Rhizobium–plant signal exchange

Fisher, Robert F.; Long, Sharon R.

doi:10.1038/357655a0

Cited by 579 publications

(339 citation statements)

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“…Through a complex exchange of chemical signals, S. meliloti induces root hair curling and nodule formation on alfalfa. S. meliloti organisms trapped in the curled root hairs invade M. sativa through a tube-like structure called an infection thread and are eventually released into the cells of the developing nodule, where they differentiate into nitrogen-fixing bacteroids (8,16).…”

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confidence: 99%

Disruption of sitA Compromises Sinorhizobium meliloti for Manganese Uptake Required for Protection against Oxidative Stress

Davies

Walker

2007

J Bacteriol

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During the initial stages of symbiosis with the host plant Medicago sativa, Sinorhizobium meliloti must overcome an oxidative burst produced by the plant in order for proper symbiotic development to continue. While identifying mutants defective in symbiosis and oxidative stress defense, we isolated a mutant with a transposon insertion mutation of sitA, which encodes the periplasmic binding protein of the putative iron/ manganese ABC transporter SitABCD. Disruption of sitA causes elevated sensitivity to the reactive oxygen species hydrogen peroxide and superoxide. Disruption of sitA leads to elevated catalase activity and a severe decrease in superoxide dismutase B (SodB) activity and protein level. The decrease in SodB level strongly correlates with the superoxide sensitivity of the sitA mutant. We demonstrate that all free-living phenotypes of the sitA mutant can be rescued by the addition of exogenous manganese but not iron, a result that strongly implies that SitABCD plays an important role in manganese uptake in S. meliloti.

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confidence: 99%

Disruption of sitA Compromises Sinorhizobium meliloti for Manganese Uptake Required for Protection against Oxidative Stress

Davies

Walker

2007

J Bacteriol

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“…Nodulation is regulated by a two-way exchange of plant and bacterial signal molecules (Fisher and Long, 1992;Spaink et al, 1993). Signal exchange begins in the rhizosphere.…”

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Sugar-Binding Activity of Pea Lectin Expressed in White Clover Hairy Roots

et al. 1995

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Dénarié et al., 1992). Nodulation is regulated by a two-way exchange of plant and bacterial signal molecules (Fisher and Long, 1992;Spaink et al., 1993). Signal exchange begins in the rhizosphere. Rhizobia sense flavonoids secreted by seeds and by the host plant root, which activate the constitutively expressed nodD gene product (reviewed by Schlaman et al., 1992). This step is a determinant of host plant specificity in some Rhizobium-host plant combinations (Horvath et al., 1987; Spaink et al., 1987). Transcription of structural nod genes is under the control of NodD and results in production and secretion of specific lipochitin oligosaccharides (Nod factors), which act as host plant-specific inducers of nodule morphogenesis (reviewed by Dénarié and Cullimore, 1993;Spaink et al., 1993). Most probably, Nod factors constitute the primary determinants of host-plant specificity of nodulation.Root lectins are plant factors involved in nodulation. Lectins are nonenzymatic sugar-binding (g1yco)proteins characterized by sugar-binding specificity. For example, root PSL is Glc/Man specific (Díaz et al., 1990) and white clover root lectin is 2-deoxyglucose specific (Sherwood et al., 1984). In general, the interaction between RI uiciae and white clover does not proceed beyond root hair curling, and these bacteria are not able to penetrate host plant cells by infection thread formation (Yao and Vincent, 1969;Djordjevic et al., 1986;Huang et al., 1993). However, RI viciae is able to induce infection thread formation and nodulation in a significant percentage of white clover plants with roots transformed with the psl gene, as reported by Díaz et al. (1989Díaz et al. ( , 1995. This heterologous nodulation does not take place when a psl mutant, which encodes a non-sugar-binding protein, is used for transformation of white clover roots (Van Eijsden et al., 1992. These results strongly suggest that (a) PSL is functionally expressed in transgenic white clover roots, (b) conservation of the sugar-binding activity of PSL is necessary for infection of white clover by RI viciae, and (c) root lectin helps to break a host plant-specific barrier for nodulation. The relationship between Nod factor recognition by host plants and Rhizobium recognition by host lectin is not yet clear.PSL is an ellipsoidal, nonglycosylated dimeric lectin with two sugar-binding sites, each located near the top of two identical monomers (Einspahr et al., 1988). PSL is encoded by a single gene (Gatehouse et al., 1987;Kaminski et al., 1987) and is synthesized as a single translation product, a prolectin with a molecular mass of 28 kD. Posttranslational modifications result in a protein that dissociates into two p subunits (18 kD each) and two 01 subunits (6 kD each, Higgins et al., 1983)

