Editor: Keith Chater
The roles of extracellular proteins, polysaccharides and signals in the interactions of rhizobia with legume roots
Article first published online: 15 DEC 2009
© 2010 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved
FEMS Microbiology Reviews
Special Issue: Extracellular Biology
Volume 34, Issue 2, pages 150–170, March 2010
How to Cite
Downie, J. A. (2010), The roles of extracellular proteins, polysaccharides and signals in the interactions of rhizobia with legume roots. FEMS Microbiology Reviews, 34: 150–170. doi: 10.1111/j.1574-6976.2009.00205.x
- Issue published online: 1 FEB 2010
- Article first published online: 15 DEC 2009
- Received 7 September 2009; revised 18 November 2009; accepted 23 November 2009.Final version published online 8 January 2010.
- quorum sensing;
- Nod factor
Rhizobia adopt many different lifestyles including survival in soil, growth in the rhizosphere, attachment to root hairs and infection and growth within legume roots, both in infection threads and in nodules where they fix nitrogen. They are actively involved in extracellular signalling to their host legumes to initiate infection and nodule morphogenesis. Rhizobia also use quorum-sensing gene regulation via N-acyl-homoserine lactone signals and this can enhance their interaction with legumes as well as their survival under stress and their ability to induce conjugation of plasmids and symbiotic islands, thereby spreading their symbiotic capacity. They produce several surface polysaccharides that are critical for attachment and biofilm formation; some of these polysaccharides are specific for their growth on root hairs and can considerably enhance their ability to infect their host legumes. Different rhizobia use several different types of protein secretion mechanisms (Types I, III, IV, V and VI), and many of the secreted proteins play an important role in their interaction with plants. This review summarizes many of the aspects of the extracellular biology of rhizobia, in particular in relation to their symbiotic interaction with legumes.