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Plant and Cell Physiology Advance Access originally published online on February 2, 2009
Plant and Cell Physiology 2009 50(3):626-634; doi:10.1093/pcp/pcp020
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

ARGONAUTE1 Acts in Arabidopsis Root Radial Pattern Formation Independently of the SHR/SCR Pathway

Shunsuke Miyashima, Takashi Hashimoto and Keiji Nakajima*

Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192 Japan

*Corresponding author: E-mail, k-nakaji{at}bs.naist.jp; Fax, +81-743-72-5529.


  Abstract

The formation of radially symmetric tissue patterns is one of the most basic processes in the development of vascular plants. In Arabidopsis thaliana, plant-specific GRAS-type transcription factors, SHORT-ROOT (SHR) and SCARECROW (SCR), are required for asymmetric cell divisions that separate two ground tissue cell layers, the endodermis and cortex, as well as for endodermal cell fate specification. While loss of SHR or SCR results in a single-layered ground tissue, radially symmetric cellular patterns are still maintained, suggesting that unknown regulatory mechanisms act independently of the SHR/SCR-dependent pathway. In this study, we identified a novel root radial pattern mutant and found that it is a new argonaute1 (ago1) allele. Multiple ago1 mutant alleles contained supernumerary ground tissue cell layers lacking a concentric organization, while expression patterns of SHR and SCR were not affected, revealing a previously unreported role for AGO1 in root ground tissue patterning. Analyses of ago1 scr double mutants demonstrated that the simultaneous loss of the two pathways caused a dramatic reduction in cellular organization and ground tissue identity as compared with the single mutants. Based on these results, we propose that highly symmetric root ground tissue patterns are maintained by the actions of two independent pathways, one using post-transcriptional regulation mediated by AGO1 and the other using the SHR/SCR transcriptional regulator.

Keywords: Arabidopsis thaliana - ARGONAUTE - Differentiation - MicroRNA - Pattern formation - Root.

Abbreviations: ACT, ACTIN; AGO1, ARGONAUTE1; CEI, cortex/endodermis initial; CLSM, confocal laser scanning microscopy; dpg, days post-germination; EMS, ethylmethane sulfonate; GFP, green fluorescent protein; HYL1, HYPONASTIC LEAVES1; LRC, lateral root cap; MiRNA, microRNA; MGP, MAGPIE; NUC, NUTCRACKER; qRT–PCR, quantitative reverse transcription–PCR; SCR, SCARECROW; SHR, SHORT-ROOT

(Received November 27, 2008; Accepted January 28, 2009)
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