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“…At present, the structure of Nod factors produced by most other rhizobia has been determmed (Fisher & Long, 1992;Spaink, 1992;Denarie & CulKmore, 1993 ;Carlson, Price & Stacey, 1995), showing that all Nod factors consist of a /?-1,4-linked ^V-acetyl-D-glucosamine backbone varying in length between three and six sugar units. The non-reducing terminal sugar moiety is substituted on the C-2 position with a fatty acid, the structure of which is variable.…”

Section: Nod Factor Structurementioning

confidence: 99%

“…NodH is homologous to sulphotransferases and was shown to have in vitro sulphotransferase activity (Schultze et al, 1995). Therefore, these enzymes are probably directly involved in catalysing the sulphation of NodRm factors (Roche et al, 1991 6;Fisher & Long, 1992;Schultze et al, 1995). R. meltloti nodRmutants have lost the ability to elicit root hair curling, infection thread formation and nodule formation on their host alfalfa, but have acquired the ability to nodulate the non-host vetch (Debelle et al, 1986;Horvath et al, 1986;Faucher et al, 1989).…”

Section: Nod Factor Structurementioning

confidence: 99%

“…In the first step, flavonoids (Table 1) excreted by the plant induce the transcription of bacterial nodulation genes (nod genes). This process involves the constitutively expressed nodD that can bind to specific flavonoids (Goethals, Van Montagu & Holsters, 1992) which turns this protein into a transcriptional activator of the other nod genes (Fisher & Long, 1992). The proteins encoded by these genes are involved in the synthesis of specific lipo-oligosaccharides (called Nod factors.…”

Section: Introdc'ctionmentioning

confidence: 99%

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Nod factor‐induced host responses and mechanisms of Nod factor perception

Heidstra

Bisseling

1996

New Phytologist

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SUMMARYSoil bacteria belonging to the genera Rhizobium, Bradyrhizobium and Azorhizobium are able to invade the roots of their leguminous host plants, where they trigger the formation of a new organ, the root nodule. At least two steps of signal exchange between the bacterium and the host plant are involved in starting the interaction. In the first step, flavonoids excreted by the plant indtjce the transcription of bacterial nodulation genes (nod genes). The itiduction of these nod genes leads tO' the .synthesis of specific lipo-oligosaccharides (called Nod factors) that can induce various root responses, e.g. root hair deformation, depolarization of the root hair membrane potential, induction of nodulin gene expression, and formation of nodule primordia.We will focus on the various nod factor-induced plant responses. We will discuss the ways these responses can be used to itiiprove our knowledge of the mechanism of Nod factor perception. Furthermore, plant genes, in particular the syni2 allele frotn .-Afghanistan pea, encoding proteins that probably are involved in Nod factor recognition, are discussed. Based on the Nod factor-induced plant responses and the phenotype displayed by sym2 peas, a model wtll be presented of how Nod factors tnay be perceived.

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Rhizobium–plant signal exchange

Cited by 579 publications

References 93 publications

Disruption of sitA Compromises Sinorhizobium meliloti for Manganese Uptake Required for Protection against Oxidative Stress

Disruption of sitA Compromises Sinorhizobium meliloti for Manganese Uptake Required for Protection against Oxidative Stress

Sugar-Binding Activity of Pea Lectin Expressed in White Clover Hairy Roots

Nod factor‐induced host responses and mechanisms of Nod factor perception

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