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Mol Cells. 2017 Jan;40(1):17-23. doi: 10.14348/molcells.2017.2211. Epub 2017 Jan 31.

MAP Kinase-Mediated Negative Regulation of Symbiotic Nodule Formation in Medicago truncatula.

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  • 1Department of Life Sciences, POSTECH Biotech Center, Pohang University of Science and Technology, Pohang 37673, Korea.
  • 2Department of Biology, Chungbuk National University, Cheongju 28644, Korea.
  • 3Institute of Plant Sciences-Paris-Saclay (IPS2), CNRS, INRA, Univ Paris-Sud, Univ Paris-Diderot, Univ d'Evry, Université Paris-Saclay, Bâtiment 630, 91190 Gif-sur-Yvette, France.


Mitogen-activated protein kinase (MAPK) signaling cascades play critical roles in various cellular events in plants, including stress responses, innate immunity, hormone signaling, and cell specificity. MAPK-mediated stress signaling is also known to negatively regulate nitrogen-fixing symbiotic interactions, but the molecular mechanism of the MAPK signaling cascades underlying the symbiotic nodule development remains largely unknown. We show that the MtMKK5-MtMPK3/6 signaling module negatively regulates the early symbiotic nodule formation, probably upstream of ERN1 (ERF Required for Nodulation 1) and NSP1 (Nod factor Signaling Pathway 1) in Medicago truncatula. The overexpression of MtMKK5 stimulated stress and defense signaling pathways but also reduced nodule formation in M. truncatula roots. Conversely, a MAPK specific inhibitor, U0126, enhanced nodule formation and the expression of an early nodulation marker gene, MtNIN. We found that MtMKK5 directly activates MtMPK3/6 by phosphorylating the TEY motif within the activation loop and that the MtMPK3/6 proteins physically interact with the early nodulation-related transcription factors ERN1 and NSP1. These data suggest that the stress signaling-mediated MtMKK5/MtMPK3/6 module suppresses symbiotic nodule development via the action of early nodulation transcription factors.


MAPK; legume; nitrogen fixation; signal transduction; symbiosis

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