Originally published as Genetics Published Articles Ahead of Print on April 19, 2006.
Genetics, Vol. 173, 685-696, June 2006, Copyright © 2006
doi:10.1534/genetics.105.054304
Isolation of Mutations That Bypass the Requirement of the Septation Initiation Network for Septum Formation and Conidiation in Aspergillus nidulans
Jung-Mi Kim,
Ling Lu,
Rongzhong Shao,
Jaclyn Chin and
Bo Liu1
Section of Plant Biology, University of California, Davis, California 95616
1 Corresponding author: Section of Plant Biology, University of California, 1 Shields Avenue, 1002 Life Sciences Addition, Davis, CA 95616-8537.
E-mail: bliu{at}ucdavis.edu
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. 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.
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Copyright © 2006 by the Genetics Society of America.