Host Recognition in the <i>Rhizobium</i>-Soybean Symbiosis

Halverson, Larry J.; Stacey, Gary

doi:10.1104/pp.74.1.84

Cited by 50 publications

(31 citation statements)

References 17 publications

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“…It appears that the nodE mutant strain of R. leguminosarum may be unable to capitalize on the initial period of infectibility but could subsequently induce infection, thus showing a delayed nodulation phenotype. A mutant of R. japonicum with a similar phenotype has been described previously (10), and it was shown that with this strain the delayed initiation of nodulation could be reversed by the addition of root exudate from soybean seedlings. Interestingly, it appears that the phenotype of the nodE mutant strain described here could be at least partially reversed if the seedlings were grown initially in the absence of light.…”

Section: Resultsmentioning

confidence: 99%

Nodulation inhibition by Rhizobium leguminosarum multicopy nodABC genes and analysis of early stages of plant infection

Knight¹,

Rossen²,

Robertson³

et al. 1986

J Bacteriol

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During analysis of early events in the infection and nodulation of Vicia hirsuta roots inoculated with normal and mutant strains of Rhizobium leguminosarum and strains containing cloned nodulation (nod) The morphological steps involved in the nodulation of leguminous plants by Rhizobium spp. have been clearly described. In general, the initial step involves a characteristic curling of the root hair, followed by an invagination of the root hair cell wall. This invagination develops into an infection thread which grows through and between root hair cells until it finally enters meristematic cells. At this point, bacteria that have grown along the infection thread are budded off and surrounded by a membrane (the peribacteroid membrane) of plant origin (14,15,18).Previously, we identified a series of transposon-(Tn5) induced mutants of R. leguminosarum (7) which were affected in their ability to nodulate Pisum sativum (peas). The mutations were all located within a 10-kilobase-pair (kb) region of DNA which had been shown to contain nodulation and host range genes (6,8). Five different classes of mutants were identified on the basis of the phenotypes of the mutant strains and on the locations of the TnS inserts (7). These observations, taken together with DNA sequence data from this part of the nod region (16; C. A. Shearman, L. Rossen, A. W. B. Johnston, and J. A. Downie, submitted for publication), allowed six different nod genes (called nodA, nodB, nodC, nodD, nodE, and nodF) to be identified (Fig. 1) required for root hair curling, and mutations within these genes blocked nodulation; nodD mutant were Nod-but did induce a delayed root hair curling and deformation response; nodE and class V mutations (e.g., nodE68::TnS) caused a delay in nodulation and induced root hair curlingdeformation (7).Only the nodABC genes are essential for root hair curling and deformation because a strain cured of its symbiotic plasmid but containing the subcloned nodABC genes could induce root hair curling and deformation (16) Table 1; media and general growth conditions were those described by Beringer (2). For inoculation of plants, Rhizobium cultures were grown for 2 days on agar slants containing 10 ml of medium, the bacteria were suspended in 4 ml of water, and 0.1 ml was added to the plant roots (this corresponds to about 5 x 107 bacteria). Bacteria were isolated from surface-sterilized nodules as described previously (3).Growth of plants and analysis of nodulation. Peas (variety Wisconsin Perfection) were surface sterilized and grown in 200 ml of sterile agar plant medium as described previously (3). V. hirsuta seeds were treated with concentrated H2SO4 for 20 min, rinsed three times in sterile water, and then left 552

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Section: Resultsmentioning

confidence: 99%

Nodulation inhibition by Rhizobium leguminosarum multicopy nodABC genes and analysis of early stages of plant infection

Knight¹,

Rossen²,

Robertson³

et al. 1986

J Bacteriol

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“…In addition, observations were restricted to the region of the root containing cells competent to be infected, i.e. the zone of no and emerging root hairs (4,6,19 (2,3,14). The effect of these solutions on nodulation is thought to reflect changes in the behavior of rhizobia before infection, and thus it was of interest to determine if culture of rhizobia in similar solutions enhanced bacterial adsorption.…”

Section: Resultsmentioning

confidence: 99%

Adsorption of Slow- and Fast-Growing Rhizobia to Soybean and Cowpea Roots

Pueppke

1984

Plant Physiol.

