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Eukaryotic Cell, December 2005, p. 2029-2043, Vol. 4, No. 12
1535-9778/05/$08.00+0 doi:10.1128/EC.4.12.2029-2043.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Kylie J. Boyce,1
Austin So,1
Barbara R. Steen,1,
Steven Jones,2
Marco Marra,2 and
James W. Kronstad1*
Michael Smith Laboratories, Department of Microbiology and Immunology, and Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC V6T 1Z4, Canada,1 Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, BC V5Z 4S6, Canada2
Received 11 August 2005/ Accepted 8 September 2005
The switch from budding to filamentous growth is a key aspect of invasive growth and virulence for the fungal phytopathogen Ustilago maydis. The cyclic AMP (cAMP) signaling pathway regulates dimorphism in U. maydis, as demonstrated by the phenotypes of mutants with defects in protein kinase A (PKA). Specifically, a mutant lacking the regulatory subunit of PKA encoded by the ubc1 gene displays a multiple-budded phenotype and fails to incite disease symptoms, although proliferation does occur in the plant host. A mutant with a defect in a catalytic subunit of PKA, encoded by adr1, has a constitutively filamentous phenotype and is nonpathogenic. We employed serial analysis of gene expression to examine the transcriptomes of a wild-type strain and the ubc1 and adr1 mutants to further define the role of PKA in U. maydis. The mutants displayed changes in the transcript levels for genes encoding ribosomal proteins, genes regulated by the b mating-type proteins, and genes for metabolic functions. Importantly, the ubc1 mutant displayed elevated transcript levels for genes involved in phosphate acquisition and storage, thus revealing a connection between cAMP and phosphate metabolism. Further experimentation indicated a phosphate storage defect and elevated acid phosphatase activity for the ubc1 mutant. Elevated phosphate levels in culture media also enhanced the filamentous growth of wild-type cells in response to lipids, a finding consistent with PKA regulation of morphogenesis in U. maydis. Overall, these findings extend our understanding of cAMP signaling in U. maydis and reveal a link between phosphate metabolism and morphogenesis.
Present address: Department of Genetics, E.T.S.I.A., Universidad Politécnica de Madrid, E-28040 Madrid, Spain.
Present address: Response Biomedical Corporation, 8081 Lougheed Highway, Burnaby, BC V5A 1W9, Canada.
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