Spore formation is an essential step in the fungal life cycle that contributes to
the dispersal of the organism and also to survival under harsh environmental
conditions. The morphology of spores shows an astonishing diversity in the
fungal kingdom and varies from very simple round and small spores to very
complex multi-armed or sigmoid structures. With exception of the regulation of
ascospore formation in Saccharomyces cerevisiae and Schizosaccharomyces
pombe, which are well-characterized model organisms for spore development in
fungi, little is currently known about the regulation of more complex spore
morphologies.
In this study, the filamentous ascomycete Ashbya gossypii is used as a model
system for the investigation of a complex and composite spore morphology. A.
gossypii produces linear, needle-shaped spores possessing a length of 30 µm,
which can be divided into three major segments: a rigid tip segment, a more
fragile membrane compartment and a stable tail-cap. Furthermore, the different
compartments were shown to correlate with distinct materials. While the tip
segment and the tail-cap of the spores consist of stabilizing materials like chitin
and chitosan, these materials are absent from the compartment in the middle.
The actin cytoskeleton plays an essential role in several steps of spore
formation in A. gossypii. Different regions of actin accumulation were identified
that directly correlate with the developing spores. Especially the developing tip
segment is characterized by heavy-bundled linear actin structures. Furthermore,
proteins of the formin family, a class of actin organizing proteins, were identified
to be directly involved in spore formation in A. gossypii. The formin AgBnr2
fulfills an actin-related key function during spore development by linking actin to
the spindle pole body during sporulation. Downregulation of AgBNR2 leads to
severe sporulation defects, indicating a central function in spore development.
Moreover, AgBni1, another representative of the formin family, also has a
regulatory function in size determination of the typical needle-shaped spores of
A. gossypii. Using a modified yeast two-hybrid approach, four potential
activators of the formin AgBni1 were identified: the Rho-type GTPases
AgRho1a, AgRho1b, AgRho3 and AgRho4. The interaction of AgBni1 with the
two Rho1 GTPases plays an important role during spore development. In this
study, the Rho binding domain of AgBni1 was further examined to identify
amino acids that are essential for the interaction with the Rho-type GTPases.
Using random mutagenesis combined with a two-hybrid screen, the point
mutation S250P in the Rho binding domain of AgBni1 was identified to reduce
the interaction of the formin with the Rho1 GTPases. Integration of AgBni1 S250P
causes an increase in spore length, suggesting a direct effect of this signaling
pathway in spore length determination. An actin-regulating protein network that
includes the formin AgBni1, the Rho-type GTPases AgRho1a and AgRho1b and
the paxillin-like protein AgPxl1 was identified to be mainly involved in the
regulation of the spore length. Thereby, this network seems to be involved in
the arrangement of the different spore compartments via the actin cytoskeleton.
| Identifer | oai:union.ndltd.org:uni-osnabrueck.de/oai:repositorium.ub.uni-osnabrueck.de:urn:nbn:de:gbv:700-2012052110160 |
| Date | 21 May 2012 |
| Creators | Lickfeld, Manuela |
| Contributors | Prof. Dr. Jürgen Heinisch, Prof. Dr. Achim Paululat |
| Source Sets | Universität Osnabrück |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf, application/zip |
| Rights | Namensnennung-NichtKommerziell-KeineBearbeitung 3.0 Unported, http://creativecommons.org/licenses/by-nc-nd/3.0/ |
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