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Targeted Gene Silencing in the Model Mushroom Coprinopsis cinerea (Coprinus cinereus) by Expression of Homologous Hairpin RNAs

Martin A. Wälti, Cristina Villalba, Reto M. Buser, Anke Grünler, Markus Aebi, and Markus Künzler^*

Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland

Received 16 September 2005/ Accepted 19 January 2006

The ink cap Coprinopsis cinerea is a model organism for studying fruiting body (mushroom) formation in homobasidiomycetes. Mutant screens and expression studies have implicated a number of genes in this developmental process. Functional analysis of these genes, however, is hampered by the lack of reliable reverse genetics tools for C. cinerea. Here, we report the applicability of gene targeting by RNA silencing for this organism. Efficient silencing of both an introduced GFP expression cassette and the endogenous cgl1 and cgl2 isogenes was achieved by expression of homologous hairpin RNAs. In latter case, silencing was the result of a hairpin construct containing solely cgl2 sequences, demonstrating the possibility of simultaneous silencing of whole gene families by a single construct. Expression of the hairpin RNAs reduced the mRNA levels of the target genes by at least 90%, as determined by quantitative real-time PCR. The reduced mRNA levels were accompanied by cytosine methylation of transcribed and nontranscribed DNA at both silencing and target loci in the case of constitutive high-level expression of the hairpin RNA but not in the case of transient expression. These results suggest the presence of both posttranscriptional and transcriptional gene silencing mechanisms in C. cinerea and demonstrate the applicability of targeted gene silencing as a powerful reverse genetics approach in this organism.

Present address: Institute of Molecular Biology and Biophysics, ETH Zürich, Schafmattstr. 20, CH-8093 Zürich, Switzerland.