MtCRE1-dependent cytokinin signaling integrates bacterial and plant cues to coordinate symbiotic nodule organogenesis in Medicago truncatula

Authors

  • Julie Plet,

    1. Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique, 91198 Gif sur Yvette Cedex, France
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  • Anton Wasson,

    1. Australian Research Council Centre of Excellence for Integrative Legume Research, Division of Plant Science, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
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  • Federico Ariel,

    1. Instituto de Agrobiotecnología del Litoral, Consejo Nacional de Investigaciones Científicas y Técnicas – Universidad Nacional del Litoral (CONICET-UNL), Ciudad Universitaria, 3000 Santa Fe, Argentina
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  • Christine Le Signor,

    1. Unité Mixte de Recherche en Génétique et Ecophysiologie des Légumineuses à Graines, Institut National de la Recherche Agronomique, Dijon, France
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  • David Baker,

    1. John Innes Genome Laboratory, Norwich NR4 7UH, UK
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  • Ulrike Mathesius,

    1. Australian Research Council Centre of Excellence for Integrative Legume Research, Division of Plant Science, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
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  • Martin Crespi,

    1. Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique, 91198 Gif sur Yvette Cedex, France
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  • Florian Frugier

    Corresponding author
    1. Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique, 91198 Gif sur Yvette Cedex, France
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(fax +33 169 823654; e-mail frugier@isv.cnrs-gif.fr).

Summary

Phytohormonal interactions are essential to regulate plant organogenesis. In response to the presence of signals from symbiotic bacteria, the Nod factors, legume roots generate a new organ: the nitrogen-fixing nodule. Analysis of mutants in the Medicago truncatula CRE1 cytokinin receptor and of the MtRR4 cytokinin primary response gene expression pattern revealed that cytokinin acts in initial cortical cell divisions and later in the transition between meristematic and differentiation zones of the mature nodule. MtCRE1 signaling is required for activation of the downstream nodulation-related transcription factors MtERN1, MtNSP2 and MtNIN, as well as to regulate expression and accumulation of PIN auxin efflux carriers. Whereas the MtCRE1 pathway is required to allow the inhibition of polar auxin transport in response to rhizobia, nodulation is still negatively regulated by the MtEIN2/SICKLE-dependent ethylene pathway in cre1 mutants. Hence, MtCRE1 signaling acts as a regulatory knob, integrating positive plant and bacterial cues to control legume nodule organogenesis.

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