Shoot-supplied ammonium targets the root auxin influx carrier AUX1 and inhibits lateral root emergence in Arabidopsis

Authors

  • BAOHAI LI,

    1. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
    2. Graduate School of Chinese Academy of Science, Beijing 100081, China
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  • QING LI,

    1. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
    2. Graduate School of Chinese Academy of Science, Beijing 100081, China
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  • YANHUA SU,

    1. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
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  • HAO CHEN,

    1. Donald Danforth Plant Science Center, St. Louis, Missouri 63132, USA
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  • LIMING XIONG,

    1. Donald Danforth Plant Science Center, St. Louis, Missouri 63132, USA
    2. Plant Stress Genomics Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
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  • GUOHUA MI,

    1. College of Resources and Environmental Science, China Agricultural University, Beijing 100094, China
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  • HERBERT J. KRONZUCKER,

    1. Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada
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  • WEIMING SHI

    Corresponding author
    1. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
      W. Shi. Fax: +86 25 86881000; e-mail: wmshi@issas.ac.cn
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W. Shi. Fax: +86 25 86881000; e-mail: wmshi@issas.ac.cn

ABSTRACT

Deposition of ammonium (NH4+) from the atmosphere is a substantial environmental problem. While toxicity resulting from root exposure to NH4+ is well studied, little is known about how shoot-supplied ammonium (SSA) affects root growth. In this study, we show that SSA significantly affects lateral root (LR) development. We show that SSA inhibits lateral root primordium (LRP) emergence, but not LRP initiation, resulting in significantly impaired LR number. We show that the inhibition is independent of abscisic acid (ABA) signalling and sucrose uptake in shoots but relates to the auxin response in roots. Expression analyses of an auxin-responsive reporter, DR5:GUS, and direct assays of auxin transport demonstrated that SSA inhibits root acropetal (rootward) auxin transport while not affecting basipetal (shootward) transport or auxin sensitivity of root cells. Mutant analyses indicated that the auxin influx carrier AUX1, but not the auxin efflux carriers PIN-FORMED (PIN)1 or PIN2, is required for this inhibition of LRP emergence and the observed auxin response. We found that AUX1 expression was modulated by SSA in vascular tissues rather than LR cap cells in roots. Taken together, our results suggest that SSA inhibits LRP emergence in Arabidopsis by interfering with AUX1-dependent auxin transport from shoot to root.

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