Regulation of the expression of the nod box-independent nodulation gene, nolX, in Sinorhizobium fredii, a nitrogen-fixing symbiont of legume plants

Abstract nolX, a nod box-independent nodulation gene from the nitrogen-fixing symbiont, Sinorhizobium fredii, regulates cultivar-specific nodulation of soybean. Expression of this gene is triggered by isoflavonoid cues from host roots but is not mediated by a typical cis-acting nod box promoter. We...

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Bibliographic Details
Published in:FEMS microbiology letters 1997-12, Vol.157 (1), p.13-18
Main Authors: Bellato, C.M. (Missouri Univ., Columbia, MO (USA). Dept. of Plant Pathology), Pueppke, S.G, Krishnan, H.B
Format: Article
Language:English
Subjects:
BACTERIA FIJADORA DEL NITROGENO
BACTERIE FIXATRICE DE L'AZOTE
Carbon sources
Cultivars
Daidzein
EXPRESION GENICA
EXPRESSION DES GENES
FORMATION DE NODOSITES
Galactose
GENE EXPRESSION
Gene fusion
GLYCINE MAX
Homology
Inositol
Isoflavonoids
LacZ gene
Legumes
Mannitol
Methionine
Microbiology
Nitrogen fixation
NITROGEN FIXING BACTERIA
NODULACION
Nodulation
Nodulation gene
nolX
Nutritional status
Rhamnose
RHIZOBIACEAE
Rhizobium‐legume symbiosis
ROOT NODULATION
Sinorhizobium fredii
Soybeans
Xanthomonas campestris
Xylose
Yeasts
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Summary:Abstract nolX, a nod box-independent nodulation gene from the nitrogen-fixing symbiont, Sinorhizobium fredii, regulates cultivar-specific nodulation of soybean. Expression of this gene is triggered by isoflavonoid cues from host roots but is not mediated by a typical cis-acting nod box promoter. We have found that two isoflavonoids, daidzein and coumestrol, induce expression of a nolX-lacZ gene fusion at pH values between 5.5 and 8.5, with an optimum at 6.5. Expression of nolX is highly dependent on nutritional status but insensitive to salinity. Methionine and casamino acids, amendments that enhance expression of hrpF, a homologous gene from the plant pathogen Xanthomonas campestris biovar vesicatoria, have no and strongly negative effects, respectively, on expression of nolX. Growth of S. fredii on rhamnose, galactose, xylose, or myo-inositol as carbon source greatly elevates inducibility in comparison to a standard yeast extract-mannitol medium. None of the tested variables, however, released nolX from its dependence on isoflavonoids as inducers.
ISSN:0378-1097
1574-6968
DOI:10.1111/j.1574-6968.1997.tb12746.x