Genetics. Published Articles Ahead of Print: April 19, 2006, Copyright © 2006
doi:10.1534/genetics.105.054304


A more recent version of this article appeared on June 1, 2006.


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Isolation of mutations that bypass the requirement of the septation initiation network for septum formation and conidiation in Aspergillus nidulans

1 University of California

* To whom correspondence should be addressed. E-mail: bliu{at}ucdavis.edu.

Submitted on December 5, 2005
Revised on December 23, 2005
Accepted on 7 April 2006


Abstract

The kinase cascade of the septation initiation network (SIN), first revealed in fission yeast, activates the contraction of the actomyosin ring, and plays an essential role in fungal septation. Mob1p, an evolutionarily conserved SIN protein, is associated with the most downstream kinase of this cascade in fission yeast. In this study, the mobA gene encoding a homologous protein was isolated from the filamentous fungus Aspergillus nidulans, whose mycelium is made of multinucleate cells. The MOBA protein was required for septation and conidiation, but was not essential for hyphal extension and colony formation. In order to identify genes that act antagonistically against the SIN, UV mutagenesis was carried out to isolate suppressor (smo) mutations that restored conidiation when MOBA was not expressed. Microscopic examination indicated that the restored conidiation was concomitant with restored septation in the absence of the MOBA protein. Eight recessive smo mutations in five complementation groups also bypassed the requirement of the SIN kinases SEPH and SIDB for septum formation and conidiation. However, none of these smo mutations affected the localization of MOBA. Among smo mutations, smoA and smoB mutations caused reduced hyphal growth and colony formation. They also rendered hypersensitivity to low doses of the microtubule-depolymerizing agent benomyl for conidiation. Therefore, in A. nidulans, proteins encoded by the smo genes likely have an antagonistic interaction against the SIN pathway to regulate septation and conidiation.

Key Words: Aspergillus nidulans, cytokinesis/septation, mob1, septation initiation network (SIN), spindle pole body




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