title: Symbiosis within Symbiosis: Evolving Nitrogen-Fixing Legume Symbionts.
abstract: Bacterial accessory genes are genomic symbionts with an evolutionary history and future that is different from that of their hosts. Packages of accessory genes move from strain to strain and confer important adaptations, such as interaction with eukaryotes. The ability to fix nitrogen with legumes is a remarkable example of a complex trait spread by horizontal transfer of a few key symbiotic genes, converting soil bacteria into legume symbionts. Rhizobia belong to hundreds of species restricted to a dozen genera of the Alphaproteobacteria and Betaproteobacteria, suggesting infrequent successful transfer between genera but frequent successful transfer within genera. Here we review the genetic and environmental conditions and selective forces that have shaped evolution of this complex symbiotic trait.
authors.affiliation: INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, Castanet-Tolosan, France; CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, Castanet-Tolosan, France; New Zealand Institute for Advanced Study, Massey University, Auckland, New Zealand.
authors.forename: Philippe
authors.initials: P
authors.lastname: Remigi
authors.affiliation: Department of Microbiology, Nanjing Agricultural University, Nanjing, China; Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Biology, University of York, York YO10 5DD, UK.
authors.forename: J Peter W
authors.initials: JPW
authors.lastname: Young
authors.affiliation: INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, Castanet-Tolosan, France; CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, Castanet-Tolosan, France. Electronic address: catherine.masson@toulouse.inra.fr.
authors.forename: Catherine
authors.initials: C
authors.lastname: Masson-Boivin
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics / Q000502:physiology; D005075:Biological Evolution; D019143:Evolution, Molecular; D007887:Fabaceae / Q000235:genetics / Q000382:microbiology* / Q000502:physiology; D005798:Genes, Bacterial; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology*; D010802:Phylogeny; D012231:Rhizobium / Q000235:genetics / Q000502:physiology; D012988:Soil Microbiology; D013559:Symbiosis / Q000235:genetics / Q000502:physiology*
chemical_list: D009584:Nitrogen
keywords: Rhizobium; evolution; horizontal gene transfer; host adaptation; symbiosis