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  • 1
    Electronic Resource
    Electronic Resource
    NoIR controls expression of the Rhizobium meliloti nodulation genes involved in the core Nod factor synthesis (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 15 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The synthesis of Rhizobium meliloti Nod signal molecules, encoded by the nod gene products, is finely regulated. A negative control of plasmid-borne nod gene expression is provided by the NoIR repressor encoded by the chromosomal noIR gene. NoIR was previously shown to downregulate the expression of the activator nodD1 gene and the common nodABC operon by binding to an overlapping region of the two promoters adjacent to the n1 nod-box (Kondorosi et al., 1989). We demonstrate here that NoIR also controls the expression of two additional genes, nodD2 and nodM, but does not directly regulate the expression of the host-specific nod genes located downstream of the n2, n3 and n5 nod-boxes. Thus, the nod genes are differentially regulated by NoIR and only those providing common nodulation functions, by determining the synthesis of the core Nod factor structure, are subjected to this negative regulation. Furthermore, NoIR has a strong negative effect on the production of Nod metabolites, the level of which may serve as a fine-tuning mechanism for optimal nodulation, specific to host-plant genotypes. In addition, it elicits preferential synthesis of Nod factors carrying unsaturated C16 fatty acids. Expression of noIR was high both in the free-living bacterium and in the bacteroid and it was downregulated by its own product and by the nod gene inducer luteolin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.tb02381.x
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  • 2
    Electronic Resource
    Electronic Resource
    Identification of two alfalfa early nodulin genes with homology to members of the pea Enod12 gene family (1993)
    Springer
    Plant molecular biology 21 (1993), S. 375-380 
    Details
    ISSN: 1573-5028
    Keywords: alfalfa ; early nodulin genes ; Enod12
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a search for plant genes expressed during early symbiotic interactions between Medicago sativa and Rhizobium meliloti, we have isolated and characterized two alfalfa genes which have strong sequence similarity to members of the Enod12 gene family of Pisum sativum. The M. sativa genes, MsEnod12A and B, encode putative protein products of 8066 Da and 12849 Da, respectively, each with a signal sequence at the N-terminus followed by a repetitive proline-rich region. Based on their expression during the initial period of nodule development, MsEnod12A and B are alfalfa early nodulin genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019952
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  • 3
    Electronic Resource
    Electronic Resource
    Isolation of a full-length mitotic cyclin cDNA clone CycIIIMs from Medicago sativa: Chromosomal mapping and expression (1995)
    Springer
    Plant molecular biology 27 (1995), S. 1059-1070 
    Details
    ISSN: 1573-5028
    Keywords: Alfalfa ; cell division cycle ; chromosomal location ; cyclin ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cyclins in association with the protein kinase p34cdc2and related cyclin-dependent protein kinases (cdks) are key regulatory elements in controlling the cell division cycle. Here, we describe the identification and characterization of a full-length cDNA clone of alfalfa mitotic cyclin, termed CycIIIMs. Computer analysis of known plant cyclin gene sequences revealed that this cyclin belongs to the same structural group as the other known partial alfalfa cyclin sequences. Genetic segregation analysis based on DNA-DNA hybridization data showed that the CycIIIMs gene(s) locates in a single chromosomal region on linkage group 5 of the alfalfa genetic map between RFLP markers UO89A and CG13. The assignment of this cyclin to the mitotic cyclin class was based on its cDNA-derived sequence and its differential expression during G2/M cell cycle phase transition of a partially synchronized alfalfa cell culture. Sequence analysis indicated common motifs with both the A- and B-types of mitotic cyclins similarly to the newly described B3-type of animal cyclins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020880
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  • 4
    Electronic Resource
    Electronic Resource
    Nod factors modulate the concentration of cytosolic free calcium differently in growing and non-growing root hairs of Medicago sativa L. (1999)
    Springer
