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PubMed2002

A gene in the Pseudomonas syringae pv. tomato Hrp pathogenicity island conserved effector locus, hopPtoA1, contributes to efficient formation of bacterial colonies in planta and is duplicated elsewhere in the genome.

The ability of Pseudomonas syringae to grow in planta is thought to be dependent upon the Hrp (type III secretion) system and multiple effector proteins that this system injects into plant cells. ORF5 in the conserved effector locus of the P. syringae pv. tomato DC3000 Hrp pathogenicity island was shown to encode a Hrp-secreted protein and to have a similarly secreted homolog encoded in an effector-rich pathogenicity island located elsewhere in the genome. These putative effector genes were designated hopPtoA1 and hopPtoA2, respectively. DNA gel blot analysis revealed that sequences hybridizing with hopPtoA1 were widespread among P. syringae pathovars, and some strains, like DC3000, appear to have two copies of the gene. uidA transcriptional fusions revealed that expression of hopPtoA1 and hopPtoA2 can be activated by the HrpL alternative sigma factor. hopPtoA1 and hopPtoA1/hopPtoA2 double mutants were not obviously different from wild-type P. syringae pv. tomato DC3000 in their ability to produce symptoms or to increase their total population size in host tomato and Arabidopsis leaves. However, confocal laser-scanning microscopy of GFP (green fluorescent protein)-labeled bacteria in Arabidopsis leaves 2 days after inoculation revealed that the frequency of undeveloped individual colonies was higher in the hopPtoA1 mutant and even higher in the hopPtoA1/hopPtoA2 double mutant. These results suggest that hopPtoA1 and hopPtoA2 contribute redundantly to the formation of P. syringae pv. tomato DC3000 colonies in Arabidopsis leaves.

Amino Acid Sequence↗
PubMed1994

Two native plasmids of Pseudomonas syringae pathovar tomato strain PT23 share a large amount of repeated DNA, including replication sequences.

Strain PT23 of Pseudomonas syringae pv. tomato contains four native plasmids, designated A, B, C, and D. By DNA hybridization of genomic and plasmid DNA digests from the wild type and a plasmid-cured strain, we determined that c. 61 kb (c. 74%) of pPT23B is repeated in pPT23 A and only c. 17 kb (c. 21%) is in single copy in strain PT23. pPT23B also contains DNA repeated in the chromosome that occurs in three DNA fragments of 0.6, 4.6, and 9.6 kb that might be transposable elements. Additionally, the 9.6 kb fragment also shares sequences with the three other plasmids of strain PT23. By DNA hybridization with the origin of replication from a native plasmid of P. syringae pv. syringae and in vivo replication tests, we identified the origins of replication of plasmids A, B, and D and showed that they cross-hybridize. The putative par region from pPT23 A has also been identified and is not conserved in the other three native plasmids from strain PT23. By using the defined minimal origin of replication from pPT23 A as a probe, we showed that it is highly conserved in 14 strains belonging to nine different pathovars of P. syringae and that as many as five different native plasmids with closely related origins of replication coexist in the same cell. The duplication and reorganization of plasmids might therefore occur at high frequency and could be responsible for the existence of large numbers of native plasmids in P. syringae strains.

Base Sequence↗
PubMed1989

Influence of Pseudomonas syringae culture conditions on initiation of the hypersensitive response of culture tobacco cells.

The inhibitor sensitivity and timing of the ionic response of suspension-cultured tobacco cells were used as a bioassay for the Pseudomonas syringae signal that elicits the hypersensitive response in resistant plants. The ionic response of tobacco cell suspensions inoculated with P. syringae pv. syringae 61 and P. syringae pv. pisi grown in rich media was inhibited by rifampin, tetracycline, and streptomycin during a 2- to 2.5-h induction stage. Coculturing the bacteria with tobacco cells for 3 h or more before inoculating fresh tobacco cells specifically abolished the sensitivity of the ionic response to these inhibitors and reduced the response time of the tobacco cells from 3 to 1 h. The apparent activation of the bacteria during coculture was not dependent on the plant cells and could be achieved by incubating the bacteria in a nitrogen-deficient medium containing a metabolizable carbon source. Addition of proteose peptone and Casamino Acids to this medium suppressed activation of the bacteria. The results suggest that the hypersensitive response-eliciting signal forms late in the induction stage, perhaps as a result of the derepression of some of the P. syringae genes functional in elicitation of the hypersensitive response. The nature of the activated state remains elusive but is consistent with the accumulation of protein(s) whose activity indirectly elicits the ionic response.

Biological Assay↗
PubMed1993

Invasion and Exclusion among Coexisting Pseudomonas syringae Strains on Leaves.

