Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis
Authors
Lodwig, Emma M.Hosie, Arthur H.F.
Bourdes, Alex
Findlay, K.
Allaway, D.
Karunakaran, R.
Downie, J. A.
Poole, Philip S.
Issue Date
2003
Metadata
Show full item recordAbstract
The biological reduction of atmospheric N2 to ammonium (nitrogen fixation) provides about 65% of the biosphere's available nitrogen. Most of this ammonium is contributed by legume–rhizobia symbioses1, which are initiated by the infection of legume hosts by bacteria (rhizobia), resulting in formation of root nodules. Within the nodules, rhizobia are found as bacteroids, which perform the nitrogen fixation: to do this, they obtain sources of carbon and energy from the plant, in the form of dicarboxylic acids2, 3. It has been thought that, in return, bacteroids simply provide the plant with ammonium. But here the authors show that a more complex amino-acid cycle is essential for symbiotic nitrogen fixation by Rhizobium in pea nodules. The plant provides amino acids to the bacteroids, enabling them to shut down their ammonium assimilation. In return, bacteroids act like plant organelles to cycle amino acids back to the plant for asparagine synthesis. The mutual dependence of this exchange prevents the symbiosis being dominated by the plant, and provides a selective pressure for the evolution of mutualism.Citation
Lodwig, E.M., Hosie, A.H.F., Bourdes, A. (2003) 'Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis', Nature, 422, pp.722-726Publisher
Nature Publishing GroupJournal
NatureAdditional Links
http://www.nature.com/doifinder/10.1038/nature01527Type
ArticleLanguage
enISSN
0028-0836ae974a485f413a2113503eed53cd6c53
10.1038/nature01527