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

Abstract

Earlier, we showed that Rhizobium meliloi nod&f codes for glucosamine synthase and that nodM and nodN mutants produce strongly reduced root hair deformation activity and display delayed nodulation of Medicago sativa (Baev et al., Mol. Gen. Genet. 228:113-124, 1991). Here, we demonstrate that nodPf and nodN genes from Rhizobium leguminosarum biovar viciae restore the root hair deformation activity of exudates of the corresponding R. meliloti mutant strains. Partial restoration of the nodulation phenotypes of these two strains was also observed. In nodulation assays, galactosamine and N-acetylglucosamine could substitute for glucosamine in the suppression of the R. melilot nodM mutation, although N-acetylglucosamine was less efficient. We observed that in nodules induced by nodM mutants, the bacteroids did not show complete development or were deteriorated, resulting in decreased nitrogen fixation and, consequently, lower dry weights of the plants. This mutant phenotype could also be suppressed by exogenously supplied glucosamine, N-acetylglucosamine, and galactosamine and to a lesser extent by glucosamine-6-phosphate, indicating that the nodAf mutant bacteroids are limited for glucosamine. In addition, by using derivatives of the wild type and a nod&t mutant in which the nod genes are expressed at a high constitutive level, it was shown that the nodM mutant produces significantly fewer Nod factors than the wild-type strain but that their chemical structures are unchanged. However, the relative amounts of analogs of the cognate Nod signals were elevated, and this may explain the observed host range effects of the nodM mutation. Our data indicate that both the nod&f and nodN genes of the two species have common functions and confirm that NodM is a glucosamine synthase with the biochemical role of providing sufficient amounts of the sugar moiety for the synthesis of the glucosamine oligosaccharide signal molecules.Rhizobia are capable of establishing symbiotic associations with their legume hosts. During this process, the bacteria undergo rapid developmental changes in order to make the transition from a soil environment through the root surface environment to a new ecological niche inside the plant host cells. The partnership between a given plant host and its microsymbiont is highly specific; most leguminous plants can be nodulated by a more or less limited number of Rhizobium species. For example, Rhizobium meliloti nodulates species of the genera Medicago, Meliotus, and Trigonella (11).Numerous bacterial and plant genes are expressed specifically during nodule development (19 Lerouge and coworkers (17) identified a major alfalfa-specific signal molecule as an acylated and sulfated glucosamine tetrasaccharide. Using a similar approach, we showed that R meliloti produces a family of biologically active Nod signal molecules (26). Host-specific signal molecules secreted by Rhizobium leguminosarum have also been identified (30).In different rhizobia, common and host-specific nod genes have been identified (12). The b...

Genomic basis of broad host range and environmental adaptability of Rhizobium tropici CIAT 899 and Rhizobium sp. PRF 81 which are used in inoculants for common bean (Phaseolus vulgaris L.)

“…also harbor paralogous glucosamine synthases. NodM is required for efficient nodulation of some hosts [63]. …”

The Hotdog fold: wrapping up a superfamily of thioesterases and dehydratases

“…We also include a NodN-like sub-subfamily here that is found in another cluster containing several other MaoC proteins. Rhizobium and related species form nodules on the roots of their legume hosts, a symbiotic process that requires production of Nod factors, which are signal molecules involved in root hair deformation and meristematic cell division [26]. The nodulation gene products, including NodN, are involved in producing the Nod factors, however the role played by NodN is unclear.…”

Genetic Organization and Transcriptional Regulation of Rhizobial Nodulation Genes

“…Putative nodulation genes only known from hybridization or partial sequence data are indicated tentatively by broken 01., 1995;Baev et al, 1991Baev et al, ,1992Baev and Kondorosi,1992;Barlier, 1995;Barnett and Long,1990;Cervantes et 01., 1989; Van Rhijn, 1994; B. japonicum: Chun et 01., 1994;Deshmane and Stacey, 1989;Dockendorff et 01., 1994a.,b;GOttfert et 01., 1989GOttfert et 01., , 1990aGOttfert et 01., .,b, 1992 (Cloutier st 01., 1996a,b), Bradyrhizobium elkanii (Dobert et 01., 1994), Bradyrhizobium sp. (Parasponia) (Scott, 1986) snd Bradyrhizobium (Arachis) sp.…”

“…Ammonia repression of nodulation genes is, however, not general in rhizobia since neither nodD nor nodABC genes of R. leguminosarum bv. viciae are regulated in response to combined nitrogen (Baev and Kondorosi, 1992).…”