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Eukaryotic Cell, January 2009, p. 104-115, Vol. 8, No. 1
1535-9778/09/$08.00+0     doi:10.1128/EC.00265-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transcriptional Profiling Identifies a Role for BrlA in the Response to Nitrogen Depletion and for StuA in the Regulation of Secondary Metabolite Clusters in Aspergillus fumigatus{triangledown} ,{ddagger}

Kwame Twumasi-Boateng,1,{dagger} Yan Yu,2 Dan Chen,2 Fabrice N. Gravelat,1 William C. Nierman,2 and Donald C. Sheppard1*

Department of Microbiology and Immunology, McGill University, Montreal, Quebec H3A 2B4, Canada,1 J. Craig Venter Institute, Rockville, Maryland 208502

Received 5 August 2008/ Accepted 13 November 2008

Conidiation (asexual sporulation) is a key developmental process in filamentous fungi. We examined the gene regulatory roles of the Aspergillus fumigatus developmental transcription factors StuAp and BrlAp during conidiation. Conidiation was completely abrogated in an A. fumigatus {Delta}brlA mutant and was severely impaired in a {Delta}stuA mutant. We determined the full genome conidiation transcriptomes of wild-type and {Delta}brlA and {Delta}stuA mutant A. fumigatus and found that BrlAp and StuAp governed overlapping but distinct transcriptional programs. Six secondary metabolite biosynthetic clusters were found to be regulated by StuAp, while only one cluster exhibited BrlAp-dependent expression. The {Delta}brlA mutant, but not the {Delta}stuA mutant, had impaired downregulation of genes encoding ribosomal proteins under nitrogen-limiting, but not carbon-limiting, conditions. Interestingly, inhibition of the target of rapamycin (TOR) pathway also caused downregulation of ribosomal protein genes in both the wild-type strain and the {Delta}brlA mutant. Downregulation of these genes by TOR inhibition was associated with conidiation in the wild-type strain but not in the {Delta}brlA mutant. Therefore, BrlAp-mediated repression of ribosomal protein gene expression is not downstream of the TOR pathway. Furthermore, inhibition of ribosomal protein gene expression is not sufficient to induce conidiation in the absence of BrlAp.

* Corresponding author. Mailing address: Lyman Duff Medical Building, 3775 University St., Rm. 502, Montreal, Quebec H3A 2B4, Canada. Phone: (514) 398-1759. Fax: (514) 398-7052. E-mail: don.sheppard{at}mcgill.ca

{triangledown} Published ahead of print on 21 November 2008.

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

{dagger} Present address: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102.

Eukaryotic Cell, January 2009, p. 104-115, Vol. 8, No. 1
1535-9778/09/$08.00+0     doi:10.1128/EC.00265-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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