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

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. © 2011 Blackwell Publishing Ltd.

Citation
LI, B., LI, Q., SU, Y., CHEN, H., XIONG, L., MI, G., … SHI, W. (2011). Shoot-supplied ammonium targets the root auxin influx carrier AUX1 and inhibits lateral root emergence inArabidopsis. Plant, Cell & Environment, 34(6), 933–946. doi:10.1111/j.1365-3040.2011.02295.x

Acknowledgements
We thank Professors Malcolm Bennett (University of Nottingham), Ben Scheres (Utrecht University) and Tom Guilfoyle (University of Missouri) for providing the transgenic lines of Arabidopsis, and the Arabidopsis Biological Resource Center for the mutant seeds. We are grateful to Malcolm Bennett (University of Nottingham) for invaluable advice during designing and writing of the manuscript. We also thank other members of our team for helpful comments on the manuscript. This work was supported by the National Basic Research Program of China (2007CB109303), the National Natural Science Foundation of China (30771285) and the National Sciences and Engineering Research Council of Canada (NSERC, Discovery Grant 217277-2009).

Publisher
Wiley

Journal
Plant, Cell & Environment

DOI
10.1111/j.1365-3040.2011.02295.x

PubMed ID
21342208

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