JXB Advance Access originally published online on December 6, 2008
Journal of Experimental Botany 2009 60(2):581-590; doi:10.1093/jxb/ern302
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© 2008 The Author(s).
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RESEARCH PAPER |
Delayed maturation of nodules reduces symbiotic effectiveness of the Lotus japonicus–Rhizobium sp. NGR234 interaction
Laboratoire de Biologie Moléculaire des Plantes Supérieures (LBMPS), Université de Genève, 30 Quai Ernest-Ansermet, Sciences III, CH-1211 Genève 4, Switzerland
1Département de Botanique et de Biologie Végétale, Université de Genève, 30 Quai Ernest-Ansermet, Sciences III, CH-1211 Genève 4, Switzerland
* To whom correspondence should be addressed. E-mail: william.deakin{at}unige.ch
Lotus japonicus, a model legume, develops an efficient, nitrogen-fixing symbiosis with Mesorhizobium loti that promotes plant growth. Lotus japonicus also forms functional nodules with Rhizobium sp. NGR234 and R. etli. Yet, in a plant defence-like reaction, nodules induced by R. etli quickly degenerate, thus limiting plant growth. In contrast, nodules containing NGR234 are long-lasting. It was found that NGR234 initiates nodule formation in a similar way to M. loti MAFF303099, but that the nodules which develop on eleven L. japonicus ecotypes are less efficient in fixing nitrogen. Detailed examination of nodulation of L. japonicus cultivar MG-20 revealed that symbiosomes formed four weeks after inoculation by NGR234 are enlarged in comparison with MAFF303099 and contain multiple bacteroids. Nevertheless, nodules formed by NGR234 fix sufficient nitrogen to avoid rejection by the plant. With time, these nodules develop into fully efficient organs containing bacteroids tightly enclosed in symbiosome membranes, just like those formed by M. loti MAFF303099. This work demonstrates the usefulness of using the well-characterized micro-symbiont NGR234 to study symbiotic signal exchange in the later stages of rhizobia–legume symbioses, especially given the large range of bacterial (NGR234) and plant (L. japonicus) mutants that are available.
Key words: Infection, Mesorhizobium, nodulation, persistence, rhizobia, senescence, symbiosis, symbiosomes
Received 7 August 2008; Revised 24 October 2008 Accepted 31 October 2008