Six nodulation genes of nod box locus 4 in Rhizobium meliloti are involved in nodulation signal production: nodM codes for d-glucosamine synthetase

Abstract

The nucleotide sequence of the nod box locus n4 in Rhizobium meliloti was determined and revealed six genes organized in a single transcriptional unit, which are induced in response to a plant signal such as luteolin. Mutations in these genes influence the early steps of nodule development on Medicago, but have no detectable effect on Melilotus, another host for R. meliloti. Based on sequence homology, the first open reading frame (ORF) corresponds to the nodM gene and the last to the nodN gene of Rhizobium leguminosarum. The others do not exhibit similarity to any genes sequenced so far, so we designated them as nolF, nolG, nolH and nolI, respectively. We found that the n4 locus, and especially the nodM and nodN genes, are involved in the production of the root hair deformation (Had) factor. NodM exhibits homology to amidotransferases, primarily to the D-glucosamine synthetase encoded by the glmS gene of Escherichia coli. We demonstrated that in E. coli the regulatory gene nodD together with luteolin can activate nod genes. On this basis we showed that nodM complemented an E. coli glmS- mutation, indicating that nodM can be considered as a glmS gene under plant signal control. Moreover, exogenously supplied D-glucosamine restored nodulation of Medicago by nodM mutants. Our data suggest that in addition to the housekeeping glmS gene of R. melioti, nodM as a second glmS copy provides glucosamine in sufficient amounts for the synthesis of the Had factor.

Nucleotide sequence and predicted functions of the entire Sinorhizobium meliloti pSymA megaplasmid

“…The nodM nod box regulatory sequence presumably controls expression of an operon that was previously reported to consist of six genes (nodM nolFGHI nodN; ref. 34). Our analysis indicates that the previously described NolG, NolH, and NolI instead encode a single 1,065-aa protein, NolG, which shares global homology with proteins such as EnvD, CnrA, and CzcA (35).…”

Rhizobium nodM and nodN genes are common nod genes: nodM encodes functions for efficiency of nod signal production and bacteroid maturation

“…It was proposed that nodM controls cultivar specificity, possibly by modifying the host specificity of the signal molecules. This suggestion seemed to contradict reports that nodM is a glucosamine synthase gene under plant signal control (1,21). Therefore, we set out to identify various possible functions ofnodM ex planta or in planta and to investigate whether these functions are involved in determining host specificity.…”

“…The nodulation gene products are involved in producing signal molecules, the Nod factors, which elicit curling and deformation of the root hairs and meristematic cell division, leading to nodule formation (12). Using R meliloti strains overproducing the Nod factors, certain plant hosts (1,32), while in other hosts, nodM was required for efficient nodulation (1). Moreover, in R. leguminosarum bv.…”

Structural and functional aspects of the multidrug efflux pump AcrB

“…In prokaryotes, their main physiological function seems to be associated with the extrusion of noxious substrates, with notable exceptions such as the secretory accessory proteins SecDF (Gardel et al, 1987;Pogliano and Beckwith, 1994), lipid exporter MmpL7 (Camacho et al, 2001;Domenech et al, 2005) and the putative lipooligosaccharide nodulation factor exporter NolG (Baev et al, 1991). In Eukarya, however, the functionally characterized RND proteins seem to be involved in lipid homeostasis Sleat et al, 2004;Infante et al, 2008a,b) and cell morphogenesis (Taipale et al, 2002;Nakano et al, 2004).…”