title: The post-transcriptional gene silencing machinery functions independently of DNA methylation to repress a LINE1-like retrotransposon in Neurospora crassa.
abstract: Post-transcriptional gene silencing (PTGS) involving small interfering RNA (siRNA)-directed degradation of RNA transcripts and transcriptional silencing via DNA methylation have each been proposed as mechanisms of genome defence against invading nucleic acids, such as transposons and viruses. Furthermore, recent data from plants indicates that many transposons are silenced via a combination of the two mechanisms, and siRNAs can direct methylation of transposon sequences. We investigated the contribution of DNA methylation and the PTGS pathway to transposon control in the filamentous fungus Neurospora crassa. We found that repression of the LINE1-like transposon, Tad, requires the Argonaute protein QDE2 and Dicer, each of which are required for transgene-induced PTGS (quelling) in N.crassa. Interestingly, unlike quelling, the RNA-dependent RNA polymerase QDE1 and the RecQ DNA helicase QDE3 were not required for Tad control, suggesting the existence of specialized silencing pathways for diverse kinds of repetitive elements. In contrast, Tad elements were not significantly methylated and the DIM2 DNA methyltransferase, responsible for all known DNA methylation in Neurospora, had no effect on Tad control. Thus, an RNAi-related transposon silencing mechanism operates during the vegetative phase of N.crassa that is independent of DNA methylation, highlighting a major difference between this organism and other methylation-proficient species.
authors.affiliation: Dipartimento di Biotecnologie Cellulari ed Ematologia, Sezione di Genetica Molecolare, Universita' di Roma La Sapienza 00161 Rome, Italy.
authors.forename: Tony
authors.initials: T
authors.lastname: Nolan
authors.forename: Laura
authors.initials: L
authors.lastname: Braccini
authors.forename: Gianluca
authors.initials: G
authors.lastname: Azzalin
authors.forename: Arianna
authors.initials: A
authors.lastname: De Toni
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Macino
authors.forename: Carlo
authors.initials: C
authors.lastname: Cogoni
mesh_terms: D019175:DNA Methylation; D015966:Gene Expression Regulation, Fungal; D020084:Long Interspersed Nucleotide Elements; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000096:biosynthesis; D043244:Ribonuclease III / Q000235:genetics
chemical_list: D034741:RNA, Small Interfering; D043244:Ribonuclease III