RNA silencing gene truncation in the filamentous fungus Aspergillus nidulans

Department of Plant Pathology, University of Wisconsin, Madison, WI, 53706; Institut de Génétique et Microbiologie, Université Paris-Sud, UMR 8621 CNRS, Paris, France; Dept. of Microbiology, Imperial College London, London, UK

^* To whom correspondence should be addressed. Email: npk{at}plantpath.wisc.edu.

	Abstract

The genus Aspergillus is ideally suited towards the investigation of RNA silencing evolution because it includes species that have experienced a variety of RNA silencing gene changes. Our work on this subject begins here with the model species Aspergillus nidulans. Filamentous ascomycete fungi generally each encode two of the core RNA silencing proteins, Dicer and Argonaute, but A. nidulans appears to have lost one of each to gene-truncation events. Although a role in growth, development or RNA silencing was not detected for the truncated genes, they do produce spliced and poly-A tailed transcripts, suggesting that they may have an undetermined biological function. Population analysis demonstrates that the truncated genes are fixed at the species level and that their full-length orthologs in a closely related species are also unstable. With these gene truncation events, A. nidulans encodes only a single intact Dicer and Argonaute. Their deletion results in morphologically- and reproductively-normal strains that are incapable of experimental RNA silencing. Thus our results suggest that the remaining A. nidulans RNA silencing genes have a non-"housekeeping" function, such as defense against viruses and transposons.