Identification and characterization of a Rhizobium leguminosarum bv. phaseoli gene that is important for nodulation competitiveness and shows structural homology to a Rhizobium fredii host-inducible gene.
DNA sequence analysis of a 1.4-kb SalI-HindIII segment located approximately 2 kb upstream of the Rhizobium leguminosarum bv. phaseoli syrM gene revealed the presence of an open reading frame (ORF3) encoding a putative 295-amino acid polypeptide with a molecular mass of 33,401 Da. ORF3 is homologous to a R. fredii host-inducible gene. The proteins encoded by R. l. bv. phaseoli ORF3 and by the R. fredii host-inducible gene share 37% sequence identity. In contrast to the R. fredii host-inducible gene, expression of ORF3 is not induced in the presence of Phaseolus vulgaris root exudates or by specific flavonoids, able to induce nodulation genes in R. l. bv. phaseoli. A R. l. bv. phaseoli ORF3 mutant was constructed by site-directed deletion/replacement mutagenesis. This mutant strain is not affected in symbiotic nitrogen fixation but exhibits a delay in nodulation on Phaseolus vulgaris. Moreover, this mutant was shown to be defective in competition for nodulation.
Michiels
J
J
F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Heverlee, Belgium.
Pelemans
H
H
Vlassak
K
K
Verreth
C
C
Vanderleyden
J
J
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D004269:DNA, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D012231:Rhizobium / Q000235:genetics*; D016961:Rhizobium leguminosarum / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
C095401:33.4-kDa protein, Rhizobium; D001426:Bacterial Proteins; D004269:DNA, Bacterial