Actin has multiple roles in the formation and architecture of zoospores of the oomycetes, Saprolegnia ferax and Achlya bisexualis

1992 ◽  
Vol 102 (3) ◽  
pp. 611-627 ◽  
Author(s):  
I. BRENT HEATH ◽  
RUTH L. HAROLD
Keyword(s):  
Cell Wall ◽  
Germ Tube ◽  
Multiple Roles ◽  
Rhodamine Phalloidin ◽  
Saprolegnia Ferax ◽  
Functional Changes ◽  
Specific Effects ◽  
Changing Patterns ◽  
Microtubular Root ◽  
Achlya Bisexualis

Very similar changing patterns of actin are described with rhodamine-phalloidin labelling during the zoosporic life cycle of the oomycetes, Saprolegnia ferax and Achlya bisexualis. By comparing the changes with previously described ultrastructural and functional changes, we show that actin functions in numerous previously unrecognized processes. Most spectacularly, the directed vesicle expansions of the cytokinetic system involve newly formed actin which outlines the developing zoospores. Disruption of this actin with cytochalasins leads to abnormal cleavage as witnessed by the formation of enlarged and irregular cysts. Prior to cytokinesis, two new types of organelle are synthesized and one, known as K bodies, clusters around the nuclei. These organdies are actin-rich during development and clustering, consistent with actin functioning in their positioning. In the zoospores, actin is concentrated around the water expulsion vacuoles, indicating that they are contractile, and permeates the cytoplasm, probably with a skeletal role. This concept is supported by the first demonstration of actin specifically associated with a microtubular root in the secondary zoospore. Upon encystment there is a dramatic increase in stained actin in the form of peripheral plaques associated with the newly synthesized cell wall. When the cysts germinate, a fibrillar actin cap, comparable to that previously described in hyphal tips, forms in the germ tube apex, but only after cell wall softening to permit germ tube protrusion. This sequence is consistent with the actin cap modulating turgor-driven expansion of the tip as previously discussed for hyphae. In addition to disrupting cleavage-associated actin, cytochalasins show developmental stage, dose and drug (CE≥CD≥CB) specific effects on zoosporulation-related actin, which indicates that, contrary to previous suggestions, rhodamine-phalloidin staining is a useful indicator of actin behaviour in response to cytochalasins. These responses include differential effects on adjoining actin arrays, some of which are transient in the continued presence of the drugs, indicating a mechanism of drug adaptation.

The Candida albicans pH-regulated KER1 gene encodes a lysine/glutamic-acid-rich plasma-membrane protein that is involved in cell aggregation

Microbiology ◽  
2004 ◽  
Vol 150 (8) ◽  
pp. 2641-2651 ◽  
Author(s):  
Amparo Galán ◽  
Manuel Casanova ◽  
Amelia Murgui ◽  
Donna M. MacCallum ◽  
Frank C. Odds ◽  
...  
Keyword(s):  
Cell Wall ◽  
Candida Albicans ◽  
Plasma Membrane ◽  
Glutamic Acid ◽  
Germ Tube ◽  
Cell Surface Hydrophobicity ◽  
Cell Aggregation ◽  
Surface Hydrophobicity ◽  
Amino Acid Sequences ◽  
Calcofluor White

Immunoscreening of a Candida albicans cDNA library with a polyclonal germ-tube-specific antibody (pAb anti-gt) resulted in the isolation of a gene encoding a lysine/glutamic-acid-rich protein, which was consequently designated KER1. The nucleotide and deduced amino acid sequences of this gene displayed no significant homology with any other known sequence. KER1 encodes a 134 kDa lysine (14·5 %)/glutamic acid (16·7 %) protein (Ker1p) that contains two potential transmembrane segments. KER1 was expressed in a pH-conditional manner, with maximal expression at alkaline pH and lower expression at pH 4·0, and was regulated by RIM101. A Δker1/Δker1 null mutant grew normally but was hyperflocculant under germ-tube-inducing conditions, yet this behaviour was also observed in stationary-phase cells grown under other incubation conditions. Western blotting analysis of different subcellular fractions, using as a probe a monospecific polyclonal antibody raised against a highly antigenic domain of Ker1p (pAb anti-Ker1p), revealed the presence of a 134 kDa band in the purified plasma-membrane fraction from the wild-type strain that was absent in the homologous preparation from Δker1/Δker1 mutant. The pattern of cell-wall protein and mannoprotein species released by digestion with β-glucanases, reactive towards pAbs anti-gt and anti-Ker1p, as well as against concanavalin A, was also different in the Δker1/Δker1 mutant. Mutant strains also displayed an increased cell-surface hydrophobicity and sensitivity to Congo red and Calcofluor white. Overall, these findings indicate that the mutant strain was affected in cell-wall composition and/or structure. The fact that the ker1 mutant had attenuated virulence in systemic mouse infections suggests that this surface protein is also important in host–fungus interactions.

