Involved in the RNA silencing pathway. Cleaves double-stranded RNA to produce small interfering RNAs (siRNAs) which target the selective destruction of complementary RNAs. Required for the production of 21 nucleotide siRNAs. Regulates shoot apical meristem (SAM) initiation and maintenance, leaf polarization and lemma polarity through the trans-acting siRNAS (ta-siRNAs) pathway, which probably modulate the expression of the ARF2, ARF3, ARF4, ARF14 and ARF15 genes. Can process endogenous 21 nucleotide siRNAs derived from an imperfect inverted repeat. May not be involved in microRNAs (miRNAs) production. May interact with ARGONAUTE1 or PINHEAD through their common PAZ domains. Expressed in roots, leaf blades, leaf sheaths, shoot apices and spikelets. Formation of an incomplete shoot apical meristem (SAM), abnormal vegetative development with alteration of adaxial/abaxial polarity in both coleoptiles and the first leaves. Abnormal spikelet morphology with disruption of organ identity and lemma polarity. Belongs to the helicase family. Dicer subfamily.