Functions as component of microRNA (miRNA) and small interfering RNA (siRNA) biogenesis. May assist DCL1 and DCL4 to efficiently process and/or recruit the precursors of miRNAs and siRNAs. In the miRNA biogenesis pathway, associates with the DCL1 complex that processes primary miRNAs (pri-miRNAs) into miRNAs. Binds pri-miRNAs and precursor miRNAs (pre-miRNAs). Is required for the interaction between pri-miRNAs and DRB1 (PubMed:22802657). Required for general proper plant growth and, in particular, initiation of vascular development. Interacts genetically with AMP1, a glutamate carboxypeptidase involved in the regulation of meristem function (PubMed:16024589). Colocalizes with the splicing factor SR34 to subnuclear particles. Expressed in vasculature of cotyledons and leaves, young meristematic tissues, trichomes and pistils. Developmental defects, elongation defects of all organs, reduced plant height, triple cotyledons phenotype, reduced vascularization and infertility due to failure to produce pollen.