Letter | Published:

Spatially restricted microRNA directs leaf polarity through ARGONAUTE1

Abstract

Gene regulation by RNA interference requires the functions of the PAZ domain protein Argonaute. In plants, mutations in ARGONAUTE1 (AGO1) are associated with distinctive developmental defects that suggest a role for microRNA (miRNA) in organ polarity. Potential targets of miRNA regulation are the homeodomain/leucine zipper genes PHABULOSA (PHB) and PHAVOLUTA (PHV)1. These genes are expressed in a polar fashion in leaf primordia and are required for adaxial cell fate2,3. Here we show that a 21-nucleotide miRNA that directs cleavage of PHB/PHV messenger RNA accumulates first in the embryonic meristem, and then in the abaxial domain of the developing leaf. miRNA distribution is disrupted by mutations in AGO1, indicating that AGO1 affects the regulation of miRNA. In addition, interactions between homeodomain/leucine zipper genes and an allelic series of ago1 indicate that miRNA acts as a signal to specify leaf polarity.

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Acknowledgements

We thank K. Barton, B. Reinhart and D. Bartel for sharing unpublished data, M. Timmermans and M. Byrne for discussion and critical reading of the manuscript. We also thank T. Mulligan for plant care, and B. Lehner, S. Gao, S. Morgan, R. Shen, R. Umamaheswari and A. Tang, for laboratory assistance. We thank C. Dean, S. Poethig, J. Levin, R. Howden and J. Moore for alerting us to new alleles of ago1. This work was supported by a postdoctoral fellowship from the Cold Spring Harbor Association (C.K.), and grants from the National Science Foundation and the NIH to R.M.

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Correspondence to Robert A. Martienssen.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary figure

a) RT-PCR of FIL, KAN1 and ERECTA from inflorescences of dcl1-9/rev-6 doubles, dcl1-9 and rev-6 homozygotes and three dilutions of wild type. Lower levels of FIL expression are seen in the dcl1-9/rev-6 double; b) Control hybridization of wild type inflorescence with the sense pre-miRNA probe. (JPG 61 kb)

Supplementary figure legend (DOC 19 kb)

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Figure 1: Mutations in AGO1 are adaxialized and mutations in REV are enhanced by ago1 and dcl1-9.
Figure 2: Reporter gene expression in ago1-10 demonstrates adaxialization.
Figure 3: Transcripts from miR165 accumulate in the embryonic meristem and on the abaxial side of the leaf.

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