Lipopolysaccharide mutants of Rhizobium meliloti are not defective in symbiosis

Clover, Ralph; Kieber, Joseph J.; Signer, Ethan R.

doi:10.1128/jb.171.7.3961-3967.1989

Cited by 49 publications

(45 citation statements)

References 48 publications

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“…It is perhaps not surprising that exoB is not regulated by exoR and exoS because exoB mutants are also defective for the production of a second exopolysaccharide, EPS II (13,41), and show lipopolysaccharide alterations (4,18). Recently it has been shown that the exoB gene encodes UDP-galactose epimerase, which converts UDP-glucose to UDP-galactose (3a olism [1], and therefore exoB mutants are not galactose sensitive.)…”

Section: Resultsmentioning

confidence: 99%

Regulation of Rhizobium meliloti exo genes in free-living cells and in planta examined by using TnphoA fusions

1991

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The exo loci of Rhizobium meliloti are necessary for the production of an acidic exopolysaccharide, EPS I, that is needed for alfalfa nodule invasion by strain RmlO21. We have isolated and characterized alkaline phosphatase fusions made with TnphoA in several exo loci of R. meliloti and used these fusions to examine the subcellular localization of exo gene products and the regulation of exo genes in free-living cells and in planta. In the course of this work, we isolated a new exo locus, exoT. We have obtained evidence that several of the exo loci may encode membrane proteins. The activity of TnphoA fusions in several exo loci is increased two-to fivefold in the presence of the regulatory mutations exoR95 and exoS96. While examining the regulation of the exo genes by exoR95 and exoS96, we found that certain classes of exo mutations are lethal in an exoR95 or exoS96 background unless a plasmid complementing the exo mutation is present. This result has possible implications for the role of these exo loci in EPS I biosynthesis. We have developed a method for staining nodules specifically for the alkaline phosphatase activity present in the inducing bacteria and used this method to show that an exoF::TnphoA fusion is expressed mainly in the invasion zone of the nodule.

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Section: Resultsmentioning

confidence: 99%

Regulation of Rhizobium meliloti exo genes in free-living cells and in planta examined by using TnphoA fusions

1991

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“…Although R. meliloti that are deficient in LPS induce Ng-fixing nodules on alfalfa (Clover, Kieber & Signer, 1989), Ips mutants of R. leguminosarum bv. viciae elicit nodules on pea or vetch, which, while appearing to be normal overall, are Fix because the rhizobia are not released from the infection threads (Priefer, 1989;Brewin et al, 1990).…”

Section: Infectionmentioning

confidence: 99%

Developmental biology of legume nodulation

1992

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SUMMARY Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non‐legume hosts, such as rice or maize, increase in number and scope.

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“…a genus of gram-negative soil bacteria, have been described that are unable to penetrate the root hair cells of RAETZ legumes (116,117). In some of these mutants there are alterations in the composition of O-antigen (116).…”

Section: Biochemistry Of O-antigensmentioning

confidence: 99%