Tapetal development and abiotic stress: a centre of vulnerability

2012 ◽  
Vol 39 (7) ◽  
pp. 553 ◽  
Author(s):  
Roger W. Parish ◽  
Huy A. Phan ◽  
Sylvana Iacuone ◽  
Song F. Li
Keyword(s):  
Cell Wall ◽  
Abiotic Stress ◽  
Oryza Sativa L ◽  
Triticum Aestivum L ◽  
Pollen Abortion ◽  
Cell Wall Invertase ◽  
Developmental Program ◽  
Specific Effects ◽  
Hexose Sugars ◽  
Microspore Stage

Many self-fertilising crops are particularly sensitive to abiotic stress at the reproductive stage. In rice (Oryza sativa L.) and wheat (Triticum aestivum L.), for example, abiotic stress during meiosis and the young microspore stage indicates the tapetum is highly vulnerable and that the developmental program appears to be compromised. Tapetal hypertrophy can occur as a consequence of cold and drought stress, and programmed cell death (PCD) is delayed or inhibited. Since the correct timing of tapetal PCD is essential for pollen reproduction, substantial losses in grain yield occur. In wheat and rice, a decrease in tapetal cell wall invertase levels is correlated with pollen abortion and results in the amount of hexose sugars reaching the tapetum, and subsequently the developing microspores, being severely reduced (‘starvation hypothesis’). ABA and gibberellin levels may be modified by cold and drought, influencing levels of cell wall invertase(s) and the tapetal developmental program, respectively. Many genes regulating tapetal and microspore development have been identified in Arabidopsis thaliana (L.) Heynh. and rice and the specific effects of abiotic stresses on the program and pathways can now begin to be assessed.

Protoplast Formation from Submerged Mycelium and from Spore Germinants of Streptomyces coelicolor

1985 ◽  
Vol 38 (1) ◽  
pp. 175 ◽  
Author(s):  
I Stevenson
Keyword(s):  
Cell Wall ◽  
Mycelial Growth ◽  
Germ Tube ◽  
Streptomyces Coelicolor ◽  
Cross Wall ◽  
Cellular Organization ◽  
Protoplast Formation ◽  
Cellular Compartment ◽  
Transmission Electron ◽  
Single Region

Stages in the formation of protoplasts from S. coelicolor strain A3(2) have been studied by transmission electron microscopy. Protoplasts liberated from submerged mycelial growth were variable in size and were released when digestion of the cell wall by lysozyme had completely or almost completely taken place. Protoplasts did not fully adopt the typical rounded shape until after release. A single region of cytoplasm gave rise to more than one protoplast unit. Protoplasts released from spore germinants escaped from the tip of the germ tube, which was the region of the cell wall most susceptible to digestion. Protoplasts derived from spore germinants were more consistent in size and rounded up more rapidly. If a cross-wall had formed in a germinant then it gave rise to separate protoplasts from each cellular. compartment. Protoplasts of either type contained a single DNA region. These studies give an indication of the cellular organization of a streptomycete colony, which can be visualized as a multinucleated assemblage of cellular units in a common cytoplasm. The assembly of units separates into a number of protoplasts on digestion of the cell wall.

