The RNAi Machinery in the Fungus Is Not Very Active in Synthetic Medium and Is Related to Transposable Elements.

Small RNAS (sRNAs) participate in regulatory RNA interference (RNAi) mechanisms in a wide range of eukaryotic organisms, including fungi. The fungus , a model for the study of secondary metabolism, contains a complete set of genes for RNAi pathways. We have analyzed by high-throughput sequencing the content of sRNAs in total RNA samples of grown in synthetic medium in the dark or after 1 h of illumination, using libraries below 150 nt, covering sRNAs and their precursors. For comparison, a parallel analysis with was carried out. The sRNA reads showed a higher proportion of 5' uracil in the RNA samples of the expected sizes in both species, indicating the occurrence of genuine sRNAs, and putative miRNA-like sRNAs (milRNAS) were identified with prediction software. carries at least one transcriptionally expressed Ty1/copia-like retrotransposable element, in which sRNAs were found in both sense and antisense DNA strands, while in skippy-like elements also show sRNA formation. The finding of sRNA in these mobile elements indicates an active sRNA-based RNAi pathway. Targeted deletion of , the only Dicer gene with significant expression under the conditions tested, did not produce appreciable phenotypic or transcriptomic alterations.