Expression of the Bradyrhizobium japonicum Nola Gene in Response to Chemically Distinct Soybean Inducers

Loh, John T.; Cassini, Sérvio Túlio Alves; Oliveira, Fernando F.; Stacey, Gary

doi:10.1007/0-306-47615-0_132

Cited by 8 publications

(13 citation statements)

References 2 publications

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“…In B. japonicum, repression of nod gene expression by NolA is probably an indirect effect mediated perhaps by nodD2. B. japonicum nolA, and R. meliloti nolR mutants retain the ability to nodulate their respective hosts, albeit at lower efficiency, suggesting that fine-tuning of nod gene expression is required for optimal nodulation (55). Similarly, a nodD2 mutant of NGR234 (Fig.…”

Section: Vol 182 2000 Minireview 5645mentioning

confidence: 97%

Keys to Symbiotic Harmony

2000

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At least three different sets of symbiotic signals (here, they are compared to locks and keys) are exchanged between legumes and rhizobia during nodule development. Flavonoids, the first of these, emanate from the plant and interact with rhizobial NodD proteins that serve as both environmental sensors and activators of transcription. A second set of signals is synthesized when NodD-flavonoid complexes activate transcription from nod boxes. Most of the genes immediately downstream of these promoters are involved in the synthesis of lipooligosaccharidic Nod factors that provoke deformation of root hairs and allow rhizobia to enter the root through infection threads. Fine-tuning of transcription of nodulation (nod) genes is probably related to sequence variations in individual nod boxes (there are 19 on the symbiotic plasmid of the broad-hostrange Rhizobium sp. strain NGR234). Other rhizobial products seem to be necessary for continued infection thread development, and these represent a third set of signals. Among them are extracellular polysaccharides (EPS) and related compounds, as well as proteins exported by the type three secretion system (TTSS). In the latter case, flavonoids also activate protein secretion, suggesting that the same keys can unlock different doors.Symbioses are nearly ubiquitous, and many are also persistent (56). Mutualistic, nitrogen-fixing associations between members of the plant family Leguminosae, and the soil bacteria Azorhizobium, Bradyrhizobium, Mesorhizobium, and Rhizobium (collectively called rhizobia) contribute substantially to plant productivity (111). Legume-Rhizobium symbioses are marriages between two vastly different genomes. In rhizobia, these include a chromosome plus zero to many plasmids, totalling 6 to 9 Mbp (71). In contrast, genomes of legumes are much larger, some comprising more than 20 chromosomes with total DNA contents that range from about 450 to 4,500 Mbp per haploid genome (1C) (1). As examples, the model legumes Lotus japonicus and Medicago truncatula have six or eight chromosomes totalling 450 and 500 Mbp/1C (14), respectively. Common beans (Phaseolus vulgaris) and related species (e.g., Vigna unguiculata) (both genera belong to the tribe Phaseoleae) have 11 chromosomes each (24) with DNA contents of 637 (1) and 540 Mbp/1C (50). Furthermore, several widely cultivated legumes such as Arachis hypogaea, Glycine max, and Medicago sativa are effectively polyploid, although in G. max most loci segregate as if they were diploid. Legume genomes are thus at least 50 times larger than those of their microsymbionts. Given this disparity, it is difficult to imagine that theirs is a marriage of equals. Nevertheless, their respective contributions are probably not vastly different (see reference 48). LEGUME BOWERS ARE DECORATED WITH FLAVONOIDSWhich partner initiates contact? Since plants are nonmotile, it is tempting to think that courtship begins when bacteria advance into the legume rhizosphere. Yet chemotaxis and motility among rhizobia are clearly not essential for no...

