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Symbiotic use of pathogenic strategies: rhizobial protein secretion systems

Nature Reviews Microbiology volume 7, pages 312–320 (2009)Cite this article

Abstract

Rhizobia — a diverse group of soil bacteria — induce the formation of nitrogen-fixing nodules on the roots of legumes. Nodulation begins when the roots initiate a molecular dialogue with compatible rhizobia in the soil. Most rhizobia reply by secreting lipochitooligosaccharidic nodulation factors that enable entry into the legume. A molecular exchange continues, which, in compatible interactions, permits rhizobia to invade root cortical cells, differentiate into bacteroids and fix nitrogen. Rhizobia also use additional molecular signals, such as secreted proteins or surface polysaccharides. One group of proteins secreted by rhizobia have homologues in bacterial pathogens and may have been co-opted by rhizobia for symbiotic purposes.

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Figure 1: Nodule development processes.
Figure 2: Regulation of rhizobial protein secretion systems.
Figure 3: Functions of rhizobial effectors.

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Acknowledgements

We are grateful to M. Göttfert, W. D'Haeze, H. Kobayashi and G. Walker for their critical reviews of the manuscript. J. Michiels allowed us to cite his unpublished data. We thank S. Ardissone, N. Bakkou, J. Gay-Fraret, K. Kambara, P. Lariguet, A. Le Quéré and O. Schumpp for discussions and sharing their unpublished data. We are indebted to Y.-Y. Aung and D. Gerber for their unstinting help with our work. We apologize to the numerous researchers whose work could not be cited owing to space limitations. Financial support from the Fonds National Suisse de la Recherche Scientifique (projects 3100AO-104097 and 3100A0-116858) is gratefully acknowledged.

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  1. William J. Deakin and William J. Broughton are at the LBMPS, University of Geneva, 30, quai Ernest-Ansermet — Sciences III, CH-1211 Genève 4, Geneva, Switzerland.,

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DATABASES

Entrez Genome Project

Agrobacterium tumefaciens

Bradyrhizobium japonicum USDA110

Glycine max

Lotus japonicus

Medicago sativa

Medicago truncatula

Mesorhizobium loti

Phaseolus vulgaris

Pseudomonas syringae

Rhizobium leguminosarum

Rhizobium sp. NGR234

Shigella flexneri

Sinorhizobium meliloti

Vigna unguiculata

FURTHER INFORMATION

LBMPS

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Deakin, W., Broughton, W. Symbiotic use of pathogenic strategies: rhizobial protein secretion systems. Nat Rev Microbiol 7, 312–320 (2009). https://doi.org/10.1038/nrmicro2091

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