Transcriptional organization and expression of noIXWBTUV, a locus that regulates cultivar-specific nodulation of soybean by Rhizobium fredii USDA257

Molecular Microbiology
L G KovácsS G Pueppke

Abstract

Rhizobium fredii is a nitrogen-fixing bacterial symbiont of soybean and a number of other legume species. We have studied the transcriptional organization of a Sym plasmid locus that restricts the host range of R. fredii USDA257 at both the host species and cultivar level. The genes of this host-specificity locus, noIXWBTUV, are transcribed from three promoters. Two of these, which are upstream of noIW and noIBTUV, are oriented face to face and initiate transcription at sites that are 14 bp apart. The third lies upstream from noIX. The noIW promoter is constitutive, whereas the noIB and noIX promoters are inducible by flavonoid signals. We have attempted to express genes from this locus in Escherichia coli systems, both in vivo and in vitro. We detected the insert- and orientation-specific expression of two genes, noIX and noIW, but we were unable to obtain expression of noIBTUV. Antiserum raised against NoIT nevertheless detected an abundantly expressed polypeptide of the predicted size in protein extracts of USDA257. This observation, as well as RNA dot blot data from a series of mutants, indicates that noIBTUV is expressed as a single transcriptional unit in R. fredii. Immunological detection of NoIT, and of a second protein...Continue Reading

Citations

Jul 12, 2008·Molecular Plant-microbe Interactions : MPMI·Susanne ZehnerMichael Göttfert
Dec 17, 2002·Molecular Plant-microbe Interactions : MPMI·Andrea KrauseMichael Göttfert
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