Probable RNA helicase required for post-transcriptional gene silencing (PTGS), a process that provides protection in plants against virus infection and can suppress expression of transgenes. Plays a central role in RNA interference (RNAi) process, a process that mediates mRNA destruction of translational repression. Required for the assembly of the RISC complex, a complex required for target RNA destruction or repression. May be required in the RISC assembly to unwind miRNAs, in the production of single-stranded miRNA from the double-stranded miRNA, a key step in RISC formation. Involved in the amplification of sense-PTGS (S-PTGS), leading to siRNA production. Required for the maintenance but not the initiation of tobacco rattle virus (TRV)-mediated silencing, probably by mediating/maintaining DNA methylation and chromatin-based transcriptional gene silencing at some genomic locations. ATP + H2O = ADP + H(+) + phosphate Interacts with AGO1 and AGO2. Delayed loss of transgene silencing (post-transcriptional gene silencing (PTGS)), with full silencing in the cotyledons and in the hypocotyl, contrasting with a loss of silencing in true leaves. Impaired maintenance of tobacco rattle virus (TRV)-mediated silencing. Reduced methylation of cytosine residues in targets loci but enrichment of histone-H3 'Lys-4' methylation (H3K4me3) at the same sites. Belongs to the DNA2/NAM7 helicase family. SDE3 subfamily.