    Planta 209 (1999), S. 207-212 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cytosolic free calcium ; Lipochitooligo saccharide ; Nodulation ; Rhizobium ; Signal transduction ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Using Ca2+-selective microelectrodes, the concentration of free calcium ([Ca2+]) in the cytosol has been measured in root hair cells of Medicago sativa L. in the presence of nodulation (Nod) factors. Growing root hairs of M. sativa displayed a steep apical [Ca2+] gradient, i.e. 604–967 nM in the tip compared with 95–235 nM in the basal region. When tested within the first 5 to 10 μm of the tip, addition of NodRm-IV(C16:2,S) decreased the cytosolic [Ca2+], whereas an increase was observed when tested behind the tip. Overall, this led to a partial dissipation of the [Ca2+] gradient. The Ca2+ response was specific: it was equally well observed in the presence of NodRm-IV(Ac,C16:2,S), reduced with NodRm-IV(C16:0,S), but not with chitotetraose, the nonactive glucosamine backbone. In contrast to growing root hairs, non-growing root hairs without a tip-to-base cytosolic [Ca2+] gradient responded to NodRm-IV(C16:2,S) with an increase in cytosolic [Ca2+] at the tip as well as at the root hair base. We suggest that the response to Nod factors depends on the stage of development of the root hairs, and that changes in cytosolic [Ca2+] may play different roles in Nod-factor signaling: changes of cytosolic [Ca2+] in the apical part of the root hair may be related to root hair deformation, while the increase in [Ca2+] behind the tip may be essential for the amplification of the Nod signal, for its propagation and transduction to trigger downstream events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050624
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  • 5
    Electronic Resource
    Electronic Resource
    Identification of host range determinants in the Rhizobium species MPIK3030 (1986)
    Springer
    Molecular genetics and genomics 203 (1986), S. 42-48 
    Details
    ISSN: 1617-4623
    Keywords: Host-range ; Tn5 mutagenesis ; hsn ; Nodulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary R. meliloti primarily nodulates Medicago sativa but cannot nodulate Macroptilium atropurpureum. By introducing an 11.4 kb region into R. meliloti from the Symplasmid of Rhizobium strain MPIK3030, the host range of the R. meliloti transconjugants were shown to be extended to M. atropurpureum, one of the hosts of MPIK3030 but not normally nodulated by R. meliloti. The region responsible for host range extension was isolated by mass conjugating a clone bank from MPIK3030 into the R. meliloti wild type, and subsequent screening for nodulation on M. atropurpureum. Using deleted derivatives of a plasmid reisolated from endosymbiotic bacteria, the host range region was further narrowed down to three EcoRI fragments. Tn5 mutagenesis allowed the isolation of three discrete regions on an 11.4 kb section, which are involved in the extension of host range to M. atropurpureum. Finally, complementation experiments performed with R. meliloti common nod and hsn mutants indicated that none of the genes involved in the early steps of nodulation, including host-range functions, can be complemented by genes carried on the 11.4 kb fragment derived from MPIK3030.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330382
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  • 6
    Electronic Resource
    Electronic Resource
    Physical and genetic analysis of a symbiotic region of Rhizobium meliloti: Identification of nodulation genes (1984)
    Springer
    Molecular genetics and genomics 193 (1984), S. 445-452 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A 135 kb long segment of the symbiotic region of the Rhizobium meliloti megaplasmid was mapped with the help of a Rhizobium meliloti gene library, made in the cosmid vehicle pJB8. A set of overlapping cosmid clones was used to identify the inserts in R-primes carrying megaplasmid sections, and to map 20 deletion mutations and 24 insertion mutations with Nod- or Fix- phenotypes. This led to the identification of DNA regions carrying nod or fix (nif) genes. The results of this study correlate well with transcription data of nodule-specific expression of plasmid sequences. The nod mutations were localized in two groups. Using directed Tn5 mutagenesis, correlated physical-genetic maps for these regions were established. One nod gene cluster is about 2.5–3.0 kb in size and carries genes involved in root hair curling, a very early step in nodule formation. Mutations in these genes can be complemented by sym plasmids of other Rhizobium species, such as Rhizobium leguminosarum. We designate these genes as “common” nod genes because mutations in them can be complemented by plasmids derived from different Rhizobium strains. The other nod gene cluster consists of a 2 kb and a 1 kb long DNA segment, separated by a 1 kb region nonessential for nodulation. These nod genes are probably involved in the host specificity of nodulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382082
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  • 7
    Electronic Resource
    Electronic Resource
    Identification and cloning of nodulation genes from the wide host range Rhizobium strain MPIK3030 (1985)
    Springer
    Molecular genetics and genomics 199 (1985), S. 271-278 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A 70 kbp segment of the megaplasmid from a broad host range Rhizobium strain (MPIK3030) was mapped with the aid of cosmid clones made in the vector pJB8. A 7.9 kbp EcoRI fragment from this region, 55 kbp away from the nif gene cluster, was shown to hybridize to the “common” nod genes from R. meliloti. Using several R. meliloti nod probes it was possible to delimit an 830 bp region as being the center of greatest homology. Sequence data from two sections of this region gave a nucleotide homology of 73.7% to the nodC gene of R. meliloti. Using Tn5 mutagenesis a clone was isolated carrying Tn5 in the highly homologous region. When tested on Macroptilium atropurpureum, this MPIK3030 derivative was shown to have a Nod− phenotype. When the wild-type allele was reintroduced into the Tn5 mutant, nodulation was restored. Interspecies complementation also showed that both R. meliloti and Rhizobium sp. MPIK3030 nod regions were able to restore nodulation to Tn5-induced nodC mutants from either strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330269
