Bradyrhizobium japonicum glnB, a putative nitrogen-regulatory gene, is regulated by NtrC at tandem promoters

Abstract

The glnB gene from Bradyrhizobium japonicum, the endosymbiont of soybeans (Glycine max), was isolated and sequenced, and its expression was examined under various culture conditions and in soybean nodules. The B. japonicum glnB gene encodes a 12,237-dalton polypeptide that is highly homologous to the glnB gene products from Klebsiella pneumoniae and Escherichia coli. The gene is located directly upstream from glnA (encoding glutamine synthetase), a linkage not observed in enteric bacteria. The glnB gene from B. japonicum is expressed from tandem promoters, which are differentially regulated in response to the nitrogen status of the medium. Expression from the downstream promoter involves the B. japonicum ntrC gene product (NtrC) in both free-living and symbiotic cells. Thus, glnB, a putative nitrogen-regulatory gene in B. japonicum, is itself Ntr regulated, and NtrC is active in B. japonicum cells in their symbiotic state.

An alternative PII protein in the regulation of glutamine synthetase in Escherichia coli

“…In A. brasilense, transcription of glnB is elevated five-to sixfold by nitrogen limitation, although this expression is not NRI dependent (de Zamaroczy et al, 1993). As in A. brasilense, the glnB gene in both Bradyrhizobium japonicum (Martin et al, 1989) and in Rhodobacter capsulatus (Foster-Hartnett and Kranz, 1994) is transcribed from tandem promoters. Although NRI is involved in the expression of the glnB gene in the latter two bacteria, their glnB transcription is hardly regulated by the nitrogen status.…”

Key Role of Bacterial NH 4 + Metabolism in Rhizobium-Plant Symbiosis

“…The same gene organization is present in the genome of M. loti (82). An N-regulated promoter, activated by NtrC and located upstream of glnB, drives the generation of glnBA transcripts (29,52,109). Hence, glnB expression in R. leguminosarum is N regulated (fourfold lower in NH 4 ϩ compared to NO 3 Ϫ ), while it is constitutive in enteric bacteria (for a review, see reference 84).…”

PIISignal Transduction Proteins, Pivotal Players in Microbial Nitrogen Control

“…One gene encodes a P II protein that is very similar to E. coli GlnB and is located upstream of and cotranscribed with glnA (the structural gene for glutamine synthetase I) (7,27,41,94,113,127,151,158,262). The second gene encodes a protein similar to GlnK and is linked to an amtB homologue (125,157,182,185,222,254) (Y. Zhang and G. Roberts, personal communication).…”

“…The glnA gene is constitutively expressed from a 70 -like promoter, and although glnB is expressed from the 70 -like promoter in nitrogen sufficiency and from a 54 -dependent promoter in nitrogen limitation, there is very little variation in the amount of transcript in response to the change in nitrogen status (151).…”