Involved in RNA-mediated post-transcriptional gene silencing (PTGS). Main component of the RNA-induced silencing complex (RISC) that binds to a short guide RNA such as a microRNA (miRNA) or small interfering RNA (siRNA). RISC uses the mature miRNA or siRNA as a guide for slicer-directed cleavage of homologous mRNAs to repress gene expression. Required for the processing of 21 nucleotide trans-acting siRNAs (ta-siRNAs) derived from TAS3a transcripts. Associates preferentially with the microRNA (miRNA) miR390 which guides the cleavage of TAS3 precursor RNA. Seems to act as miR390 specific slicer. Associates mainly with small RNAs of 21 nucleotide in length and with a 5' terminal adenosine. Acts in the RDR6/SGS3/DCL4/AGO7 trans-acting siRNA pathway involved in leaf developmental timing. Does not seems to act on leaf polarity. Required for the production of the 30-40nt bacterial-induced long siRNAs (lsiRNA). Involved in antiviral RNA silencing by contributing to efficient viral RNAs clearance. Targets less structured viral RNAs than AGO1 which is capable of targeting RNAs with more compact structures. Expressed in leaves and floral buds, and at low levels in roots. First leaves are elongated and curl downward. Increased number of hydathodes per leaf. Accelerated appearance of abaxial trichomes. Presence of stigmatic tissue in the middle of the septum at the apical end of the carpels. Belongs to the argonaute family. Ago subfamily.