Functions probably in nuclear protein import, either by acting as autonomous nuclear transport receptor or as an adapter-like protein in association with other importin subunits (Probable). Involved in the regulation of the abscisic acid (ABA)-mediated pathway in response to cold or salt stress (PubMed:16889648). Involved in UV-B responses by regulating accumulation of UV-absorbing pigments through mediation of MYB4 nuclear transport (PubMed:17993626). Involved in trichome initiation by controlling GL1, GL2, GL3 and TTG1 transcription and may affect an upstream regulator of GL3 and disrupt complex function (PubMed:18713401, PubMed:19234066). Acts as negative regulator miRNA activity by regulating miRNA loading into AGO1 complexes (PubMed:21984696). Interacts with MYB4. Expressed in roots, epidermal and guard cells of leaves, stems and siliques. Early flowering and increased sensitivity to inhibition of seed germination and plant growth by exogenous ABA. Belongs to the importin beta family.