title: Specificity in Legume-Rhizobia Symbioses.
abstract: Most species in the Leguminosae (legume family) can fix atmospheric nitrogen (N₂) via symbiotic bacteria (rhizobia) in root nodules. Here, the literature on legume-rhizobia symbioses in field soils was reviewed and genotypically characterised rhizobia related to the taxonomy of the legumes from which they were isolated. The Leguminosae was divided into three sub-families, the Caesalpinioideae, Mimosoideae and Papilionoideae.Bradyrhizobiumspp. were the exclusive rhizobial symbionts of species in the Caesalpinioideae, but data are limited. Generally, a range of rhizobia genera nodulated legume species across the two Mimosoideae tribes Ingeae and Mimoseae, butMimosaspp. show specificity towardsBurkholderiain central and southern Brazil,Rhizobium/Ensiferin central Mexico andCupriavidusin southern Uruguay. These specific symbioses are likely to be at least in part related to the relative occurrence of the potential symbionts in soils of the different regions. Generally, Papilionoideae species were promiscuous in relation to rhizobial symbionts, but specificity for rhizobial genus appears to hold at the tribe level for the Fabeae (Rhizobium), the genus level forCytisus(Bradyrhizobium),Lupinus(Bradyrhizobium) and the New Zealand nativeSophoraspp. (Mesorhizobium) and species level forCicer arietinum(Mesorhizobium),Listia bainesii(Methylobacterium) andListia angolensis(Microvirga). Specificity for rhizobial species/symbiovar appears to hold forGalega officinalis(Neorhizobium galegeaesv.officinalis), Galega orientalis(Neorhizobium galegeaesv.orientalis),Hedysarum coronarium(Rhizobium sullae),Medicago laciniata(Ensifer melilotisv.medicaginis),Medicago rigiduloides(Ensifer melilotisv.rigiduloides) andTrifolium ambiguum(Rhizobium leguminosarumsv.trifolii). Lateral gene transfer of specific symbiosis genes within rhizobial genera is an important mechanism allowing legumes to form symbioses with rhizobia adapted to particular soils. Strain-specific legume rhizobia symbioses can develop in particular habitats.
authors.affiliation: Faculty of Agriculture and Life Sciences, Lincoln University, PO Box 84, Lincoln 7647, New Zealand. mitchell.andrews@lincoln.ac.nz.
authors.forename: Mitchell
authors.initials: M
authors.lastname: Andrews
authors.affiliation: Faculty of Agriculture and Life Sciences, Lincoln University, PO Box 84, Lincoln 7647, New Zealand. moragandrews@gmail.com.
authors.forename: Morag E
authors.initials: ME
authors.lastname: Andrews
mesh_terms: D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics; D020369:Bradyrhizobium / Q000145:classification / Q000235:genetics / Q000502:physiology; D049921:Cupriavidus / Q000145:classification / Q000502:physiology; D007887:Fabaceae / Q000378:metabolism / Q000382:microbiology*; D010802:Phylogeny; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism; D012231:Rhizobium / Q000145:classification / Q000235:genetics / Q000502:physiology*; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S
keywords: Leguminosae; N2 fixation; lateral gene transfer; nod genes; nodulation