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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Phytopathology 39 (2001), S. 27-52 
    ISSN: 0066-4286
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Biology
    Notes: Abstract Rhodococcus fascians infects a wide range of plants, initiating the formation of leafy galls that consist of centers of shoot amplification and shoot growth inhibition. R. fascians is an epiphyte but it also can establish endophytic populations. Bacterial signals involved in symptom development initiate de novo cell division and shoot meristem formation in differentiated tissues. The R. fascians signals exert activities that are distinct from mere cytokinin effects, and the evidence points to a process that adopted cytokinin biosynthetic enzymes to form derivatives with unique activity. Genes implicated in leafy gall formation are located on a linear plasmid and are subject to a highly controlling, complex regulatory network, integrating autoregulatory compounds and environmental signals. Leafy galls are considered as centers with specific metabolic features, a niche where populations of R. fascians experience a selective advantage. Such "metabolic habitat modification" might be universal for gall-inducing bacteria.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The ability of Rhodococcus fascians strain D188 to provoke leafy gall formation on a variety of plant species is correlated with the linear plasmid pFiD188, on which different pathogenicity loci were identified. The att locus affects the severity of symptom development on tobacco, whereas the fas locus is essential for virulence. To gain insight into the function of the att locus, sequence and expression analyses were performed. The att locus contains nine open reading frames homologous to arginine and β-lactam biosynthetic genes. att gene expression is transcriptionally induced by leafy gall extracts, but not by extracts of uninfected plants, and depends on the attR gene that encodes a LysR-type transcriptional regulator. The att locus proves to be essential for the formation of inducing factors (IFs) that are present in gall extracts. Because the induction of the fas locus also requires the presence of IFs in gall extracts, the att locus is proposed to play an important role in regulating the expression of the virulence loci of R. fascians.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The DNA region downstream of the nodABCSUIJ operon of Azorhizobium caulinodans was further characterized and two new genes, nodZ and noeC were identified in the same operon. The A. caulinodans wild-type strain produces a population of Nod factors that, at the reducing end, are either unmodified or carry a D-arabinosyl and/or an L-fucosyl branch. Nod factors produced by Tn5-insertion mutants in nodZnoeC, and the separate nolK locus, were analysed by thin-layer chromatography and mass spectrometry. Fucosylation of Nod factors depended on both nodZ and nolK. Arabinosylation depended on noeC and/or downstream genes. Protein extracts of A. caulinodans contained an enzymatic activity for fucose transfer from GDP-fucose to chitooligosaccharides and to Nod factors. By mutant analysis and expression of nodZ in Escherichia coli, the fucosyltransferase activity was ascribed to the protein encoded by nodZ. In addition, a Nod factor fucosyltransferase activity, independent of nodZ or other known nod genes, was detected in A. caulinodans. Finally, on the basis of sequence similarity of the nolK gene product, and mass spectrometric analysis of Nod factors produced by a nolK mutant, we propose that this gene is involved in the synthesis of GDP-fucose.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2048
    Keywords: Key words: Cell cycle –Digitalis– Leafy gall –Nicotiana– Micropropagation – Regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Rhodococcus fascians is a Gram-positive bacterium that infects dicotyledonous and monocotyledonous plants, leading to an alteration in the normal growth process of the host. The disease results from the modulation of the plant hormone balances, and cytokinins are thought to play an important role in the induction of symptoms. Generally, on the aerial parts of the plants, existing meristems were found to be most sensitive to the action of R. fascians, but, depending on the infection procedure, differentiated tissues as well gave rise to shoots. Similarly, in roots not only actively dividing cells, but also cells with a high competence to divide were strongly affected by R. fascians. The observed symptoms, together with the determined hormone levels in infected plant tissue, suggest that auxins and molecules of bacterial origin are also involved in leafy gall formation. The complexity of symptom development is furthermore illustrated by the necessary and continuous presence of the bacteria for symptom persistence. Indeed, elimination of the bacteria from a leafy gall results in the further development of the multiple embryonic buds of which it consists. This interesting characteristic offers novel biotechnological applications: a leafy gall can be used for germplasm storage and for plant propagation. The presented procedure proves to be routinely applicable to a very wide range of plants, encompassing several recalcitrant species.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2048
    Keywords: Key words: Defense response (plants) ; Leafy galls ; 7-Methyl esculin ; Nicotiana ; Rhodococcus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The chemical composition of ethanolic and aqueous extracts from leafy galls produced after infection of Nicotiana tabacum L. plants with Rhodococcus fascians was drastically changed compared to uninfected controls. Chlorogenic acid was abundant both in uninfected and infected plants, but caffeic acid and another cinnamoyl analogue were new in leafy galls. The most pronounced product induced in leafy galls was identified as 7-O-methyl-6-O-β-d-glucopyranosyl coumarin (7-methyl esculin). This is the first report of the presence of this coumarin derivative in tobacco. Interestingly, 7-methyl esculin did not accumulate in the presence of avirulent R. fascians strains nor was it found in leafy galls on other plant species. However, it did appear in crown galls induced by Agrobacterium tumefaciens on tobacco plants. Intriguingly, none of the phenolics known to accumulate in Solanaceae under pathogen attack were found in leafy galls. 7-Methyl esculin barely affected growth of R. fascians nor was it catabolized. Microscopical analysis showed that autofluorescent compounds were located mainly in the abundant meristematic regions of the leafy galls. We postulate that 7-methyl esculin might locally influence plant cell division.
    Type of Medium: Electronic Resource
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