1,721,024 research outputs found
Altered expression of Erwinia amylovora hrp genes in tobacco pretreated with bacterial protein-lipopolysaccharides
No full textInfiltration of protein-lipopolysaccharide complexes (pr LPS) (250 μg/ml) of Pseudomonas syringae pv. aptata into tobacco leaves protected against subsequent elicitation of the hypersensitive response (HR) by Erwinia amylovora. The effect of prLPS on the expression of E. amylovora hrp (hypersensitive response and pathogenicity) gencs was tested in protected tobacco leaves and in a defined medium in which hrp genes were highly expressed. Two,E. amylovora hrp loci transcriptionally fused with the Escherichia coli β-glucuronidase (Gus) coding sequence were used as chromosomal reporter genes. The prLPS treatment did not affect hrp gene expression of Hrp- mutants both in planta and in vitro, so the effect of prLPS treatment on hrp gene expression of two E. amylovora Hrp+ transformants was assayed during HR development in unprotected tissue and during the same time in prLPS protected tissue. A plasmid containing the same Gus fusions previously located in the chromosome was introduced into a wild-type strain of E. amylovora. Gus activity was significantly lower in protected tissue. We suggest that HR inhibition by prLPS treatment requires the entire hrp gene cluster in order for the bacteria to send a signal to the plant. which, in turn, inhibits the expression of hrp genes
Cloning of genes required for hypersensitivity and pathogenicity in Pseudomonas syringae pv. aptata
No full textA genomic library of Pseudomonas syringae pv. aptata strain NCPPB 2664, which causes bacterial blight of sugar beet, lettuce and other plants, was constructed in the cosmid vector pCPP31. The 13.4 kb EcoRI fragment of the cosmid pHIR11, containing the hrp (hypersensitive response and pathogenicity) gene cluster of the closely related bacterium Pseudomonas syringae pv. syringae strain 61, was used as a probe to identify a homologous hrp gene cluster in P. syringae pv. aptata. Thirty of 2500 cosmid clones, screened by colony hybridization, gave a strong hybridization signal with the probe, but none of these conferred to the non-pathogenic bacterium, Pseudomonas fluorescens, the ability to elicit the hypersensitive response (HR) in tobacco. Southern blot analysis of EcoRI-digested genomic DNA of P. syringae pv. aptata showed hybridizing bands of 12 kb and 4.4 kb. Only a 12 kb fragment hybridized in digests of the cosmids. Cosmid clone pCPP1069 was mutagenized with Tn 10-minitet and marker-exchanged into the genome of P. syringae pv. aptata. Three resulting prototrophic mutant strains failed to elicit the HR in tobacco and to cause disease in lettuce. The DNA flanking the Tn 10-minitet insertions from mutated derivatives of pCPP1069 hybridized with the 10.6 kb BglII fragment of pHIR11. These results indicate that P. syringae pv. aptata harbours hrp genes that are similar to, but arranged differently from, homologous hrp genes of P. syringae pv. syringae. © 1995 Kluwer Academic Publishers
Histochemistry of Tobacco Mesophyll Cell Walls Pretreated with Bacterial Protein‐lipopolysaccharides
No full textPrevention of hypersensitive confluent‐necrosis in tobacco mesophyll, caused by Pseudomonas syringae pv. aptata, and tolerance towards the incompatible bacterium are induced 48 h after intercellular injection of protein‐lipopolysaccharide complexes. Histochemical analysis and ultrastructural observations were carried out to determine whether there was an association between this tolerance state and cell wall alterations due to callose, lignin and/or suberin deposition either before or after challenge with the incompatible bacterium. No evidence was obtained for such wall alterations. Copyright © 1991, Wiley Blackwell. All rights reserve
No Evidence of Direct Superoxide Anion Effect in Hypersensitive Death of Pseudomonas syringae Van Hall in Tobacco Leaf Tissue
No full textThe hypothesis of superoxide anion generation as a direct bactericidal mechanism exercised by hypersensitive tobacco leaf tissue against an incompatible phytopathogenic pseudomonad was tested. The detection of O2− was made directly by reducing Cytochrome c and by producing nitrite from hydroxylamine chloride and indirectly by measuring the death of endophytic bacteria in the presence of superoxide dismutase. At 4 h and 6 h the low net specific reduction of Cytochrome c in the hypersensitive tissue was not confirmed by the specific production of nitrite. At the same time active superoxide dismutase did not give significant protection to the incompatible bacteria as compared to inactive superoxide dismutase. The protection provided by active superoxide dismutase as compared with the controls (bovine serum albumine treated tissue and non‐treated tissue) at 4 h and at 6 h was not correlated to its superoxide anion scavenger activity. The results indicated that the death of the incompatible pseudomonad during the hypersensitive reaction was not directly linked to O2− generation. Copyright © 1988, Wiley Blackwell. All rights reserve
