title: Identification of nodule-specific cysteine-rich plant peptides in endosymbiotic bacteria.
abstract: The symbiosis of Medicago truncatula with Sinorhizobium meliloti or Sinorhizobium medicae soil bacteria results in the formation of root nodules where bacteria inside the plant cells are irreversibly converted to polyploid, nondividing nitrogen-fixing bacteroids. Bacteroid differentiation is host-controlled and the plant effectors are symbiosis-specific secreted plant peptides. In the M. truncatula genome there are more than 600 symbiotic peptide genes including 500 small genes coding for nodule-specific cysteine-rich (NCR) peptides. While NCR transcripts represent >5% of the nodule transcriptome, the existence of only eight NCR peptides has been demonstrated so far. The predicted NCRs are secreted peptides targeted to the endosymbionts. Correspondingly, all the eight detected peptides were present in the bacteroids. Here, we report on large-scale detection of NCR peptides from nodules and from isolated, semipurified endosymbionts at various stages of their differentiation. In total 138 NCRs were detected in the bacteroids; 38 were cationic while the majority was anionic. The presence of early NCRs in nitrogen-fixing bacteroids indicates their high stability, and their long-term maintenance suggests persisting biological roles in the bacteroids.
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Hajnalka
authors.initials: H
authors.lastname: Durgo
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Eva
authors.initials: E
authors.lastname: Klement
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Eva
authors.initials: E
authors.lastname: Hunyadi-Gulyas
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Szucs
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Kereszt
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.|Department of Pharmaceutical Chemistry, University California San Francisco, CA, USA.
authors.forename: Katalin F
authors.initials: KF
authors.lastname: Medzihradszky
authors.affiliation: Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Eva
authors.initials: E
authors.lastname: Kondorosi
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000235:genetics; D046913:Medicago truncatula / Q000378:metabolism* / Q000382:microbiology*; D053204:Root Nodules, Plant / Q000378:metabolism* / Q000382:microbiology*; D016962:Sinorhizobium meliloti / Q000502:physiology*; D013559:Symbiosis
keywords: Bacteroid; MS; Medicago truncatula; NCR-peptides; Plant proteomics; Symbiosis