Ras1-induced hyphal development in Candida albicans requires the formin Bni1.
Formins are downstream effector proteins of Rho-type GTPases and are involved in the organization of the actin cytoskeleton and actin cable assembly at sites of polarized cell growth. Here we show using in vivo time-lapse microscopy that deletion of the Candida albicans formin homolog BNI1 results in polarity defects during yeast growth and hyphal stages. Deletion of the second C. albicans formin, BNR1, resulted in elongated yeast cells with cell separation defects but did not interfere with the ability of bnr1 cells to initiate and maintain polarized hyphal growth. Yeast bni1 cells were swollen, showed an increased random budding pattern, and had a severe defect in cytokinesis, with enlarged bud necks. Induction of hyphal development in bni1 cells resulted in germ tube formation but was halted at the step of polarity maintenance. Bni1-green fluorescent protein is found persistently at the hyphal tip and colocalizes with a structure resembling the Spitzenkörper of true filamentous fungi. Introduction of constitutively active ras1G13V in the bni1 strain or addition of cyclic AMP to the growth medium did not bypass bni1 hyphal growth defects. Similarly, these agents were not able to suppress hyphal growth defects in the wal1 mutant which is lacking the Wiskott-Aldrich syndrome protein (WASP) homolog. These results suggest that the maintenance of polarized hyphal growth in C. albicans requires coordinated regulation of two actin cytoskeletal pathways, including formin-mediated secretion and WASP-dependent endocytosis.
Martin
Ronny
R
Junior Research Group: Growth Control of Fungal Pathogens, Leibniz Institute for Natural Products Research and Infection Biology, Friedrich-Schiller-University, Beutenbergstr. 11a, D-07745 Jena, Germany.
Walther
Andrea
A
Wendland
Jürgen
J
D000199:Actins / Q000378:metabolism; D002176:Candida albicans / Q000166:cytology / Q000502:physiology; D016764:Cell Polarity; D000242:Cyclic AMP / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004705:Endocytosis; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D025301:Hyphae / Q000378:metabolism* / Q000648:ultrastructure; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D000199:Actins; C105191:Bni1 protein, S cerevisiae; D005656:Fungal Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D000242:Cyclic AMP; D018631:ras Proteins