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cowpea, where the adsorption of strain 102F51 was similar to that of strain 3G4bI6. The initial adsorption rates of bacteria cultured in synthetic media and in the presence of soybean roots were about the same. Addition of soybean lectin to the bacterial inoculum failed to influence initial adsorption rates. Both treatments, however, reduced the numbers of bacteria that bound after incubation with roots for 120 minutes. The relationship between the logarithm of the number of strain 138 cells bound per soybean root segment and the logarithm of the density of bacteria in the inoculum was linear over filve orders of magnitude. Binding of strain 138 to soybean roots was greatest at room temperature (27°C) and substantially attenuated at both 4 and 37°C. Although R. lupini 96B9 strongly rejected a model hydrophobic plastic surface, there were no simple correlations between bacterial binding to model hydrophobic and hydrophilic plastic surfaces and bacterial adsorption to roots.

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“…For delayed-nodulation assays and comparison of nodulation ability on different soybean cultivars (i.e., Glycine max cv. Essex, Harosoy, Williams, Forest, and Peking), seedlings were sprouted as before and then grown three to a pack in clear plastic pouches (Dispo Seed Pack; Northrup King Seed Co.) as described previously (24).…”

Section: Methodsmentioning

confidence: 99%

nodZ, a unique host-specific nodulation gene, is involved in the fucosylation of the lipooligosaccharide nodulation signal of Bradyrhizobium japonicum

et al. 1994

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The nodulation genes of rhizobia are regulated by the nodD gene product in response to host-produced flavonoids and appear to encode enzymes involved in the production of a lipo-chitose signal molecule required for infection and nodule formation. We have identified the nodZ gene of Bradyrhizobium japon&um, whose product is required for the addition of a 2-0-methylfucose residue to the terminal reducing N-acetylglucosamine of the nodulation signal. This substitution is essential for the biological activity of this molecule. Mutations in nodZ result in defective nodulation of siratro. Surprisingly, although nodZ clearly codes for nodulation function, it is not regulated by NodD and, indeed, shows elevated expression in planta. Therefore, nodZ represents a unique nodulation gene that is not under the control of NodD and yet is essential for the synthesis of an active nodulation signal.Leguminous plants are infected (nodulated) by the gramnegative, soil bacteria Rhizobium, Azorhizobium, and Bradyrhizobium species, which establish a nitrogen-fixing symbiosis within the roots. There is now considerable information available concerning the genetic traits of these bacteria that are required for the establishment of nitrogen-fixing symbiosis. A number of nodulation (nod, nol) genes have been identified (48). These genes fall into two general groups: the common nod genes (e.g., nodABC) that are essential for nodulation of any host and the host specificity genes that appear to determine specific nodulation of a narrow range of hosts (reviewed in references 13, 14, and 21). Recent evidence indicates that the function of many, if not all, of the nod genes is to synthesize or modify lipooligosaccharide signal molecules that initiate many of the initial nodulation responses in the plant (13, 14, 55). For example, Rhizobium meliloti has been shown to synthesize a sulfated lipooligosaccharide that induces many of the early events of nodulation when applied to alfalfa roots (13,14). Recent results indicate that the protein products of the host specificity genes of R. meliloti, nodHPQ, are involved in the specific sulfation reaction leading to the synthesis of NodRm-1 (e.g., see references 4, 41, and 50). We recently identified the lipooligosaccharide nodulation signals produced by Bradyrhizobium japonicum USDA110 and USDA135 and Bradyrhizobium elkanii USDA61 (9,47 NodD (6,25,33

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Host Recognition in the Rhizobium-Soybean Symbiosis

Cited by 50 publications

References 17 publications

Nodulation inhibition by Rhizobium leguminosarum multicopy nodABC genes and analysis of early stages of plant infection

Nodulation inhibition by Rhizobium leguminosarum multicopy nodABC genes and analysis of early stages of plant infection

Adsorption of Slow- and Fast-Growing Rhizobia to Soybean and Cowpea Roots

nodZ, a unique host-specific nodulation gene, is involved in the fucosylation of the lipooligosaccharide nodulation signal of Bradyrhizobium japonicum

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