Diverse organizations of actin and nuclei underpin the evolution of indeterminate growth in Chytridiomycota and Dikarya

Botany ◽  
2021 ◽  
Author(s):  
Jaclyn Marie Dee ◽  
Mary Berbee
Keyword(s):  
Cell Wall ◽  
Light Microscopy ◽  
Somatic Growth ◽  
Nuclear Migration ◽  
Nuclear Staining ◽  
Nuclear Positioning ◽  
Indeterminate Growth ◽  
Rhodamine Phalloidin ◽  
Actin Organization ◽  
Cell Wall Remodeling

Indeterminate growth, as in the hyphae of the “Humongous Fungus” of Michigan requires sustained nuclear migration and cell wall remodeling. We compare actin organization and patterns of nuclear positioning among four distantly related, indeterminate species of phylum Chytridiomycota: Cladochytrium replicatum, Physocladia obscura, Nowakowskiella sp., and Polychytrium aggregatum. We combined light microscopy, nuclear staining with DAPI, and actin staining with rhodamine phalloidin to analyze actin distribution and nuclear migration during somatic growth in the four Chytridiomycota species. Actin formed plaques, filaments, cables and perinuclear shells in patterns that varied across the four species. All four species initiated indeterminate growth by extending branching, anucleate rhizomycelium, <1 µm in diameter. Nuclei, some elongated as if migrating, first appear in intercalary segments that widened to diameters >1 µm. After mitosis, an intercalary swelling in C. replicatum became septate and a single, distal nucleus migrated tipwards to a new swelling. In Physocladia obscura, swellings were aseptate and multinucleate, and several nuclei migrated tipwards into a new swelling. Nuclei migrated tipwards from irregularly cylindrical filaments in Nowakowskiella sp., and in Polychytrium aggregatum, from regular, hypha-like filaments. Thus, distantly related lineages of zoosporic fungi deploy ancestral morphogenetic machinery in differing patterns that resulted in convergent, indeterminate growth.

Ultrastructure of basidiospore germination in Fomes fomentarius

1978 ◽  
Vol 56 (22) ◽  
pp. 2865-2872 ◽  
Author(s):  
Ichiko Tsuneda ◽  
Lorene L. Kennedy
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Germ Tube ◽  
Early Stage ◽  
Dense Layer ◽  
Lipid Bodies ◽  
Fomes Fomentarius ◽  
Additional Cell ◽  
Thin Electron ◽  
Germ Tubes

Germination of basidiospores in Fomes fomentarius (Fries) Kickx is bipolar with germ tubes emerging at both ends. Ungerminated spores are smooth with a thick cell wall consisting of two layers: an outer thin, electron-dense layer and an inner thick, electron-light layer. During the early stage of germination, two additional cell wall layers are formed: a very thin, electron-dense layer and a relatively thick, electron-light layer. Germ tube walls originate from these newly formed, inner layers. Ungerminated spores are uninucleate and contain numerous lipid bodies, ribosomes, and cisternae of endoplasmic reticulum. Germinated spores have distinct mitochondria and an invaginated plasma membrane and are usually devoid of endoplasmic reticulum.

An endophytic chitinase-producing isolate of Actinoplanes missouriensis, with potential for biological control of root rot of lupin caused by Plectosporium tabacinum

2003 ◽  
Vol 51 (3) ◽  
pp. 257 ◽  
Author(s):  
Khaled A. El-Tarabily
Keyword(s):  
Biological Control ◽  
Cell Wall ◽  
Root Rot ◽  
Germ Tube ◽  
First Record ◽  
Plant Roots ◽  
Wild Type ◽  
Type Isolate ◽  
Cell Wall Lysis

Twenty-one streptomycete and 15 non-streptomycete actinomycetes were isolated from surface-disinfested lupin roots and evaluated for their potential to produce chitinase and to inhibit the growth of Plectosporium tabacinum, the causal agent of lupin root rot in Egypt. The most inhibitory isolate was identified as Actinoplanes missouriensis which produced relatively high levels of chitinase and degraded the hyphae of P.�tabacinum in vitro, causing extensive plasmolysis and cell-wall lysis. A crude culture filtrate of A. missouriensis exhibited antifungal activity and significantly (P < 0.05) reduced spore germination and germ-tube growth of the pathogen. The antagonist was recovered from inside the root at all samplings up to 8 weeks after inoculation, indicating that the roots of healthy lupin may be a habitat for the endophyte. A. missouriensis significantly (P < 0.05) reduced the severity of root rot under glasshouse conditions. An endophytic isolate of Actinoplanes italicus incapable of producing chitinase and a mutant strain of A. missouriensis that did not produce detectable levels of chitinase, did not lyse hyphae of P. tabacinum or reduce root rot in the glasshouse experiments, although colonisation of the lupin root by both these isolates was similar to that of the chitinase-producing wild-type isolate of A. missouriensis. This study is the first record of control of a soil-borne plant pathogen by a chitinolytic actinomycete, endophytic in plant roots.

