Phloem-Mobile Aux/IAA Transcripts Target to the Root Tip and Modify Root Architecture

Authors

  • Michitaka Notaguchi,

    1. Department of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA
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    • Present address: JST ERATO Higashiyama Live-Holonics Project, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, auAichi 464-8602, Japan

  • Shmuel Wolf,

    1. The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture and the Otto Warburg Minerva Center for Agricultural Biotechnology, The Hebrew University of Jerusalem, The Robert H. Smith Faculty of Agriculture, Food and Environment, Rehovot 76100, Israel
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  • William J. Lucas

    Corresponding author
    1. Department of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA
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Tel: +1 530 752 1093; Fax: +1 530 752 5410; E-mail: wjlucas@ucdavis.edu

Abstract

In plants, the phloem is the component of the vascular system that delivers nutrients and transmits signals from mature leaves to developing sink tissues. Recent studies have identified proteins, mRNA, and small RNA within the phloem sap of several plant species. It is now of considerable interest to elucidate the biological functions of these potential long-distance signal agents, to further our understanding of how plants coordinate their developmental programs at the whole-plant level. In this study, we developed a strategy for the functional analysis of phloem-mobile mRNA by focusing on IAA transcripts, whose mobility has previously been reported in melon (Cucumis melo cv. Hale's Best Jumbo). Indoleacetic acid (IAA) proteins are key transcriptional regulators of auxin signaling, and are involved in a broad range of developmental processes including root development. We used a combination of vasculature-enriched sampling and hetero-grafting techniques to identify IAA18 and IAA28 as phloem-mobile transcripts in the model plant Arabidopsis thaliana. Micro-grafting experiments were used to confirm that these IAA transcripts, which are generated in vascular tissues of mature leaves, are then transported into the root system where they negatively regulate lateral root formation. Based on these findings, we present a model in which auxin distribution, in combination with phloem-mobile Aux/IAA transcripts, can determine the sites of auxin action.

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