期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 109, 期 34, 页码 13859-13864出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1205171109
关键词
lysin motif proteins; plant-microbe interactions; symbiotic signalling; lysin motif receptor-like kinase; non-self recognition
资金
- Danish National Research Foundation
- European Research Council
Lipochitin oligosaccharides called Nod factors function as primary rhizobial signal molecules triggering legumes to develop new plant organs: root nodules that host the bacteria as nitrogen-fixing bacteroids. Here, we show that the Lotus japonicus Nod factor receptor 5 (NFR5) and Nod factor receptor 1 (NFR1) bind Nod factor directly at high-affinity binding sites. Both receptor proteins were posttranslationally processed when expressed as fusion proteins and extracted from purified membrane fractions of Nicotiana benthamiana or Arabidopsis thaliana. The N-terminal signal peptides were cleaved, and NFR1 protein retained its in vitro kinase activity. Processing of NFR5 protein was characterized by determining the N-glycosylation patterns of the ectodomain. Two different glycan structures with identical composition, Man(3)XylFucGlcNAc(4), were identified by mass spectrometry and located at amino acid positions N68 and N198. Receptor-ligand interaction was measured by using ligands that were labeled or immobilized by application of chemo-selective chemistry at the anomeric center. High-affinity ligand binding was demonstrated with both solid-phase and free solution techniques. The K-d values obtained for Nod factor binding were in the nanomolar range and comparable to the concentration range sufficient for biological activity. Structure-dependent ligand specificity was shown by using chitin oligosaccharides. Taken together, our results suggest that ligand recognition through direct ligand binding is a key step in the receptor-mediated activation mechanism leading to root nodule development in legumes.
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