scholarly journals Disrupting progression of the yeast Hsp90 folding pathway at different transition points results in client-specific maturation defects

Genetics ◽  
2021 ◽  
Author(s):  
Kaitlyn Hohrman ◽  
Davi Gonçalves ◽  
Kevin A Morano ◽  
Jill L Johnson
Keyword(s):  
Heat Shock Protein 90 ◽  
Multiple Roles ◽  
Folding Pathway ◽  
Temperature Sensitive ◽  
Growth Defects ◽  
Specific Effects ◽  
Client Proteins ◽  
Transition Points ◽  
Mechanistic Basis

Abstract The protein molecular chaperone Hsp90 (Heat shock protein, 90 kilodalton) plays multiple roles in the biogenesis and regulation of client proteins impacting myriad aspects of cellular physiology. Amino acid alterations located throughout Saccharomyces cerevisiae Hsp90 have been shown to result in reduced client activity and temperature-sensitive growth defects. Although some Hsp90 mutants have been shown to affect activity of particular clients more than others, the mechanistic basis of client-specific effects is unknown. We found that Hsp90 mutants that disrupt the early step of Hsp70 and Sti1 interaction, or show reduced ability to adopt the ATP-bound closed conformation characterized by Sba1 and Cpr6 interaction, similarly disrupt activity of three diverse clients, Utp21, Ssl2, and v-src. In contrast, mutants that appear to alter other steps in the folding pathway had more limited effects on client activity. Protein expression profiling provided additional evidence that mutants that alter similar steps in the folding cycle cause similar in vivo consequences. Our characterization of these mutants provides new insight into how Hsp90 and cochaperones identify and interact with diverse clients, information essential for designing pharmaceutical approaches to selectively inhibit Hsp90 function.

scholarly journals A Monoclonal Antibody Directed against a Candida albicans Cell Wall Mannoprotein Exerts Three Anti-C. albicans Activities

2003 ◽  
Vol 71 (9) ◽  
pp. 5273-5279 ◽  
Author(s):  
María D. Moragues ◽  
Miren J. Omaetxebarria ◽  
Natalia Elguezabal ◽  
María J. Sevilla ◽  
Stefania Conti ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Cell Wall ◽  
Candida Albicans ◽  
Molecular Mass ◽  
Cryptococcus Neoformans ◽  
Germ Tube ◽  
Biological Activities ◽  
Killer Toxin ◽  
Pichia Anomala ◽  
Wide Range

ABSTRACT Antibodies are believed to play a role in the protection against Candida albicans infections by a number of mechanisms, including the inhibition of adhesion or germ tube formation, opsonization, neutralization of virulence-related enzymes, and direct candidacidal activity. Although some of these biological activities have been demonstrated individually in monoclonal antibodies (MAbs), it is not clear if all these anti-C. albicans activities can be displayed by a single antibody. In this report, we characterized a monoclonal antibody raised against the main target of salivary secretory immunoglobulin A in the cell wall of C. albicans, which exerts three anti-C. albicans activities: (i) inhibition of adherence to HEp-2 cells, (ii) inhibition of germination, and (iii) direct candidacidal activity. MAb C7 reacted with a proteinic epitope from a mannoprotein with a molecular mass of >200 kDa predominantly expressed on the C. albicans germ tube cell wall surface as well as with a number of antigens from Candida lusitaniae, Cryptococcus neoformans, Aspergillus fumigatus, and Scedosporium prolificans. MAb C7 caused a 31.1% inhibition in the adhesion of C. albicans to HEp-2 monolayers and a 55.3% inhibition in the adhesion of C. albicans to buccal epithelial cells, produced a 38.5% decrease in the filamentation of C. albicans, and exhibited a potent fungicidal effect against C. albicans, C. lusitaniae, Cryptococcus neoformans, A. fumigatus, and S. prolificans, showing reductions in fungal growth ranging from 34.2 to 88.7%. The fungicidal activity showed by MAb C7 seems to be related to that reported by antibodies mimicking the activity of a killer toxin produced by the yeast Pichia anomala, since one of these MAbs also reacted with the C. albicans mannoprotein with a molecular mass of >200 kDa. Results presented in this study support the concept of a family of microbicidal antibodies that could be useful in the treatment of a wide range of microbial infections when used alone or in combination with current antimicrobial agents.

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