Endophytic survival of Pseudomonas syringae pv. actinidiae in Actinidia chinensis 'Hort16A' plants
No full textTo tackle the epidemiological role of the latency phase of Pseudomonas syringae pv. actinidiae (Psa) in susceptible asymptomatic host plants, the pathogen survival and colonization were studied in seven-year-old plants of Actinidia chinensis ‘Hort16A’. The plants were inoculated with a virulent Psa gfp-expressing/rifampicin-resistant strain (Psagfp-Rifres) and the endophytic presence of Psa was determined by analysis of the whole plants to re-isolate Psagfp-Rifres and by PCR assays to confirm identity. Finally, the isolates were tested to verify their ability to induce disease symptoms and HR respectively in host and non-host plants. The Psagfp-Rifres presence inside the tissues of the experimentally contaminated plants was detected during the years following the inoculation. The data obtained showed that systemic colonization of host tissues by Psagfp-Rifres took place for a long period of time. The epidemiological significance of this finding raises questions about the effectiveness of the control measures to prevent bacterial canker solely based on antimicrobial treatment on plant surfaces
Identification and expression of the Pseudomonas syringae pv. aptata hrpZPsa gene which encodes an harpin elicitor
No full textA sequence homologous to an internal fragment 0.75 kb BstXI of the Pseudomonas syringae pv. syringae hrpZ gene was identified in Pseudomonas syringae pv. aptata NCPPB 2664, the causal agent of bacterial blight in sugar beet, lettuce and other plants, and in E. coli DH10B (pCCP1069) containing the P. syringae pv. aptata hrp gene cluster. PCR with oligonucleotides, based on the hrpZPss gene and used as primers with the total genomic DNA of P. syringae pv. aptata, amplified a 1 kb fragment that hybridized with the probe in highly stringent conditions. The amplicon was cloned into the pGEM® plasmid vector, amplified in E. coli DH5α and sequenced. The sequence showed 95%, 83% and 61% identity with those of hrpZPss, hrpZPsg and hrpZPst genes encoding the harpins of the P. syringae pv. syringae, glycinea and tomato, respectively. The amplicon was cloned into the pMAL® expression system. The expressed protein, fused with maltose-binding protein, was cleaved with a specific protease factor Xa, and purified using affinity chromatography. On the basis of the amino acid sequence and its ability to induce HR in tobacco leaves, it was identified as a P. syringae pv. aptata harpin
A reliable method for Pseudomonas syringae pv. actinidiae detection in kiwifruit explants during in vitro propagation
No full textAccording to recent statistics, in Italy a significant spread of the bacterial canker of Actinidia caused by Pseudomonas syringae pv. actinidiae (Psa) is recorded with peaks of 70 and 100%, and lower percentages ranging around 50%. The control of the Psa is a priority especially considering the hazard represented by the endophytic bacterial presence in nursery material. To evaluate the risk that could be associated with micropropagated shoots when using asymptomatic mother plants, Psa survival was studied in micro-propagated shoots of A. deliciosa ‘Hayward’ inoculated with different concentrations of a virulent Psa gfp-expressing/rifampicin-resistant strain (Psagfp-Rifres). Microbiological and molecular analysis were carried out at each in vitro transfer and on rooted plantlets in greenhouse. The Psagfp-Rifres reisolation on selective media confirmed by PCR analysis and by the ability to induce symptoms in Actinidia and HR in tobacco plants, was achieved in both the micropropagated materials and in the plants analyzed in toto after their re-establishment. A reliable and efficient method for Psa detection in nursery material is proposed to verify the presence Psa infection before symptom development
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Characterization of the mycoparasite Coniothyrium minitans: comparison between morpho-physiological and molecular analyses
No full textEight strains of the mycoparasite Coniothyrium minitans were analysed for intraspecific variation by three different approaches: analysis of morpho-physiological characteristics; random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analysis of the genomic DNA. A high variability in colony colour, gross morphology and conidial size was found depending on strain and culture conditions. All individual strains could be distinguished using the three type of analyses. However, a close correspondence between RAPD, AFLP patterns and morpho-physiological characteristics of C. minitans strains was not observed. Our results suggest AFLP analysis constituted a more efficient and reliable tool than RAPD analysis or morpho-physiological studies to detect intraspecific variability in C. minitans and to follow its fate after application in the field
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