Nuclear processing and export of microRNAs in Arabidopsis

doi:10.1073/pnas.0405570102

Nuclear processing and export of microRNAs in Arabidopsis

^†Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018; and ^‡Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, 78026 Versailles Cedex, France

Edited by James E. Dahlberg, University of Wisconsin Medical School, Madison, WI (received for review August 2, 2004)

Abstract

In mammalian cells, the nuclear export receptor, Exportin 5 (Exp5), exports pre-microRNAs (pre-miRNAs) as well as tRNAs into the cytoplasm. In this study, we examined the function of HASTY (HST), the Arabidopsis ortholog of Exp5, in the biogenesis of miRNAs and tRNAs. In contrast to mammals, we found that miRNAs exist as single-stranded 20- to 21-nt molecules in the nucleus in Arabidopsis. This observation is consistent with previous studies indicating that proteins involved in miRNA biogenesis are located in the nucleus in Arabidopsis. Although miRNAs exist in the nucleus, a majority accumulate in the cytoplasm. Interestingly, loss-of-function mutations in HST reduced the accumulation of most miRNAs but had no effect on the accumulation of tRNAs and endogenous small interfering RNAs, or on transgene silencing. In contrast, a mutation in PAUSED (PSD), the Arabidopsis ortholog of the tRNA export receptor, Exportin-t, interfered with the processing of tRNA-Tyr but did not affect the accumulation or nuclear export of miRNAs. These results demonstrate that HST and PSD do not share RNA cargos in nuclear export and strongly suggest that there are multiple nuclear export pathways for these small RNAs in Arabidopsis.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: spoethig{at}sas.upenn.edu.
Author contributions: M.Y.P. and R.S.P. designed research; M.Y.P. and A.G.-S. performed research; G.W. and H.V. contributed new reagents/analytic tools; M.Y.P. and R.S.P. analyzed data; and R.S.P. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ds, double-stranded; miRNA, microRNA; siRNA, small interfering RNA; ss, single-stranded.