The RNA-dependent RNA polymerase, QDE-1, is a rate-limiting factor in post-transcriptional gene silencing in Neurospora crassa

The RNA-dependent RNA polymerase (RdRP) qde-1 is an essential component of post-transcriptional gene silencing (PTGS), termed 'quelling' in the fungus Neurospora crassa. Here we show that the overexpression of QDE-1 results in a dramatic increase in the efficiency of quelling, with a concomitant net increase in the quantity of al-1 siRNAs. Moreover, in overexpressed strains there is a significant reduction in the number of transgenes required to induce quelling, and an increase in the phenotypic stability despite progressive loss of tandemly repeated transgenes, which normally determines reversion of a silenced phenotype to wild type. These data suggest that the activation and maintenance of silencing in Neurospora appear to rely both on the cellular amount of QDE-1 and the amount of transgenic copies producing RNA molecules that act as a substrate for the RdRP, implicating QDE-1 as a rate-limiting factor in PTGS.