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  • 1
    Electronic Resource
    Electronic Resource
    Rhizobial lipo-oligosaccharides: answers and questions (1992)
    Springer
    Plant molecular biology 20 (1992), S. 977-986 
    Details
    ISSN: 1573-5028
    Keywords: Chitin-derivatives ; lipo-oligosaccharides ; plant microbe interactions ; signal molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rhizobium bacteria produce certain lipo-oligosaccharides (modified chitin oligomers) after induction of nodulation (nod) gene transcription by the host plant. The function of the rhizobial nod genes in the biosynthesis of these lipo-oligosaccharides, focusing on their host specific aspects, is discussed. The lipo-oligosaccharides can elicit various responses in the host plants, like the formation of pre-infection threads and nodule meristems. Speculating on their function in plant morphogenesis the question is raised: do the rhizobial lipo-oligosaccharides resemble unknown plant signal molecules?
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027167
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Isolation, chemical structures and biological activity of the lipo-chitin oligosaccharide nodulation signals from Rhizobium etli (1995)
    Springer
    Plant molecular biology 29 (1995), S. 453-464 
    Details
    ISSN: 1573-5028
    Keywords: signal molecules ; host specificity ; nodulation ; flavonoids ; plant organogenesis ; mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rhizobium etli is a microsymbiont of plants of the genus Phaseolus. Using mass spectrometry we have identified the lipo-chitin oligosaccharides (LCOs) that are produced by R. etli strain CE3. They are N-acetylglucosamine pentasaccharides of which the non-reducing residue is N-methylated and N-acylated with cis-vaccenic acid (C18:1) or stearic acid (C18:0) and carries a carbamoyl group at C4. The reducing residue is substituted at the C6 position with O-acetylfucose. Analysis of their biological activity on the host plant Phaseolus vulgaris shows that these LCOs can elicit the formation of nodule primordia which develop to the stage where vascular bundles are formed. The formation of complete nodule structures, including an organized vascular tissue, is never observed. Considering the very close resemblance of the R. etli LCO structures to those of R. loti (I. M. López-Lara, J. D. J. van den Berg, J. E. Thomas Oates, J. Glushka, B. J. J. Lugtenberg, H. P. Spaink, Mol Microbiol 15: 627–638, 1995) we tested the ability of R. etli strains to nodulate various Lotus species and of R. loti to nodulate P. vulgaris. The results show that R. etli is indeed able to nodulate Lotus plants. However, several Lotus species are only nodulated when an additional flavonoid independent transcription activator (FITA) nodD gene is provided. Phaseolus plants can also be nodulated by R. loti bacteria, but only when the bacteria contain a FITA nodD gene. Apparently, the type of nod gene inducers secreted by the plants is the major basis for the separation of Phaseolus and Lotus into different cross inoculation groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020977
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The molecular basis of the host specificity of the Rhizobium bacteria (1994)
    Springer
    Antonie van Leeuwenhoek 65 (1994), S. 81-98 
    Details
    ISSN: 1572-9699
    Keywords: Nodulation genes ; plant-microbe interaction ; signal molecules ; symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The interaction between soil bacteria belonging to the generaRhizobium, Bradyrhizobium andAzorhizobium and leguminous plants results in the induction of a new plant organ, the root nodule. After invading these root nodulesvia infection threads the bacteria start to fix atmospheric nitrogen into ammonia which is beneficial for the host plant. This symbiotic interaction is highly host-specific in that each rhizobial strain is able to associate with only a limited number of host plant species. The subject of this presentation is the molecular mechanism by which the bacterium determines its host-specific characteristics. This mechanism appears to be based on at least two stages of molecular signaling between the bacterium and the plant host. In the first stage, flavonoids secreted by the plant root induce, in a host specific way, the transcription of bacterial genes which are involved in nodulation, the so-callednod genes. This leads to the second step of the signaling system: the production and secretion of lipo-oligosaccharide molecules by theRhizobium bacteria. These signal molecules, which are acylated forms of small fragments of chitin, have various discernable effects on the roots of the host plants. One of these effects is the dedifferentiation of groups of cells located in the cortex which leads to the formation of nodule meristems. In their mitogenic activity the bacterial signals resemble several well-known plant hormones like auxins and cytokinins. However, there are two major differences: (i) the bacterial signals lead to the induction of a specific organ and (ii) they are host-specific in that only the signals produced by compatible bacteria are able to induce meristems. Thenod genes determine this stage of host specificity by their essential role in the biosynthesis of the signal molecules. They appear to encode enzymes which are involved in the processes of fatty acid biosynthesis, fatty acid transfer, chitin synthesis and chitin modification. I will illustrate the statement that thenod gene products are ideal model enzymes for the study of these important processes because they are not needed in the free-living state of the bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00871750
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    Paper (German National Licenses)
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