The invasion and exclusion abilities of coexisting Pseudomonas syringae strains were quantified on leaves. Twenty-nine P. syringae strains were inoculated onto plants in 107 pairwise combinations. All pairs were duplicated so that each strain was inoculated both first as an antagonist strain (day 0) and second as a challenge strain (day 3). The population size of each strain in a mixture was quantified on day 6 following incubation under moist conditions. For P. syringae strains, the presence of an established population often significantly reduced the growth of subsequently arriving challenge strains on the leaf surface. Invasion and exclusion abilities, quantified by contrasting population sizes of challenge strains in the presence and in the absence of another strain, varied significantly among P. syringae strains and were partly a function of the particular strain pair. The population size of a strain when present alone on a leaf was not predictive of invasion or exclusion ability. Successful invaders were significantly less likely to exclude challenge populations than were nonsuccessful invaders. Population sizes of successful excluders were negatively correlated with population sizes of coexisting challenge strains, while population sizes of successful invaders were positively correlated with those of coexisting antagonist strains. The patterns of interaction among coexisting strains suggest mechanisms for successful invasion and exclusion among P. syringae strains on leaves.

Journal Article↗
PubMed1994

Genetic and plasmid diversity within natural populations of Pseudomonas syringae with various exposures to copper and streptomycin bactericides.

We examined the genetic and plasmid diversity within natural populations of Pseudomonas syringae isolated from three ornamental pear nurseries in eastern Oklahoma. The bactericide spray regimen differed at each nursery; copper and streptomycin, only copper, and no bactericides were applied at nurseries I, II, and III respectively. Resistance to copper (Cur) and resistance to streptomycin (Smr) were determined for 1,938 isolates of P. syringae; isolates from nurseries I and II were generally Cur Sms; whereas most isolates from nursery III were Cus Sms. The plasmid profiles of 362 isolates were determined, and six, one, seven, and four plasmid profiles were obtained for Cur, Smr, Cur Smr, and Cus Sms isolates, respectively. All Smr plasmids contained sequences homologous to the strA and strB Smr genes from broad-host-range plasmid RSF1010 and were associated with Smr transposon Tn5393. Plasmids were placed into two groups on the basis of hybridization to the oriV and par sequences from pOSU900, a cryptic plasmid in P. syringae pv. syringae. A total of 100 randomly chosen P. syringae isolates from nurseries I and III were analyzed for genetic diversity by using the arbitrarily primed PCR (AP-PCR) technique. An analysis of chromosomal genotypes by AP-PCR revealed a high degree of genetic diversity among the isolates, and the results of this analysis indicated that the isolates could be clustered into two distinct groups. The plasmid profiles were specific to isolates belonging to particular AP-PCR groups. Within each AP-PCR group, identical plasmid profiles were produced by isolates that had different chromosomal genotypes, implying that plasmid transfer has played an important role in the dissemination of Cur and Smr within the populations studied.

Base Sequence↗
PubMed2001

Construction and analysis of photolyase mutants of Pseudomonas aeruginosa and Pseudomonas syringae: contribution of photoreactivation, nucleotide excision repair, and mutagenic DNA repair to cell survival and mutability following exposure to UV-B radiation.

Based on nucleotide sequence homology with the Escherichia coli photolyase gene (phr), the phr sequence of Pseudomonas aeruginosa PAO1 was identified from the genome sequence, amplified by PCR, cloned, and shown to complement a known phr mutation following expression in Escherichia coli SY2. Stable, insertional phr mutants containing a tetracycline resistance gene cassette were constructed in P. aeruginosa PAO1 and P. syringae pv. syringae FF5 by homologous recombination and sucrose-mediated counterselection. These mutants showed a decrease in survival compared to the wild type of as much as 19-fold after irradiation at UV-B doses of 1,000 to 1,550 J m(-2) followed by a recovery period under photoreactivating conditions. A phr uvrA mutant of P. aeruginosa PAO1 was markedly sensitive to UV-B irradiation exhibiting a decrease in survival of 6 orders of magnitude following a UV-B dose of 250 J m(-2). Complementation of the phr mutations in P. aeruginosa PAO1 and P. syringae pv. syringae FF5 using the cloned phr gene from strain PAO1 resulted in a restoration of survival following UV-B irradiation and recovery under photoreactivating conditions. The UV-B survival of the phr mutants could also be complemented by the P. syringae mutagenic DNA repair determinant rulAB. Assays for increases in the frequency of spontaneous rifampin-resistant mutants in UV-B-irradiated strains containing rulAB indicated that significant UV-B mutability (up to a 51-fold increase compared to a nonirradiated control strain) occurred even in the wild-type PAO1 background in which rulAB only enhanced the UV-B survival by 2-fold under photoreactivating conditions. The frequency of occurrence of spontaneous nalidixic acid-resistant mutants in the PAO1 uvrA and uvrA phr backgrounds complemented with rulAB were 3.8 x 10(-5) and 2.1 x 10(-3), respectively, following a UV-B dose of 1,550 J m(-2). The construction and characterization of phr mutants in the present study will facilitate the determination of the roles of light and dark repair systems in organisms exposed to solar radiation in their natural habitats.

