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Eukaryotic Cell, October 2006, p. 1635-1647, Vol. 5, No. 10
1535-9778/06/$08.00+0     doi:10.1128/EC.00210-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The SH3/PH Domain Protein AgBoi1/2 Collaborates with the Rho-Type GTPase AgRho3 To Prevent Nonpolar Growth at Hyphal Tips of Ashbya gossypii{triangledown}

Philipp Knechtle, Jürgen Wendland,{dagger} and Peter Philippsen*

Molecular Microbiology, Biozentrum der Universität Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland

Received 3 July 2006/ Accepted 21 August 2006

Unlike most other cells, hyphae of filamentous fungi permanently elongate and lack nonpolar growth phases. We identified AgBoi1/2p in the filamentous ascomycete Ashbya gossypii as a component required to prevent nonpolar growth at hyphal tips. Strains lacking AgBoi1/2p frequently show spherical enlargement at hyphal tips with concomitant depolarization of actin patches and loss of tip-located actin cables. These enlarged tips can repolarize and resume hyphal tip extension in the previous polarity axis. AgBoi1/2p permanently localizes to hyphal tips and transiently to sites of septation. Only the tip localization is important for sustained elongation of hyphae. In a yeast two-hybrid experiment, we identified the Rho-type GTPase AgRho3p as an interactor of AgBoi1/2p. AgRho3p is also required to prevent nonpolar growth at hyphal tips, and strains deleted for both AgBOI1/2 and AgRHO3 phenocopied the respective single-deletion strains, demonstrating that AgBoi1/2p and AgRho3p function in a common pathway. Monitoring the polarisome of growing hyphae using AgSpa2p fused to the green fluorescent protein as a marker, we found that polarisome disassembly precedes the onset of nonpolar growth in strains lacking AgBoi1/2p or AgRho3p. AgRho3p locked in its GTP-bound form interacts with the Rho-binding domain of the polarisome-associated formin AgBni1p, implying that AgRho3p has the capacity to directly activate formin-driven actin cable nucleation. We conclude that AgBoi1/2p and AgRho3p support polarisome-mediated actin cable formation at hyphal tips, thereby ensuring permanent polar tip growth.

* Corresponding author. Mailing address: Molecular Microbiology, Biozentrum der Universität Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland. Phone: 41-61-267-14-80. Fax: 41-61-267-14-81. E-mail: peter.philippsen{at}unibas.ch.

{triangledown} Published ahead of print on 1 September 2006.

{dagger} Present address: Carlsberg Laboratory, Yeast Biology, DK-2500, Valby, Copenhagen, Denmark.

Eukaryotic Cell, October 2006, p. 1635-1647, Vol. 5, No. 10
1535-9778/06/$08.00+0     doi:10.1128/EC.00210-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Kohli, M., Galati, V., Boudier, K., Roberson, R. W., Philippsen, P. (2008). Growth-speed-correlated localization of exocyst and polarisome components in growth zones of Ashbya gossypii hyphal tips. J. Cell Sci. 121: 3878-3889 [Abstract] [Full Text]  
  • Zheng, W., Chen, J., Liu, W., Zheng, S., Zhou, J., Lu, G., Wang, Z. (2007). A Rho3 Homolog Is Essential for Appressorium Development and Pathogenicity of Magnaporthe grisea. Eukaryot Cell 6: 2240-2250 [Abstract] [Full Text]  
  • Dunkler, A., Wendland, J. (2007). Candida albicans Rho-Type GTPase-Encoding Genes Required for Polarized Cell Growth and Cell Separation. Eukaryot Cell 6: 844-854 [Abstract] [Full Text]  


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