Septum formation is regulated by the RHO4‐specific exchange factors BUD3 and RGF3 and by the landmark protein BUD4 in <i>Neurospora crassa</i>

Justa-Schuch, Daniela; Heilig, Yvonne; Richthammer, Corinna; Seiler, Stephan

doi:10.1111/j.1365-2958.2010.07093.x

Cited by 60 publications

(100 citation statements)

References 74 publications

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“…Finally, our genetic and biochemical analyses clearly establish that AnBud3 serves as a GEF that promotes activation of Rho4. A similar relationship between Bud3 and Rho4 has recently been described for another filamentous ascomycete fungus, N. crassa ( Justa-Schuch et al 2010). In this case, Bud3 also acts as a GEF for Rho4, which in turn directs assembly of the CAR at septation sites (Rasmussen and Glass 2005).…”

Section: Discussionmentioning

confidence: 84%

Regulation of Septum Formation by the Bud3–Rho4 GTPase Module inAspergillus nidulans

Justa-Schuch

Seiler

et al. 2010

Genetics

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The ability of fungi to generate polarized cells with a variety of shapes likely reflects precise temporal and spatial control over the formation of polarity axes. The bud site selection system of Saccharomyces cerevisiae represents the best-understood example of such a morphogenetic regulatory system. However, the extent to which this system is conserved in the highly polarized filamentous fungi remains unknown. Here, we describe the functional characterization and localization of the Aspergillus nidulans homolog of the axial bud site marker Bud3. Our results show that AnBud3 is not required for polarized hyphal growth per se, but is involved in septum formation. In particular, our genetic and biochemical evidence implicates AnBud3 as a guanine nucleotide exchange factor for the GTPase Rho4. Additional results suggest that the AnBud3-Rho4 module acts downstream of the septation initiation network to mediate recruitment of the formin SepA to the site of contractile actin ring assembly. Our observations provide new insight into the signaling pathways that regulate septum formation in filamentous fungi.

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Section: Discussionmentioning

confidence: 84%

Regulation of Septum Formation by the Bud3–Rho4 GTPase Module inAspergillus nidulans

Justa-Schuch

Seiler

et al. 2010

Genetics

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“…AFUA_5G07430 is similar to the GEFs SpRgf3 (S. pombe Rgf3) and NcRGF3 (N. crassa RGF3) of S. pombe and N. crassa, respectively. SpRgf3 is a GEF of SpRho1 and controls ␤-(1,3)-D-glucan biosynthesis and cytokinesis (17,18,28), while NcRGF3 of the filamentous fungus N. crassa was shown to be a specific GEF of NcRHO4 and controls septum formation (29). In this study, we focused on analyzing Rom2.…”

Section: Resultsmentioning

confidence: 99%

“…In A. nidulans, A. nidulans Bud3 (AnBud3) is a GEF of AnRho4 and essential for septum formation (36), and in N. crassa, even two nonredundant GEFs of NcRHO4 were identified, NcBUD3 and NcRGF3 (29). NcRGF3 is the homologue of AFUA_5G07430 which has a domain structure similar to Rom2 but is currently uncharacterized in Aspergillus.…”

Section: Discussionmentioning

confidence: 99%

Role of the Guanine Nucleotide Exchange Factor Rom2 in Cell Wall Integrity Maintenance of Aspergillus fumigatus

et al. 2013

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Aspergillus fumigatus is a mold and the causal agent of invasive aspergillosis, a systemic disease with high lethality. Recently, we identified and functionally characterized three stress sensors implicated in the cell wall integrity (CWI) signaling of this pathogen, namely, Wsc1, Wsc3, and MidA. Here, we functionally characterize Rom2, a guanine nucleotide exchange factor with essential function for the cell wall integrity of A. fumigatus. A conditional rom2 mutant has severe growth defects under repressive conditions and incorporates all phenotypes of the three cell wall integrity sensor mutants, e.g., the echinocandin sensitivity of the ⌬wsc1 mutant and the Congo red, calcofluor white, and heat sensitivity of the ⌬midA mutant. Rom2 interacts with Rho1 and shows a similar intracellular distribution focused at the hyphal tips. Our results place Rom2 between the cell surface stress sensors Wsc1, Wsc3, MidA, and Rho1 and their downstream effector mitogen-activated protein (MAP) kinase module Bck1-Mkk2-MpkA.

