Selective activation by the guanine nucleotide exchange factor Don1 is a main determinant of Cdc42 signalling specificity in <i>Ustilago maydis</i>

Hlubek, Andrea; Schink, Kay Oliver; Mahlert, Michael; Sandrock, Björn; Bölker, Michael

doi:10.1111/j.1365-2958.2008.06177.x

Cited by 21 publications

(25 citation statements)

References 39 publications

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“…The change of fluorescence over time was used to assess mant-GDP incorporation into Rho4 in the presence and absence of the GEF. Similar conditions were also used in recent publications by Yeh et al (2007) and Hlubek et al (2008). The latter authors also used equal amounts of GEF and GTPase.…”

Section: Genetic Interaction Experimentsmentioning

confidence: 91%

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: Genetic Interaction Experimentsmentioning

confidence: 91%

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

Justa-Schuch

Seiler

et al. 2010

Genetics

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“…In addition, overexpression of Rho1 led to the reduction of filamentation. Overexpression of Rac1 triggers filamentation in U. maydis (13,29). We show here that deleting Rac1 eliminates the lethal effect imposed by either Rho1 or Pdc1 depletion.…”

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confidence: 83%

Ustilago maydis Rho1 and 14-3-3 Homologues Participate in Pathways Controlling Cell Separation and Cell Polarity

Pham

Sandrock

et al. 2009

Eukaryot Cell

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Proteins of the 14-3-3 and Rho-GTPase families are functionally conserved eukaryotic proteins that participate in many important cellular processes such as signal transduction, cell cycle regulation, malignant transformation, stress response, and apoptosis. However, the exact role(s) of these proteins in these processes is not entirely understood. Using the fungal maize pathogen, Ustilago maydis, we were able to demonstrate a functional connection between Pdc1 and Rho1, the U. maydis homologues of 14-3-3 and Rho1, respectively. Our experiments suggest that Pdc1 regulates viability, cytokinesis, chromosome condensation, and vacuole formation. Similarly, U. maydis Rho1 is also involved in these three essential processes and exerts an additional function during mating and filamentation. Intriguingly, yeast two-hybrid and epistasis experiments suggest that both Pdc1 and Rho1 could be constituents of the same regulatory cascade(s) controlling cell growth and filamentation in U. maydis. Overexpression of rho1 ameliorated the defects of cells depleted for Pdc1. Furthermore, we found that another small G protein, Rac1, was a suppressor of lethality for both Pdc1 and Rho1. In addition, deletion of cla4, encoding a Rac1 effector kinase, could also rescue cells with Pdc1 depleted. Inferring from these data, we propose a model for Rho1 and Pdc1 functions in U. maydis.Morphological switching is a unique attribute of all dimorphic fungi, which alternate between budding and filamentous growth. In some cases, as with mating, this is a prerequisite for genetic diversity for this subfamily of fungi. In addition, many dimorphic fungal pathogens rely on this ability in order to effectively invade their host. In general, the transition between these alternate life forms means a complete turnover of cellular and proteomic components, which often involves cell cycle arrest and/or cytoskeletal rearrangement. Although the cellular proteomes associated with these two processes share many components, there are both temporal and spatial regulations that are manifested during the transitional phase (4).Temporal-spatial regulation of the proteome during the dimorphic transition requires cooperation and synchronized communication among different regulatory pathways. Two highly intricate, yet well-established, signaling cascades that regulate fungal morphogenesis are the mitogen-activated protein kinase (MAPK) (34, 46) and protein kinase A pathways (11). These signaling cascades detect and perpetuate extracellular stimuli, e.g., pheromones and nutrients, which lead to phase transitions in dimorphic fungi. Although the mechanisms are not as fully understood, members of two highly conserved families of proteins, Rho/Rac GTPases and 14-3-3 proteins, have also been shown to control filamentation. Constituents of the Rho/Rac protein family have been shown to regulate actin organization (26,35,36), cytokinesis (3, 49, 52), cell integrity (42, 56), pathogenicity (29), signal transduction (22,44,56), and cell migration (8). Their activity is dependent...

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“…Cdc42, the yeast homolog of RacA, is a substrate of Cdc24 (24). In U. maydis, Don1 was identified as the GEF for Cdc42, and Cdc24 is proposed as the GEF for RacA to control the processes of cell septation and polarized growth, respectively (18,25,26). We previously showed that interaction of the GTP bound form of RacA with NoxR is essential for activation of the fungal Nox (13,16).…”

Section: Discussionmentioning

confidence: 99%

Polarity proteins Bem1 and Cdc24 are components of the filamentous fungal NADPH oxidase complex

Takemoto

Kamakura

Saikia

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

124

140

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Regulated synthesis of reactive oxygen species (ROS) by membrane-bound fungal NADPH oxidases (Nox) plays a key role in fungal morphogenesis, growth, and development. Generation of reactive oxygen species (ROS) by the plant symbiotic fungus, Epichloë festucae , requires functional assembly of a multisubunit complex composed of NoxA, a regulatory component, NoxR, and the small GTPase RacA. However, the mechanism for assembly and activation of this complex at the plasma membrane is unknown. We found by yeast two-hybrid and coimmunoprecipitation assays that E. festucae NoxR interacts with homologs of the yeast polarity proteins, Bem1 and Cdc24, and that the Phox and Bem1 (PB1) protein domains found in these proteins are essential for these interactions. GFP fusions of BemA, Cdc24, and NoxR preferentially localized to actively growing hyphal tips and to septa. These proteins interact with each other in vivo at these same cellular sites as shown by bimolecular fluorescent complementation assays. The PB1 domain of NoxR is essential for localization to the hyphal tip. An E. festucae Δ bemA mutant was defective in hyphal morphogenesis and growth in culture and in planta . The changes in fungal growth in planta resulted in a defective symbiotic interaction phenotype. Our inability to isolate a Δ cdc24 mutant suggests this gene is essential. These results demonstrate that BemA and Cdc24 play a critical role in localizing NoxR protein to sites of fungal hyphal morphogenesis and growth. Our findings identify a potential shared ancestral link between the protein machinery required for fungal polarity establishment and the Nox complex controlling cellular differentiation.

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Selective activation by the guanine nucleotide exchange factor Don1 is a main determinant of Cdc42 signalling specificity in Ustilago maydis

Cited by 21 publications

References 39 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

Ustilago maydis Rho1 and 14-3-3 Homologues Participate in Pathways Controlling Cell Separation and Cell Polarity

Polarity proteins Bem1 and Cdc24 are components of the filamentous fungal NADPH oxidase complex

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