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bioRxiv · 10.1101/2025.09.29.679184

EPP1 couples receptor activation to cytoplasmic signaling in root nodule symbiosis

Noergaard, M.·Abel, N.·Birkeskov, E.·Landry, D.·Stougaard, J.·Andersen, K. R.
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Abstract

Legume symbiosis with nitrogen-fixing bacteria is controlled by a cascade of signaling events leading to root nodule development. While plant cell-surface receptors initiate this process, the link between receptors and cytoplasmic signaling components remains unclear. Here we identify Early Phosphorylated Protein 1 (EPP1) as a central mediator of this pathway. EPP1 is recruited to the activated SYMRK receptor, where it is phosphorylated on a key serine residue, an event essential and sufficient to propagate symbiotic signaling. We provide structural and functional validation of the SYMRK-EPP1 signaling complex and demonstrate that EPP1 is required for root nodule formation. Synthetic engineering of the SYMRK-EPP1 interaction bypasses the need for symbiotic bacteria to initiate the pathway and triggers nodule organogenesis. These findings establish EPP1 as a crucial cytoplasmic component between receptor activation and intracellular signaling, advancing our understanding of nitrogen-fixing symbiosis.

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Noergaard, M., Abel, N., Birkeskov, E., Landry, D., Stougaard, J., Andersen, K. R.. 2025-10-01. EPP1 couples receptor activation to cytoplasmic signaling in root nodule symbiosis. https://doi.org/10.1101/2025.09.29.679184

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