The Rhizobium meliloti region located downstream of the nod box n6 is involved in the specific nodulation of Medicago lupulina |
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Authors: | Claire Plazanet Guislaine Réfrégier Nathalie Demont Georges Truchet Charles Rosenberg |
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Institution: | Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS-INRA, B.P. 27, 31326 Castanel-Tolosan Cedex, France; Laboratoire de Pharmacologie et Toxicologie Fondamentales, CNRS, 205 route de Narbonne, 31077 Toulouse Cedex, France |
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Abstract: | Abstract Six nod box regulatory sequences are present in the Rhizobium meliloti genome. We have analysed the DNA region located downstream of nod box n6, and identified three open reading frames, designated nolQa, nolQb and nolS . LacZ fusions in these ORFs are not induced by classical nod gene inducers, which indicates that their expression either is not under the control of the nod box, or involves another regulatory mechanism acting in conjunction with the NodD/nod box regulatory circuit. Mutations in this n6 locus result in a delay in nodule formation on a particular host, Medicago lupulina . As this region is not strictly conserved among different R. meliloti strains, nolQa, nolQb and nolS may constitute auxiliary nodulation genes, for which the selection pressure is limited to particular host plants. |
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Keywords: | Rhizobium meliloti Nodulation gene nod box Medicago lupulina |
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