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Section: Vol 182 2000 Minireview 5645mentioning

confidence: 97%

Keys to Symbiotic Harmony

2000

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“…A unique feature of the nolA gene is that it encodes for three functionally distinct proteins (i.e., NolA 1 , NolA 2 , and NolA 3 ) derived from three in-frame ATG initiation sites (47) (Fig. 2) (47).…”

Section: Nodd and Beyondmentioning

confidence: 99%

“…2) (47). It is possible that NolA 2 may function to modulate gene expression with respect to NolA 3 function.…”

Section: Nodd and Beyondmentioning

confidence: 99%

Nodulation Gene Regulation inBradyrhizobium japonicum: a Unique Integration of Global Regulatory Circuits

Loh

Stacey

2003

Appl Environ Microbiol

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100

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“…The third pathway is regulated by NolA, a member of the MerR family of regulatory proteins, and was first identified as a genotype-specific nodulation gene that was required by B. japonicum serogroup 123 strains for the nodulation of soybean genotype PI 377578 (27). NolA was shown to activate the expression of NodD2, which in turn represses nod gene expression in Bradyrhizobium (7,19).…”

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Nodulation Gene Regulation and Quorum Sensing Control Density-Dependent Suppression and Restriction of Nodulation in theBradyrhizobium japonicum-Soybean Symbiosis

Jitacksorn

Sadowsky

2008

Appl Environ Microbiol

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The nodulation of Glycine max cv. Lambert and the nodulation-restricting plant introduction (PI) genotype PI 417566 by wild-type Bradyrhizobium japonicum USDA110 is regulated in a population-density-dependent manner. Nodulation on both plant genotypes was suppressed (inhibited) when plants received a high-density inoculum (10 9 cells/ml) of strain USDA110 grown in complex medium, and more nodules were produced on plants receiving a low-cell-density inoculum (10 5 cells/ml). Since cell-free supernatants from strain USDA110 grown to high cell density in complex medium decreased the expression of an nodY-lacZ fusion, this phenomenon was attributed to bradyoxetin-induced repression of nod gene expression. Inoculation of either the permissive soybean genotype (cv. Lambert) or PI 417566 with 10 9 cells/ml of the nodD2, nolA, nodW, and nwsB mutants of USDA110 enhanced nodulation (up to 24%) relative to that seen with inoculations done with 10 5 cells/ml of the mutants or the wild-type strain, indicating that these genes are involved in population-densitydependent nodulation of soybeans. In contrast, the number of nodules produced by an nodD1 mutant on either soybean genotype was less than those seen with the wild-type strain inoculated at a low inoculum density. The nodD2 mutant outcompeted B. japonicum strain USDA123 for nodulation of G. max cv. Lambert at a high or low inoculum density, and the results of root-tip-marking and time-to-nodulate studies indicated that the nolA and nodD2 mutants nodulated this soybean genotype faster than wild-type USDA110. Taken together, the results from these studies indicate that the nodD2 mutant of B. japonicum may be useful to enhance soybean nodulation at high inoculum densities and that NodD2 is a key repressor influencing host-controlled restriction of nodulation, density-dependent suppression of nodulation, perception of bradyoxetin, and competitiveness in the soybean-B. japonicum symbiosis.Bradyrhizobium japonicum is the nitrogen-fixing, root nodule symbiont of soybeans. Results from several studies have shown that both the bacterial and host genotypes influence the symbiotic interaction of Bradyrhizobium with soybeans (32). Several soybean genotypes, including cultivars and plant introductions (PI), were shown to be differentially nodulated by specific strains or genotypes of Bradyrhizobium japonicum (4, 28). Cregan and colleagues (4, 5) and Lohrke et al. (22) identified two soybean PI genotypes, PI 377586 and PI 417566, which restricted nodulation by B. japonicum strains in serogroups 123 and 110, respectively. The results of several subsequent studies done using one or both PI genotypes indicated that host-controlled restriction of nodulation is strain and temperature dependent, determined by the root genotype, and conditioned by a single recessive host gene (22,23). Moreover, results from preliminary microscopic studies done using both PI genotypes suggested that the nodulation restriction process occurred some time after the formation of nodule primordia in incompatible h...

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Expression of the Bradyrhizobium japonicum Nola Gene in Response to Chemically Distinct Soybean Inducers

Cited by 8 publications

References 2 publications

Keys to Symbiotic Harmony

Keys to Symbiotic Harmony

Nodulation Gene Regulation inBradyrhizobium japonicum: a Unique Integration of Global Regulatory Circuits

Nodulation Gene Regulation and Quorum Sensing Control Density-Dependent Suppression and Restriction of Nodulation in theBradyrhizobium japonicum-Soybean Symbiosis

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