Salvatore Papasergi Giuseppe Mancuso Stefania Conti Walter Magliani 《PloS one》2014,9(8)
A mouse anti-anti-anti-idiotypic (Id) IgM monoclonal antibody (mAb K20, Ab4), functionally mimicking a Wyckerhamomyces anomalus (Pichia anomala) killer toxin (KT) characterized by fungicidal activity against yeasts presenting specific cell wall receptors (KTR) mainly constituted by β-1,3-glucan, was produced from animals presenting anti-KT Abs (Ab3) following immunization with a rat IgM anti-Id KT-like mAb (mAb K10, Ab2). MAb K10 was produced by immunization with a KT-neutralizing mAb (mAb KT4, Ab1) bearing the internal image of KTR. MAb K20, likewise mAb K10, proved to be fungicidal in vitro against KT-sensitive Candida albicans cells, an activity neutralized by mAb KT4, and was capable of binding to β-1,3-glucan. MAb K20 and mAb K10 competed with each other and with KT for binding to C. albicans KTR. MAb K20 was used to identify peptide mimics of KTR by the selection of phage clones from random peptide phage display libraries. Using this strategy, four peptides (TK 1-4) were selected and used as immunogen in mice in the form of either keyhole limpet hemocyanin (KLH) conjugates or peptide-encoding minigenes. Peptide and DNA immunization could induce serum Abs characterized by candidacidal activity, which was inhibited by laminarin, a soluble β-1,3-glucan, but not by pustulan, a β-1,6-glucan. These findings show that the idiotypic cascade can not only overcome the barrier of animal species but also the nature of immunogens and the type of technology adopted. 相似文献
15.
Aspergillus fumigatus is an environmental mold that causes severe, often fatal invasive infections in immunocompromised patients. The search for new antifungal drug targets is critical, and the synthesis of the cell wall represents a potential area to find such a target. Embedded within the main β-1,3-glucan core of the A. fumigatus cell wall is a mixed linkage, β-D-(1,3;1,4)-glucan. The role of this molecule or how it is synthesized is unknown, though it comprises 10% of the glucans within the wall. While this is not a well-studied molecule in fungi, it has been studied in plants. Using the sequences of two plant mixed linkage glucan synthases, a single ortholog was identified in A. fumigatus (Tft1). A strain lacking this enzyme (tft1Δ) was generated along with revertant strains containing the native gene under the control of either the native or a strongly expressing promoter. Immunofluorescence staining with an antibody against β-(1,3;1,4)-glucan and biochemical quantification of this polysaccharide in the tft1Δ strain demonstrated complete loss of this molecule. Reintroduction of the gene into the knockout strain yielded reappearance in amounts that correlated with expected expression of the gene. The loss of Tft1 and mixed linkage glucan yielded no in vitro growth phenotype. However, there was a modest increase in virulence for the tft1Δ strain in a wax worm model. While the precise roles for β-(1,3;1,4)-glucan within A. fumigatus cell wall are still uncertain, it is clear that Tft1 plays a pivotal role in the biosynthesis of this cell wall polysaccharide. 相似文献
16.
Takashi Fujikawa Ayumu Sakaguchi Yoko Nishizawa Yusuke Kouzai Eiichi Minami Shigekazu Yano Hironori Koga Tetsuo Meshi Marie Nishimura 《PLoS pathogens》2012,8(8)
Plants evoke innate immunity against microbial challenges upon recognition of pathogen-associated molecular patterns (PAMPs), such as fungal cell wall chitin. Nevertheless, pathogens may circumvent the host PAMP-triggered immunity. We previously reported that the ascomycete Magnaporthe oryzae, a famine-causing rice pathogen, masks cell wall surfaces with α-1,3-glucan during invasion. Here, we show that the surface α-1,3-glucan is indispensable for the successful infection of the fungus by interfering with the plant''s defense mechanisms. The α-1,3-glucan synthase gene MgAGS1 was not essential for infectious structure development but was required for infection in M. oryzae. Lack or degradation of surface α-1,3-glucan increased fungal susceptibility towards chitinase, suggesting the protective role of α-1,3-glucan against plants'' antifungal enzymes during infection. Furthermore, rice plants secreting bacterial α-1,3-glucanase (AGL-rice) showed strong resistance not only to M. oryzae but also to the phylogenetically distant ascomycete Cochlioborus miyabeanus and the polyphagous basidiomycete Rhizoctonia solani; the histocytochemical analysis of the latter two revealed that α-1,3-glucan also concealed cell wall chitin in an infection-specific manner. Treatment with α-1,3-glucanase in vitro caused fragmentation of infectious hyphae in R. solani but not in M. oryzae or C. miyabeanus, indicating that α-1,3-glucan is also involved in maintaining infectious structures in some fungi. Importantly, rapid defense responses were evoked (a few hours after inoculation) in the AGL-rice inoculated with M. oryzae, C. miyabeanus and R. solani as well as in non-transgenic rice inoculated with the ags1 mutant. Taken together, our results suggest that α-1,3-glucan protected the fungal cell wall from degradative enzymes secreted by plants even from the pre-penetration stage and interfered with the release of PAMPs to delay innate immune defense responses. Because α-1,3-glucan is nondegradable in plants, it is reasonable that many fungal plant pathogens utilize α-1,3-glucan in the innate immune evasion mechanism and some in maintaining the structures. 相似文献
17.
