The PHOA and PHOB Cyclin-Dependent Kinases Perform an Essential Function in Aspergillus nidulans

The PHOA and PHOB Cyclin-Dependent Kinases Perform an Essential Function in Aspergillus nidulans

Xiaowei Dou^a, Dongliang Wu^a, Weiling An^a, Jonathan Davies^a, Shahr B. Hashmi^a, Leena Ukil^a, and Stephen A. Osmani^a
^a Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43210

Corresponding author: Stephen A. Osmani, The Ohio State University, 804 Riffe Bldg., 496 W. 12th Ave., Columbus, OH 43210. E-mail osmani.2@osu.edu

Communicating editor: B. ANDREWS

Unlike Pho85 of Saccharomyces cerevisiae, the highly relatedPHOA cyclin-dependent kinase (CDK) of Aspergillus nidulans playsno role in regulation of enzymes involved in phosphorous acquisitionbut instead modulates differentiation in response to environmentalconditions, including limited phosphorous. Like PHO85, AspergillusphoA is a nonessential gene. However, we find that expressionof dominant-negative PHOA inhibits growth, suggesting it mayhave an essential but redundant function. Supporting this wehave identified another cyclin-dependent kinase, PHOB, whichis 77% identical to PHOA. Deletion of phoB causes no phenotype,even under phosphorous-limited growth conditions. To investigatethe function of phoA/phoB, double mutants were selected froma cross of strains containing null alleles and by generatinga temperature-sensitive allele of phoA in a ${Delta}$ phoB background.Double-deleted ascospores were able to germinate but had a limitedcapacity for nuclear division, suggesting a cell cycle defect.Longer germination revealed morphological defects. The temperature-sensitivephoA allele caused both nuclear division and polarity defectsat restrictive temperature, which could be complemented by expressionof mammalian CDK5. Therefore, an essential function exists inA. nidulans for the Pho85-like kinase pair PHOA and PHOB, whichmay involve cell cycle control and morphogenesis.

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