title: Growth conditions determine the DNF2 requirement for symbiosis.
abstract: Rhizobia and legumes are able to interact in a symbiotic way leading to the development of root nodules. Within nodules, rhizobia fix nitrogen for the benefit of the plant. These interactions are efficient because spectacularly high densities of nitrogen fixing rhizobia are maintained in the plant cells. DNF2, a Medicago truncatula gene has been described as required for nitrogen fixation, bacteroid's persistence and to prevent defense-like reactions in the nodules. This manuscript shows that a Rhizobium mutant unable to differentiate is not sufficient to trigger defense-like reactions in this organ. Furthermore, we show that the requirement of DNF2 for effective symbiosis can be overcome by permissive growth conditions. The dnf2 knockout mutants grown in vitro on agarose or Phytagel as gelling agents are able to produce nodules fixing nitrogen with the same efficiency as the wild-type. However, when agarose medium is supplemented with the plant defense elicitor ulvan, the dnf2 mutant recovers the fix- phenotype. Together, our data show that plant growth conditions impact the gene requirement for symbiotic nitrogen fixation and suggest that they influence the symbiotic suppression of defense reactions in nodules.
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Fathi
authors.initials: F
authors.lastname: Berrabah
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Bourcy
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Cayrel
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Alexis
authors.initials: A
authors.lastname: Eschstruth
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Mondy
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Ratet
authors.affiliation: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif sur Yvette, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gourion
mesh_terms: D055786:Gene Knockout Techniques; D046913:Medicago truncatula / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism / Q000382:microbiology*; D009154:Mutation; D009586:Nitrogen Fixation / Q000187:drug effects; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011134:Polysaccharides / Q000494:pharmacology; D012231:Rhizobium / Q000502:physiology; D013559:Symbiosis / Q000187:drug effects
chemical_list: D010940:Plant Proteins; D011134:Polysaccharides; C571831:ulvan