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 reliable formation of primary and axillary shoot apical meristems. Specifies leaf adaxial identity by repressing the miR165 and miR166 microRNAs in the embryonic shoot apex, in the shoot apical meristem (SAM) and leaf. Represses the microRNA miR398 which targets CCS1 chaperone mRNAs for translational inhibition. Acts as a negative regulator of AGO1 protein level. Like AGO1, is required for stem cell function and organ polarity. Unlike AGO1, is not subjected to small RNA-mediated repression itself. Essential for multiple processes in development. Coregulates, with GATA18/HAN, the shoot apical meristem (SAM) organization (PubMed:26390296). Interacts with GATA18/HAN and KNAT1/BP (PubMed:26390296). Interacts with RICE1 and RICE2 that act as cofactors (PubMed:28463111). Expressed in roots, stems, leaves, developing embryo, siliques, inflorescences, provascular tissue, shoot apical meristem (SAM) and adaxial (upper) sides of lateral organ primordia. Observed in the floral meristem, the adaxial side of sepal primordia, and the provascular tissue (PubMed:26390296). Up-regulated by REV (PubMed:22781836). Defects in meristem formation. Shoot apical meristem (SAM) terminates to a flat meristem, a small radially symmetric pin-like structure that lacks a vascular strand, a radially symmetric leaf, a single leaf or two leaves fused on their adaxial sides. Abnormal ovules and embryos. The double mutant pnh-2 han-2 has smaller inflorescence meristems (IM) and taller floral meristems (FM) leading to fewer petals (PubMed:26390296). Plants overexpressing AGO10 show upward curling of leaf blades and double cotyledon-like structures. Belongs to the argonaute family. Ago subfamily.