In budding yeast cells, secretory vesicles and other organelles are only transported along actin cables, whilst—in contrast to the situation in hyphae—microtubules are restricted to just playing a role in nuclear positioning, spindle formation, and the segregation of chromosomes during nuclear division. Nuclei divide across the motherbud neck i.
Yeast cell septa are complete i. Bud scars remain on the surfaces of yeast cells following p. These are formed by budding yeast cells remaining attached after cytokinesis and becoming elongated. Subsequent budding of these attached cells results in highly branched structures with constrictions between each cell Figure 4. Mechanical agitation easily disrupts the attachment between pseudohyphal cells Berman ; Veses and Gow ; Sudbery The ability to exhibit dimorphic switching between a yeast and a hyphal growth form Figure 4.
Furthermore, during infection, C. Histoplasma, Blastomyces and Paracoccidioides produce only yeast cells at 37 o C and thus are the sole vegetative cells involved in human infection Boyce and Andrianopoulos ; Gauthier The Cryptococcus capsule and extracellular vesicles. Cryptococcus is another very important human fungal pathogen that grows inside the host as budding yeast cells.
The main characteristic feature of yeast cells of Cryptococcus is the formation of a polysaccharide capsule around a melanized cell wall Figure 4. The capsule grows in size within the host and is considered to be the main virulence factor of C. The complex capsule polysaccharide is synthesized within the cell and is then transported by means of extracellular vesicles through the cell wall to the capsule surface. Fungal extracellular vesicles were first discovered in C. It is becoming increasingly clear that extracellular vesicles are part of a general mechanism of macromolecule export by yeast cells and hyphae.
They can have a varied cargo, including nucleic acids, toxins, lipoproteins, and enzymes, some of which can be involved in virulence Nimrichter et al. A striking morphological phenomenon of C. This process has been studied in considerable depth in the yeast models S.
Biology and genetics of vegetative incompatibility in fungi
The difference relates to the mating cells of S. Following contact, the two partner cells fuse. However, when these diploid cells are starved of nutrients, they undergo meiosis to produce four-walled, haploid ascospores.
Whether C. Nevertheless, in this yeast there is clear evidence for a parasexual cycle whereby diploid cells mate to form tetraploid cells, which subsequently lose chromosomes in a random but concerted manner to return to the diploid state Nobile and Johnson Fungal spores are discrete cellular structures produced by virtually all fungi. Their form varies considerably and they can be unicellular or, as a result of septation, multicellular.
They can be derived either asexually, when they are collectively termed mitospores e. The types of spores and spore-producing structures, including multihyphal fruit bodies, are important features used in fungal classification, and the spore types produced by many fungal pathogens can assist in their identification see Chapter 2. All spores produced by human fungal pathogens are non-motile i.
The different types of fungal spores, along with their mechanisms of formation, modes of dispersal, and functions, have been recently reviewed Money These are the main mitospores produced by ascomycete pathogens e. Some pathogens e. Fusarium spp. Conidia are derived from specialized conidiogenous cells differentiated from hyphae. There are two basic types of conidium development: blastic and thallic conidiogenesis Webster and Weber ; Moore et al.
In blastic conidiogenesis , conidia are formed in a yeast bud-like manner from the tips or the sides of conidiogenous cells or from the spores at the ends of chains of conidia. In some fungi the conidiogenous cell is termed a phialide and is borne on a conidiophore stalk which is swollen at its apex to form a so-called vesicle Figure 4. Spores formed by this blastic mechanism are often referred to as blastospores. For instance, the budding yeast cells of C. The genetic control of blastic conidiogenesis, and its regulation by environmental factors particularly light , has been intensively studied in A.
Note the chains of conidia produced from bottle-shaped phialides conidiogenous cells borne on top of a conidiophore, which is swollen at its apex to form a vesicle. Image obtained by low-temperature scanning electron microscopy.
Reproduced with permission from Read N. In: Mendgen K. In thallic conidiogenesis , individual hyphal compartments of a pre-existing hypha differentiate into conidia, and this culminates in their physical separation by binary fission or hyphal fragmentation. Spores of this type are often referred to as arthrospores and are important infectious agents in pathogens such as Coccidioides and many dermatophytes. These are typically large, spherical, thick-walled, pigmented mitospores that are produced singly or in chains either at hyphal tips or in subapical hyphal regions.
