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Post-transcriptional gene silencing mediated by microRNAs(miRNAs)modulates numerous develop-mental and stress response pathways.For the last two decades,HASTY(HST),the ortholog of human EX-PORTIN 5,was considered to be a candidate protein that exports plant miRNAs from the nucleus to the cytoplasm.Here,we report that HST functions in the miRNA pathway independent of its cargo-exporting activity in Arabidopsis.We found that Arabidopsis mutants with impaired HST shuttling exhibit normal sub-cellular distribution of miRNAs.Interestingly,protein-protein interaction and microscopy assays showed that HST directly interacts with the microprocessor core component DCL1 through its N-terminal domain.Moreover,mass spectrometry analysis revealed that HST also interacts independently of its N-terminal domain with the mediator complex subunit MED37.Further experiments revealed that HST could act as a scaffold to facilitate the recruitment of DCL1 to genomic MIRNA loci by stabilizing the DCL1-MED37 com-plex,which in turn promotes the transcription and proper processing of primary miRNA transcripts(pri-miRNAs).Taken together,these results suggest that HST is likely associated with the formation of the miRNA biogenesis complex at MIRNA genes,promoting the transcription and processing of pri-miRNAs rather than the direct export of processed miRNAs from the nucleus.