title: Peribacteroid space acidification: a marker of mature bacteroid functioning in Medicago truncatula nodules.
abstract: Legumes form a symbiotic interaction with Rhizobiaceae bacteria, which differentiate into nitrogen-fixing bacteroids within nodules. Here, we investigated in vivo the pH of the peribacteroid space (PBS) surrounding the bacteroid and pH variation throughout symbiosis. In vivo confocal microscopy investigations, using acidotropic probes, demonstrated the acidic state of the PBS. In planta analysis of nodule senescence induced by distinct biological processes drastically increased PBS pH in the N2 -fixing zone (zone III). Therefore, the PBS acidification observed in mature bacteroids can be considered as a marker of bacteroid N2 fixation. Using a pH-sensitive ratiometric probe, PBS pH was measured in vivo during the whole symbiotic process. We showed a progressive acidification of the PBS from the bacteroid release up to the onset of N2 fixation. Genetic and pharmacological approaches were conducted and led to disruption of the PBS acidification. Altogether, our findings shed light on the role of PBS pH of mature bacteroids in nodule functioning, providing new tools to monitor in vivo bacteroid physiology.
authors.affiliation: UMR INRA 1355-CNRS 7254-Université de Nice Sophia-Antipolis, Institut Sophia Agrobiotech, 400 route des Chappes, F-06903, Sophia Antipolis, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Pierre
authors.forename: Gilbert
authors.initials: G
authors.lastname: Engler
authors.forename: Julie
authors.initials: J
authors.lastname: Hopkins
authors.forename: Frédéric
authors.initials: F
authors.lastname: Brau
authors.forename: Eric
authors.initials: E
authors.lastname: Boncompagni
authors.forename: Didier
authors.initials: D
authors.lastname: Hérouart
mesh_terms: D003624:Darkness; D006863:Hydrogen-Ion Concentration; D046913:Medicago truncatula / Q000201:enzymology / Q000382:microbiology*; D009586:Nitrogen Fixation; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012231:Rhizobium / Q000502:physiology*; D053204:Root Nodules, Plant / Q000382:microbiology*; D013312:Stress, Physiological; D013559:Symbiosis
chemical_list: D006180:Proton-Translocating ATPases
keywords: Sinorhizobium meliloti; acidic compartment; confocal microscopy; nitrogen-fixing symbiosis; ratio imaging