They are produced by a wide range of human fungal pathogens, including C. These are mitospores produced by cytoplasmic cleavage coupled with cell wall synthesis within a multinucleate sporangium that is borne on a specialized hyphal stalk called a sporangiophore. They are the infectious agents of members of the Mucorales Webster and Weber ; Reiss et al.
Cellular and Molecular Biology of Filamentous Fungi
These are a unique type of fungal mitospore produced by the ascomycete pathogens Coccidioides immitis and C. The spherule develops from an inhaled arthroconidium that undergoes isotropic growth, and repeated nuclear divisions, followed by the progressive segmentation of the spherule protoplasm to form — walled, uninucleate endospores.
When spherules rupture, the endospores are released and are each capable of developing into a new spherule within the host Huppert et al.
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These are haploid meiospores produced externally from specialized cells derived from hyphae called basidia. Besides providing the spore with protection and morphology, spore cell walls also play other roles during infection. For example, in A. Spores released into the air rapidly dehydrate and thus have a low water content and no metabolic activity, and are therefore dormant.
Cellular and Molecular Biology of Filamentous Fungi - Google книги
This dormancy may be broken simply by the spore becoming rehydrated and exposed to favourable conditions for germination. In other cases, spores may impose a longer period of dormancy on themselves once they have arrived at a suitable site for germination. One common cause of this is when spores release a germination self-inhibitor that prevents germination at high spore concentrations as a way of reducing competition for nutrient resources Ugalde and Rodriguez-Urra Spores can germinate to produce specialized hyphae called germ tubes, involved in colony establishment Figure 4.
Some e. Prior to germination, spores commonly undergo a period of isotropic growth which, in some fungi e. Numerous changes in gene expression and biochemical changes occur during the germination process Kasuga et al. Spores can be uninucleate e. Marked avoidance responses negative tropisms are typically observed between germinating spores that are close to each other.
Initially, germ tubes emerge at sites on the spore surface that are as far as possible from the sites of germination on adjacent spores. The growing germ tubes also avoid adjacent germ tubes Figure 4. The chemical identity of the avoidance factor s released by spores, germ tubes, and vegetative hyphae has not yet been determined.
Note that germ tubes growing out from the aggregated conidia are exhibiting avoidance responses negative tropisms. Reproduced courtesy of Kathryn M. Lord and Nick D. Thanks are due to Drs Geoff Robson and Darren Thomson for helping me identify recent literature on the topic of this chapter, to Darren and Dr Kathryn Lord for providing unpublished images, and to Darren for assisting in the preparation of the figures.
Nature — Find this resource:. Fungal Genet Biol — Fungal Biol Rev 7— Nat Microbiol 52— Bartnicki-Garcia S, Hergert F and Gierz G Computer simulation of fungal morphogenesis and the mathematical basis for hyphal tip growth. Protoplasma 46— Infect Immun — Microbiol Spectra 3: doi MB Find this resource:. Nat Rev Microbiol 9: — Berman J Morphogenesis and cell cycle progression in Candida albicans.
Curr Opin Microbiol 9: — MBio 6: e— Mol Microbiol — Bioessays — Boyce K and Andrianopoulos A Morphogenetic circuitry regulating growth and development in the dimorphic pathogen Penicillium marneffei. Eukaryot Cell — Trends Genet — Current Opin Microbiol — Fischer R, Zekert N and Takeshita N Polarized growth in fungi—the interplay between the cytoskeleton, positional markers and membrane domains.
Gauthier GM Dimorphism in fungal pathogens of mammals, plants and insects. PLoS Pathog e Gladfelter A Nuclear anarchy: asynchronous mitosis in multinucleated fungal hyphae. Current Opin Microbiol 9: — Curr Microbiol 4: — Harris SD The duplication cycle of Aspergillus nidulans. Fungal Genet Biol 1— Harris SD Morphogenesis is coordinated with nuclear division in germinating Aspergillus nidulans conidiospores. Microbiology — Harris SD Branching of fungal hyphae: regulation, mechanisms and comparison with other branching systems.
Mycologia — Curr Opin Microbiol 53—9.
Med Mycol S— Higuchi Y and Steinberg G Early endosomes motility in filamentous fungi: how and why they move.
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