title: Partner choice in Medicago truncatula-Sinorhizobium symbiosis.
abstract: In nitrogen-fixing symbiosis, plant sanctions against ineffective bacteria have been demonstrated in previous studies performed on soybean and yellow bush lupin, both developing determinate nodules with Bradyrhizobium sp. strains. In this study, we focused on the widely studied symbiotic association Medicago truncatula-Sinorhizobium meliloti, which forms indeterminate nodules. Using two strains isolated from the same soil and displaying different nitrogen fixation phenotypes on the same fixed plant line, we analysed the existence of both partner choice and plant sanctions by performing split-root experiments. By measuring different parameters such as the nodule number, the nodule biomass per nodule and the number of viable rhizobia per nodule, we showed that M. truncatula is able to select rhizobia based on recognition signals, both before and after the nitrogen fixation step. However, no sanction mechanism, described as a decrease in rhizobia fitness inside the nodules, was detected. Consequently, even if partner choice seems to be widespread among legumes, sanction of non-effective rhizobia might not be universal.
authors.affiliation: IRD, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, 34398 Montpellier Cedex 5, France. c.rangin@abdn.ac.uk
authors.forename: Cécile
authors.initials: C
authors.lastname: Gubry-Rangin
authors.forename: Marjorie
authors.initials: M
authors.lastname: Garcia
authors.forename: Gilles
authors.initials: G
authors.lastname: Béna
mesh_terms: D046913:Medicago truncatula / Q000254:growth & development / Q000382:microbiology*; D009586:Nitrogen Fixation; D010641:Phenotype; D018517:Plant Roots / Q000382:microbiology*; D053204:Root Nodules, Plant / Q000378:metabolism / Q000382:microbiology; D015398:Signal Transduction; D016962:Sinorhizobium meliloti / Q000145:classification* / Q000254:growth & development* / Q000302:isolation & purification; D012988:Soil Microbiology; D013559:Symbiosis