The study, published in PNAS, focuses on the Nod Factor Receptor 5 (NFR5), a plant receptor that recognizes signals from symbiotic bacteria and triggers the formation of nitrogen-fixing nodules on plant roots. NFR5, found in legumes such as Lotus japonicus, is known to partner with NFR1, another receptor protein, to mediate the symbiotic relationship between plants and bacteria. While NFR1’s signaling role depends on its active kinase domain, NFR5 is a pseudokinase without catalytic activity, leaving its role in the symbiotic signaling process unclear - until now.

Simon Hansen in the group of Kasper Røjkjær Andersen has now solved the crystal structure of the intracellular domain of NFR5 and identified a crucial juxtamembrane motif - a hydrophobic region located just inside the cell. This motif, consisting of two α-helices named αA and αA', was found to mediate interactions between individual NFR5 molecules and between NFR5 and NFR1. These interactions are essential for triggering the signaling pathway that leads to nodule formation.

The study's findings reveal that this juxtamembrane motif is highly conserved across various plant species, suggesting that it plays a broader role in plant-microbe interactions beyond legumes. Mutations that disrupt this motif were shown to prevent the formation of root nodules, underlining its importance in symbiosis.

The discovery has implications for agricultural science, particularly in the ongoing efforts to engineer nitrogen-fixing symbiosis into non-legume crops like wheat or corn. By understanding the structural and functional mechanisms of receptors like NFR5, scientists are one step closer to developing crops that can naturally fix nitrogen, potentially reducing the need for synthetic fertilizers and promoting sustainable agriculture.

The research paper:

A conserved juxtamembrane motif in plant NFR5 receptors is essential for root nodule symbiosis
Simon Boje Hansen, Thi Bich Luu, Kira Gysel, Damiano Lironi, Christina Krönauer, Henriette Rübsam, Ingeborg Bitsch Jensen, Magdalini Tsitsikli, Thea Gramkov Birkefeldt, Alen Trgovcevic, Jens Stougaard, Simona Radutoiu, and Kasper Røjkjær Andersen

PNAS 2024 Vol. 121 No. 0 e2405671121 https://doi.org/10.1073/pnas.2405671121

SUPPLEMENTARY INFORMATION

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Study type:

Research article

External funding:

This work is funded by the Danish Council for Independent Research (9040-00175B and 3103-00137B) and the project Enabling Nutrient Symbioses in Agriculture (ENSA), which is funded by Bill & Melinda Gates Agricultural Innovations (INV- 57461), the Bill & Melinda Gates Foundation and the Foreign, Commonwealth and Development Office (INV-55767).

Conflict of interest:

Some findings from this article are considered for a patent application.

Contact information:

Professor Kasper Røjkjær Andersen
Department of Molecular Biology and Genetics
Aarhus University
kra@mbg.au.dk

Professor Simona Radutoiu
Department of Molecular Biology and Genetics
Aarhus University
radutoiu@mbg.au.dk