title: Failure to fix nitrogen by non-reproductive symbiotic rhizobia triggers host sanctions that reduce fitness of their reproductive clonemates.
abstract: The legume-rhizobia symbiosis is a classical mutualism where fixed carbon and nitrogen are exchanged between the species. Nonetheless, the plant carbon that fuels nitrogen (N(2)) fixation could be diverted to rhizobial reproduction by 'cheaters'--rhizobial strains that fix less N(2) but potentially gain the benefit of fixation by other rhizobia. Host sanctions can decrease the relative fitness of less-beneficial reproductive bacteroids and prevent cheaters from breaking down the mutualism. However, in certain legume species, only undifferentiated rhizobia reproduce, while only terminally differentiated rhizobial bacteroids fix nitrogen. Sanctions were, therefore, tested in two legume species that host non-reproductive bacteroids. We demonstrate that even legume species that host non-reproductive bacteroids, specifically pea and alfalfa, can severely sanction undifferentiated rhizobia when bacteroids within the same nodule fail to fix N(2). Hence, host sanctions by a diverse set of legumes play a role in maintaining N(2) fixation.
authors.affiliation: Department of Plant Biological Sciences, University of Minnesota, 250 Biological Sciences, 1445 Gortner Avenue, Saint Paul, MN 55108, USA. oonox001@umn.edu
authors.forename: Ryoko
authors.initials: R
authors.lastname: Oono
authors.forename: Carolyn G
authors.initials: CG
authors.lastname: Anderson
authors.forename: R Ford
authors.initials: RF
authors.lastname: Denison
mesh_terms: D000455:Medicago sativa / Q000378:metabolism / Q000382:microbiology*; D009586:Nitrogen Fixation; D018532:Pisum sativum / Q000378:metabolism / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D013559:Symbiosis