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“…Rasmussen and Glass further showed that RHO-4 localizes to septa and identified a difference in the regulation of septation during conidiation versus vegetative septation in N. crassa (44,45). Recent studies in N. crassa and A. nidulans indicate that RHO-4 localizes to septa and to the plasma membrane and is involved in signaling pathways that regulate septum formation (19,58).…”

Section: Discussionmentioning

confidence: 99%

A Mutant Defective in Sexual Development Produces Aseptate Ascogonia

et al. 2010

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The transition from the vegetative to the sexual cycle in filamentous ascomycetes is initiated with the formation of ascogonia. Here, we describe a novel type of sterile mutant from Sordaria macrospora with a defect in ascogonial septum formation. This mutant, named pro22, produces only small, defective protoperithecia and carries a point mutation in a gene encoding a protein that is highly conserved throughout eukaryotes. Sequence analyses revealed three putative transmembrane domains and a C-terminal domain of unknown function. Live-cell imaging showed that PRO22 is predominantly localized in the dynamic tubular and vesicular vacuolar network of the peripheral colony region close to growing hyphal tips and in ascogonia; it is absent from the large spherical vacuoles in the vegetative hyphae of the subperipheral region of the colony. This points to a specific role of PRO22 in the tubular and vesicular vacuolar network, and the loss of intercalary septation in ascogonia suggests that PRO22 functions during the initiation of sexual development.The formation of fruiting bodies in filamentous ascomycetes is a process of multicellular differentiation controlled by many developmentally regulated genes. The self-fertile ascomycete Sordaria macrospora represents an excellent model for studying cell differentiation during fungal fruiting body development (reviewed in references 9 and 24).During the life cycle of S. macrospora, a mature haploid ascospore germinates and produces a mycelium composed of multinucleate hyphal compartments. After 2 to 3 days, coiled female reproductive hyphae, called ascogonia, are formed. Each ascogonium develops further into a more-or-less spherical protoperithecium composed of pseudoparenchymatous tissue surrounding the original ascogonium (24, 47). Ascogenous hyphae emerge from the ascogonium inside the protoperithecium. Within the ascogenous hyphae, the nuclei pair up to form the dikaryotic state, even though S. macrospora is selffertile and does not require fertilization with an opposite mating type (11,49). The transition from the spherical protoperithecial to the flask-shaped perithecial stage, is believed to be stimulated by the formation of the dikaryon, although this has not been experimentally verified (24). The dikaryotic state in individual hyphal compartments of the growing ascogenous hyphae is maintained by precisely orchestrated crozier formation from the tip of an ascogenous hypha, fusion of the crozier tip with the penultimate cell of the ascogenous hypha, conjugate mitotic divisions, and highly regulated septation (50, 69). Karyogamy of two nuclei in the penultimate cell results in the formation of a diploid ascus mother cell. The diploid state is very short-lived because the diploid nuclei which are formed immediately undergo meiosis, followed by an extra mitotic division resulting in an ascus containing eight haploid ascospores (11,49). An identical process has been observed in the heterothallic fungus Neurospora crassa, with the exception that cell fusion between opposit...

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Septum formation is regulated by the RHO4‐specific exchange factors BUD3 and RGF3 and by the landmark protein BUD4 in Neurospora crassa

Cited by 60 publications

References 74 publications

Regulation of Septum Formation by the Bud3–Rho4 GTPase Module inAspergillus nidulans

Regulation of Septum Formation by the Bud3–Rho4 GTPase Module inAspergillus nidulans

Role of the Guanine Nucleotide Exchange Factor Rom2 in Cell Wall Integrity Maintenance of Aspergillus fumigatus

A Mutant Defective in Sexual Development Produces Aseptate Ascogonia

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