The release of soluble carbohydrates from isolated cell wall of maize (Zea mays L.) was investigated in the range of pH 1 to 8.5. The pH profile demonstrated two peaks, a broad peak at pH 6 due to enzymatic breakdown of β-glucan to monosaccharides (wall autolysis) and a sharp peak at pH 2.5 due to acid-mediated, nonenzymatic liberation of macromolecular β-glucan from the wall. The pH dependence of acid-induced growth and cell-wall extensibility of coleoptile segments closely agrees with the pH dependence of acid-mediated β-glucan solubilization in the isolated wall. However, there is no evidence that enzymatic or nonenzymatic β-glucan solubilization is involved in the mechanism of auxin-mediated growth. 相似文献
18.
Peter Orlean 《Genetics》2012,192(3):775-818
The wall gives a Saccharomyces cerevisiae cell its osmotic integrity; defines cell shape during budding growth, mating, sporulation, and pseudohypha formation; and presents adhesive glycoproteins to other yeast cells. The wall consists of β1,3- and β1,6-glucans, a small amount of chitin, and many different proteins that may bear N- and O-linked glycans and a glycolipid anchor. These components become cross-linked in various ways to form higher-order complexes. Wall composition and degree of cross-linking vary during growth and development and change in response to cell wall stress. This article reviews wall biogenesis in vegetative cells, covering the structure of wall components and how they are cross-linked; the biosynthesis of N- and O-linked glycans, glycosylphosphatidylinositol membrane anchors, β1,3- and β1,6-linked glucans, and chitin; the reactions that cross-link wall components; and the possible functions of enzymatic and nonenzymatic cell wall proteins. 相似文献
19.
Fission Yeast Rgf2p Is a Rho1p Guanine Nucleotide Exchange Factor Required for Spore Wall Maturation and for the Maintenance of Cell Integrity in the Absence of Rgf1p
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Patricia García Ignacio García Flix Marcos Gorka Ruiz de Garibay Yolanda Snchez 《Genetics》2009,181(4):1321-1334
Schizosaccharomyces pombe Rho1p is essential, directly activates β-1,3-glucan synthase, and participates in the regulation of morphogenesis. In S. pombe, Rho1p is activated by at least three guanine nucleotide exchange factors (GEFs): Rgf1p, Rgf2p, and Rgf3p. In this study we show that Rgf2p is a Rho1p GEF required for sporulation. The rgf2+ deletion did not affect forespore membrane formation and the nuclei were encapsulated properly. However, the mutant ascospores appeared dark and immature. The rgf2Δ zygotes were not able to release the ascospores spontaneously, and the germination efficiency was greatly reduced compared to wild-type (wt) spores. This phenotype resembles that of the mutants in bgs2+, which encodes a sporulation-specific glucan synthase subunit. In fact, glucan synthase activity was diminished in sporulating rgf2Δ diploids. Rgf2p also plays a role in β-glucan biosynthesis during vegetative growth. Overexpression of rgf2+ specifically increased GTP-bound Rho1p, caused changes in cell morphology, and elicited an increase in β-1,3-glucan synthase activity. Moreover, the simultaneous disruption of rgf1+ and rgf2+ was lethal and both Rgf1p and Rgf2p were able to partially substitute for each other. Our results suggest that Rgf1p and Rgf2p are alternative GEFs with an essential overlapping function in Rho1p activation during vegetative growth. 相似文献
20.
β-Glucans are the main components of the fungal cell wall. Fission yeast possesses a family of β-glucan synthase-related genes. We describe here the cloning and characterization of bgs3+, a new member of this family. bgs3+ was cloned as a suppressor of a mutant hypersensitive to Echinocandin and Calcofluor White, drugs that interfere with cell wall biosynthesis. Disruption of the gene is lethal, and a decrease in Bgs3p levels leads to rounded cells with thicker walls, slightly reduces the amount of the β-glucan, and raises the amount of α-glucan polymer. These cells finally died. bgs3+ is expressed in vegetative cells grown in different conditions and during mating and germination and is not enhanced by stress situations. Consistent with the observed expression pattern, Bgs3-green fluorescence protein (GFP-Bgs3p) was found at the growing tips during interphase and at the septum prior to cytokinesis, always localized to growth areas. We also found GFP-Bgs3p in mating projections, during the early stages of zygote formation, and at the growing pole during ascospore germination. We conclude that Bgs3p localization is restricted to growth areas and that Bgs3p is a glucan synthase homologue required for cell wall biosynthesis and cell elongation in the fission yeast life cycle. 相似文献