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Eukaryotic Cell, August 2007, p. 1497-1510, Vol. 6, No. 8
1535-9778/07/$08.00+0     doi:10.1128/EC.00281-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

MpkA-Dependent and -Independent Cell Wall Integrity Signaling in Aspergillus nidulans ^,

Laboratory of Enzymology, Department of Molecular and Cell Biology, Graduate School of Agricultural Science, Tohoku University, 1-1 Amamiya, Tsutsumi-dori, Sendai 981-8555,¹ New Industry Creation Hatchery Center, ABE Project, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan²

Received 3 September 2006/ Accepted 11 June 2007

Cell wall integrity signaling (CWIS) maintains cell wall biogenesis in fungi, but only a few transcription factors (TFs) and target genes downstream of the CWIS cascade in filamentous fungi are known. Because a mitogen-activated protein kinase (MpkA) is a key CWIS enzyme, the transcriptional regulation of mpkA and of cell wall-related genes (CWGs) is important in cell wall biogenesis. We cloned Aspergillus nidulans mpkA; rlmA, a TF gene orthologous to Saccharomyces cerevisiae RLM1 that encodes Rlm1p, a major Mpk1p-dependent TF that regulates the transcription of MPK1 besides that of CWGs; and Answi4 and Answi6, homologous to S. cerevisiae SWI4 and SWI6, encoding the Mpk1p-activating TF complex Swi4p-Swi6p, which regulates CWG transcription in a cell cycle-dependent manner. A. nidulans rlmA and mpkA cDNA functionally complemented S. cerevisiae rlm1 and mpk1 mutants, respectively, but Answi4 and Answi6 cDNA did not complement swi4 and swi6 mutants. We constructed A. nidulans rlmA, Answi4 and Answi6, and mpkA disruptants (rlmA, Answi4 Answi6, and mpkA strains) and analyzed mpkA and CWG transcripts after treatment with a ß-1,3-glucan synthase inhibitor (micafungin) that could activate MpkA via CWIS. Levels of mpkA transcripts in the mutants as well as those in the wild type were changed after micafungin treatment. The ß-glucuronidase reporter gene controlled by the mpkA promoter was expressed in the wild type but not in the mpkA strain. Thus, mpkA transcription seems to be autoregulated by CWIS via MpkA but not by RlmA or AnSwi4-AnSwi6. The transcription of most CWGs except -1,3-glucan synthase genes (agsA and agsB) was independent of RlmA and AnSwi4-AnSwi6 and seemed to be regulated by non-MpkA signaling. The transcriptional regulation of mpkA and of CWGs via CWIS in A. nidulans differs significantly from that in S. cerevisiae.

Published ahead of print on 29 June 2007.

Supplemental material for this article may be found at http://ec.asm.org/.

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