Isolation and characterization of symbiotic mutants of bradyrhizobium sp. (Arachis) strain NC92: mutants with host-specific defects in nodulation and nitrogen fixation

Wilson, Kerry‐Jayne; Anjaiah, V.; Nambiar, P. T. C.; Ausubel, Frederick M.

doi:10.1128/jb.169.5.2177-2186.1987

Cited by 29 publications

(19 citation statements)

References 61 publications

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“…Some recent studies using broad host range rhizobia have examined the response of several host species to individual bacterial mutants. Wilson et al (1987) used mutants of Bradyrhizohium sp. {Arachis) strain NC 92 and studied their ability to nodulate and fix nitrogen with Arachis (wound infection) as well as Macroptilium atropurpureum and Cafanus cajan, which are nodulated by the wild-type strain via hair infection (both hosts are in the same legume tribe as soybean).…”

Section: Infection {Inf)mentioning

confidence: 99%

Which steps are essential for the formation of functional legume nodules?

Sprent

1989

New Phytologist

101

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summary Nodulation is reviewed in terms of the phenotypes proposed by Vincent (1980). Individual legumes may be infectible by one or more of the three bacterial genera (collectively known as rhizobia) Rhizobium, Bradyrhizobium, or Azorhizobium. The type of infection process by which rhizobia gain entry is largely governed by the host genotype. In addition to the widely studied root‐hair pathway, infections may be associated with lateral root emergence or occur between root epidermal cells. The exact chemical and physical nature of the root hair/epidermal cell wall is likely to be a critical factor in determining whether infections can proceed. In addition to differing with species, wall composition may be influenced by soil chemical (e.g. Ca2+) and biotic factors (e.g. bacteria). Rhizobial features essential for infection include particular surface polysaccharides and the induction of nodulation genes by plant root exudates. Neither of these is likely to be a major barrier to the extension of nodulation to new hosts. Dissemination of rhizobia within developing nodules may be intercellular, via infection threads or by division of a small number of infected cells. All functional symbioses eventually have ‘intracellular’ bacteria, in the sense that rhizobia are geographically located within the boundary of the host cell walls. However, they remain extracellular in the sense that they are always confined by a membrane which is largely of host cell origin. In some genera they are also surrounded by infection thread walls, probably modified forms of ‘invasive’ infection thread walls, which allow differentiation of rhizobia into the nitrogen‐fixing form. Thus, natural, functional, symbioses may (a) never involve a stage in which bacteria are confined within tubular infection threads or (b) never release bacteria from infection threads. These features are determined by host genotype. The one feature of legume nodules so far found never to vary is the stem‐like character of a peripheral vascular system. This contrasts with the central vascular system of actinorhizas and the rhizobial‐induced nodules on the Ulmaceous genus Parasponia. Although of great intrinsic interest, this character is unlikely to present an insurmountable barrier to the extension of nodulation to new species. Other features, such as the ability to produce haemoglobin are now known to the in the genetic makeup of many higher plants. The discovery of the wide range of nodule structures occurring in nature, together with work on mutant rhizobia which may bypass critical stages in the nodulation process, suggest various ways in which the extension of nodulation to non‐nodulated legumes and to other (initially at least, dicotyledonous) plants may be engineered.

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Section: Infection {Inf)mentioning

confidence: 99%

Which steps are essential for the formation of functional legume nodules?

Sprent

1989

New Phytologist

101

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“…In R. meliloti, Rhizobium leguminosarum bv. viciae, and B. japonicum, C4-dicarboxylate transport mutants formed ineffective (Fix-) nodules (6,30,41) that have been reported, nitrogen fixation ability is significantly reduced compared with that of the wild type but not completely blocked (11,15,29,52,60,62). These results suggest that the host-specific failure is due to some postinfection breakdown in the interaction between plant and bacterium and is not directly related to the nitrogen fixation enzymatic machinery.…”

Section: Resultsmentioning

confidence: 50%

“…For this reason, we chose to name ORFA hsfA (for host-specific fixation). DISCUSSION Host-specific fixation mutants of several Rhizobium and Bradyrhizobium strains have been reported (10,29,52,60,62). However, these earlier reports failed to identify the specific gene(s) responsible for the host-specific fixation phenotype.…”

Section: Resultsmentioning

confidence: 69%

“…A mutant of Bradyrhizobium sp. (Arachis) strain NC92 which formed an ineffective symbiosis with pigeonpea but effective symbioses with groundnut and siratro was isolated (62). Recent physiological experiments with this mutant indicate that the defect appears to lie in the ability of each of the host plants to tolerate or support nodulation by the mutant and appears not to be due to a specific interaction between the mutant and a particular host plant.…”

mentioning

confidence: 99%

“…Mutants of rhizobia which have lost the ability to fix nitrogen with some, but not all, of their normal legume hosts have been isolated (10,14,29,52,60,62). Tn5-induced mutants of Rhizobium strain NGR234" with altered exopolysaccharide production produce Fix' nodules on some of their hosts but t Present address: Department of Nutritional Science, University of California-Berkeley, Berkeley, CA 94720.…”

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confidence: 99%

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Identification and characterization of a novel Bradyrhizobium japonicum gene involved in host-specific nitrogen fixation

et al. 1994

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To understand the genetic mechanism of host specificity in the interaction between rhizobia and their hosts, it is important to identify genes that influence both early and late steps in symbiotic development. This paper focuses on the little-understood genetics of host-specific nitrogen fixation. A deletion mutant ofBradyrhizobium japonicum, strain NAD163, was found to induce effective, nitrogen-fixing nodules on soybean and siratro plants but produced ineffective nodules on cowpea plants. Additional transposon and deletion mutants defined a small region that conferred this phenotype, and this region was sequenced to identify two putative open reading frames (ORFs). Data indicate that only one of these ORFs is detectable in bacteroids. This ORF was termed hsfA, with a predicted protein product of 11 kDa. The transcriptional start site of hsfA was determined and found to coincide with a predicted RpoN-dependent promoter. Microscopic studies of nodules induced by the wild type and hsfA mutants on cowpea and soybean plants indicate that the cowpea mutant nodules are slow to develop. The data indicate that hsfA appears to play a crucial role in bacteroid development on cowpea but does not appear to be essential for nitrogen fixation on the other hosts tested.It is well-known that specific strains of rhizobia enter into nitrogen-fixing symbioses with specific hosts. A number of host-specific genetic determinants that affect the early steps of symbiosis, infection, and nodulation (e.g., root hair curling and cortical cell division; see references 3, 21, and 31) have been studied. However, less is known about host-specific events that affect later steps in the development and maintenance of the symbiosis.Bacterial host specificity in symbiotic nitrogen fixation has been suggested by the observation that some wild-type Rhizobium strains form effective (Nod' Fix') nodules on some legumes but form ineffective (Nod' Fix-) nodules on other hosts (e.g., see references 9, 16, 37, and 55

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