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  • 8
    Electronic Resource
    Electronic Resource
    Construction and characterization of R-prime plasmids carrying symbiotic genes of R. meliloti (1983)
    Springer
    Molecular genetics and genomics 189 (1983), S. 129-135 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary R-prime plasmids carrying 100–200 kb regions of R. meliloti DNA coding for symbiotic functions were isolated from a Km8 derivative of R68.45. The R-primes were obtained from matings between R. meliloti strains containing Tn5-induced symbiotic mutations and E. coli recipients by selecting for the kanamycin resistance marker of Tn5. It was demonstrated that the regions inserted into the R-primes were identical with those DNA segments where Tn5 was located in the respective parental R. meliloti. R-primes were generated from both the R. meliloti chromosome and from the megaplasmid pRme41b. A set of R-primes, carrying the nitrogen fixation (nif) gene cluster, also carried genes required for nodulation (nod genes) of alfalfa. Transfer of these R-primes into different Nod- mutants restored the Nod+ phenotype. When they were introduced into A. tumefaciens the transconjugants formed small nodules on alfalfa. This indicates that nodulation and nitrogen fixation genes of the R. meliloti megaplasmid are clustered on a relatively short DNA segment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326065
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  • 9
    Electronic Resource
    Electronic Resource
    Positive involvemetn of ppGpp in derepression of the nif operon in Klebsiella pneumoniae (1982)
    Springer
    Molecular genetics and genomics 185 (1982), S. 198-204 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The kinetics of derepression of the enzyme nitrogenase were investigated, after exhaustion of a limiting amount of ammonium from the culture medium, in a prototrophic stringent-relaxed pair of Klebsiella pneumoniae strains and in their F′ relA +-F′ relA derivatives. The results indicate that ppGpp (guanosine 3′–5′ diphosphate) increases the nitrogen fixation capability of K. pneumoniae by at least three different mechanisms. (1) It prevents exhaustion of the ATP pool when nitrogen starvation is imposed. (2) The translational defects in relaxed mutants are suppressed by ppGpp during nif derepression. (3) The synthesis of nitrogenase components is at least five times higher in the presence of ppGpp than in its absence. This latter conclusion was based on experimental results obtained when following the incorporation of (35S)-methionine into nitrogenase components after pulse labelling at various time intervals during nif derepression. The nitrogenase components were separated by solid phase radioimmunoassay as well as by two-dimensional gel electrophoresis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330786
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  • 10
    Electronic Resource
    Electronic Resource
    Cell cycle regulation in the course of nodule organogenesis in Medicago (2000)
    Springer
    Plant molecular biology 43 (2000), S. 773-786 
    Details
    ISSN: 1573-5028
    Keywords: cell cycle ; de novo meristem ; differentiation ; endoreduplication ; Nod factor ; nodule organogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The molecular mechanisms of de novo meristem formation, cell differentiation and the integration of the cell cycle machinery into appropriate stages of the developmental programmes are still largely unknown in plants. Legume root nodules, which house nitrogen-fixing rhizobia, are unique plant organs and their development may serve as a model for organogenetic processes in plants. Nodules form and are essential for the plant only under limitation of combined nitrogen in the soil. Moreover, their development is triggered by external mitogenic signals produced by their symbiotic partners, the rhizobia. These signals, the lipochitooligosaccharide Nod factors, act as host-specific morphogens and induce the re-entry of root cortical cells into mitotic cycles. Maintenance of cell division activity leads to the formation of a persistent nodule meristem from which cells exit continuously and enter the nodule differentiation programme, involving multiple cycles of endoreduplication and enlargement of nuclear and cell volumes. While the small diploid 2C cells remain uninfected, the large polyploid cells can be invaded and, after completing the differentiation programme, host the nitrogen-fixing bacteroids. This review summarizes the present knowledge on cell cycle reactivation and meristem formation in response to Nod factors and reports on a novel plant cell cycle regulator that can switch mitotic cycles to differentiation programmes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006405029600
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