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Int. J. Mol. Sci. 2016, 17(7), 1060;

Molecular Signals Controlling the Inhibition of Nodulation by Nitrate in Medicago truncatula

Division of Plant Science, Research School of Biology, Australian National University, Canberra ACT 2601, Australia
These authors contributed equally to this work.
Current address: Medtronic Bakken Research Centre B.V., 6229 GW Maastricht, The Netherlands
Current address: Wageningen UR Plant Breeding, P.O. Box 386, 6700 AJ Wageningen, The Netherlands
Current address: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081, China
Author to whom correspondence should be addressed.
Academic Editor: Peter M. Gresshoff
Received: 17 May 2016 / Revised: 22 June 2016 / Accepted: 24 June 2016 / Published: 2 July 2016
(This article belongs to the Special Issue Molecular Signals in Nodulation Control)
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The presence of nitrogen inhibits legume nodule formation, but the mechanism of this inhibition is poorly understood. We found that 2.5 mM nitrate and above significantly inhibited nodule initiation but not root hair curling in Medicago trunatula. We analyzed protein abundance in M. truncatula roots after treatment with either 0 or 2.5 mM nitrate in the presence or absence of its symbiont Sinorhizobium meliloti after 1, 2 and 5 days following inoculation. Two-dimensional gel electrophoresis combined with mass spectrometry was used to identify 106 differentially accumulated proteins responding to nitrate addition, inoculation or time point. While flavonoid-related proteins were less abundant in the presence of nitrate, addition of Nod gene-inducing flavonoids to the Sinorhizobium culture did not rescue nodulation. Accumulation of auxin in response to rhizobia, which is also controlled by flavonoids, still occurred in the presence of nitrate, but did not localize to a nodule initiation site. Several of the changes included defense- and redox-related proteins, and visualization of reactive oxygen species indicated that their induction in root hairs following Sinorhizobium inoculation was inhibited by nitrate. In summary, the presence of nitrate appears to inhibit nodulation via multiple pathways, including changes to flavonoid metabolism, defense responses and redox changes. View Full-Text
Keywords: auxin; flavonoid; nitrate; nodulation; proteomics; reactive oxygen species auxin; flavonoid; nitrate; nodulation; proteomics; reactive oxygen species

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van Noorden, G.E.; Verbeek, R.; Dinh, Q.D.; Jin, J.; Green, A.; Ng, J.L.P.; Mathesius, U. Molecular Signals Controlling the Inhibition of Nodulation by Nitrate in Medicago truncatula. Int. J. Mol. Sci. 2016, 17, 1060.

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