Microsymbiont discrimination mediated by a host-secreted peptide in Medicago truncatula

• Published in: Proceedings of the National Academy of Sciences - PNAS 2017-06, Vol.114 (26), p.6848-6853
• Main Authors: Yang, Shengming, Wang, Qi, Fedorova, Elena, Liu, Jinge, Qin, Qiulin, Zheng, Qiaolin, Price, Paul A., Pan, Huairong, Wang, Dong, Griffitts, Joel S., Bisseling, Ton, Zhu, Hongyan
• Format: Article
• Language: English
• Subjects: Alfalfa; Apoptosis; Bacteria; Bacteroids; Biological Sciences; Cell death; Cloning; Differentiation; Discrimination; Ecological effects; Ecological niches; Endosymbionts; EPS; Genetic control; Host plants; Incompatibility; Laboratorium voor Moleculaire biologie; Laboratory of Molecular Biology; Legumes; Medicago truncatula; Nitrogen; Nitrogen fixation; Nitrogen-fixing bacteria; Nodules; Peptides; Root nodules; Senescence; Sinorhizobium meliloti; Symbiosis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1700460114

The legume–rhizobial symbiosis results in the formation of root nodules that provide an ecological niche for nitrogen-fixing bacteria. However, plant–bacteria genotypic interactions can lead to wide variation in nitrogen fixation efficiency, and it is not uncommon that a bacterial strain forms functional (Fix⁺) nodules on one plant genotype but nonfunctional (Fix⁻) nodules on another. Host genetic control of this specificity is unknown. We herein report the cloning of the Medicago truncatula NFS1 gene that regulates the fixation-level incompatibility with the microsymbiont Sinorhizobium meliloti Rm41. We show that NFS1 encodes a nodulespecific cysteine-rich (NCR) peptide. In contrast to the known role of NCR peptides as effectors of endosymbionts’ differentiation to nitrogen-fixing bacteroids, we demonstrate that specific NCRs control discrimination against incompatible microsymbionts. NFS1 provokes bacterial cell death and early nodule senescence in an allele-specific and rhizobial strain-specific manner, and its function is dependent on host genetic background.