title: Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant.
abstract: Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula.
authors.affiliation: National Agricultural Research and Innovation Centre, Agricultural Biotechnology Institute, Gödöllő 2100, Hungary;
authors.forename: Beatrix
authors.initials: B
authors.lastname: Horváth
authors.affiliation: National Agricultural Research and Innovation Centre, Agricultural Biotechnology Institute, Gödöllő 2100, Hungary;
authors.forename: Ágota
authors.initials: Á
authors.lastname: Domonkos
authors.affiliation: Institute of Biochemistry, Biological Research Center, Szeged 6726, Hungary;
authors.forename: Attila
authors.identifier: http://orcid.org/0000-0002-4421-6554
authors.initials: A
authors.lastname: Kereszt
authors.affiliation: Institute of Biochemistry, Biological Research Center, Szeged 6726, Hungary;
authors.forename: Attila
authors.initials: A
authors.lastname: Szűcs
authors.affiliation: Institute of Biochemistry, Biological Research Center, Szeged 6726, Hungary;
authors.forename: Edit
authors.initials: E
authors.lastname: Ábrahám
authors.affiliation: Cellular Imaging Laboratory, Biological Research Center, Szeged 6726, Hungary;
authors.forename: Ferhan
authors.initials: F
authors.lastname: Ayaydin
authors.affiliation: Department of Plant Anatomy, Eötvös Loránd University, Budapest 1117, Hungary;
authors.forename: Károly
authors.initials: K
authors.lastname: Bóka
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401;
authors.forename: Yuhui
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401;
authors.forename: Rujin
authors.initials: R
authors.lastname: Chen
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401; Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Murray
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401;
authors.forename: Michael K
authors.initials: MK
authors.lastname: Udvardi
authors.affiliation: Institute of Biochemistry, Biological Research Center, Szeged 6726, Hungary;
authors.forename: Éva
authors.initials: É
authors.lastname: Kondorosi
authors.affiliation: National Agricultural Research and Innovation Centre, Agricultural Biotechnology Institute, Gödöllő 2100, Hungary; kalo@abc.hu.
authors.forename: Péter
authors.initials: P
authors.lastname: Kaló
mesh_terms: D003545:Cysteine / Q000737:chemistry*; D046913:Medicago truncatula / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009586:Nitrogen Fixation / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry / Q000502:physiology*; D013559:Symbiosis
chemical_list: D010940:Plant Proteins; D003545:Cysteine
keywords: Sinorhizobium; bacteroid differentiation; ineffective nodules; senescence; symbiotic host peptides