Cloning, Molecular↗
PubMed2001

Characterization of fluorescent and nonfluorescent peptide siderophores produced by Pseudomonas syringae strains and their potential use in strain identification.

Nonfluorescent highly virulent strains of Pseudomonas syringae pv. aptata isolated in different European countries and in Uruguay produce a nonfluorescent peptide siderophore, the production of which is iron repressed and specific to these strains. The amino acid composition of this siderophore is identical to that of the dominant fluorescent peptide siderophore produced by fluorescent P. syringae strains, and the molecular masses of the respective Fe(III) chelates are 1,177 and 1,175 atomic mass units. The unchelated nonfluorescent siderophore is converted into the fluorescent siderophore at pH 10, and colors and spectral characteristics of the unchelated siderophores and of the Fe(III)-chelates in acidic conditions are similar to those of dihydropyoverdins and pyoverdins, respectively. The nonfluorescent siderophore is used by fluorescent and nonfluorescent P. syringae strains. These results and additional mass spectrometry data strongly suggest the presence of a pyoverdin chromophore in the fluorescent siderophore and a dihydropyoverdin chromophore in the nonfluorescent siderophore, which are both ligated to a succinamide residue. When chelated, the siderophores behave differently from typical pyoverdins and dihydropyoverdins in neutral and alkaline conditions, apparently because of the ionization occurring around pH 4.5 of carboxylic acids present in beta-hydroxyaspartic acid residues of the peptide chains. These differences can be detected visually by pH-dependent changes of the chelate colors and spectrophotochemically. These characteristics and the electrophoretic behavior of the unchelated and chelated siderophores offer new tools to discriminate between saprophytic fluorescent Pseudomonas species and fluorescent P. syringae and P. viridiflava strains and to distinguish between the two siderovars in P. syringae pv. aptata.

Culture Media↗
PubMed2002

Reduction of olive knot disease by a bacteriocin from Pseudomonas syringae pv. ciccaronei.

A bacteriocin produced by Pseudomonas syringae pv. ciccaronei, used at different purification levels and concentrations in culture and in planta, inhibited the multiplication of P. syringae subsp. savastanoi, the causal agent of olive knot disease, and affected the epiphytic survival of the pathogen on the leaves and twigs of treated olive plants. Treatments with bacteriocin from P. syringae pv. ciccaronei inhibited the formation of overgrowths on olive plants caused by P. syringae subsp. savastanoi strains PVBa229 and PVBa304 inoculated on V-shaped slits and on leaf scars at concentrations of 10(5) and 10(8) CFU ml(-1), respectively. In particular, the application of 6,000 arbitrary units (AU) of crude bacteriocin (dialyzed ammonium sulfate precipitate of culture supernatant) ml(-1) at the inoculated V-shaped slits and leaf scars resulted in the formation of knots with weight values reduced by 81 and 51%, respectively, compared to the control, depending on the strains and inoculation method used. Crude bacteriocin (6,000 AU ml(-1)) was also effective in controlling the multiplication of epiphytic populations of the pathogen. In particular, the bacterial populations recovered after 30 days were at least 350 and 20 times lower than the control populations on twigs and on leaves, respectively. These results suggest that bacteriocin from P. syringae pv. ciccaronei can be used effectively to control the survival of the causal agent of olive knot disease and to prevent its multiplication at inoculation sites.

Bacteriocins↗
PubMed1993

Characterization of the promoter of avirulence gene D from Pseudomonas syringae pv. tomato.

The avirulence gene D (avrD) from Pseudomonas syringae pv. tomato comprises the first open reading frame (ORF) of a putative operon consisting of at least five tandem ORFs. The promoter of the avrD operon was localized to a 150-bp DNA fragment occurring 5' to the avrD gene by using the Tn7-lux and gus reporter systems. The avrD promoter in P. syringae pv. tomato and P. syringae pv. glycinea was poorly expressed when bacteria were grown in complex culture media but was activated during bacterial growth in plants. The timing and level of induction were similar in compatible and incompatible plant-pathogen interactions. When bacteria were grown in minimal culture medium, promoter activity was repressed by certain carbon sources, high concentrations of nitrogen compounds, and pH values above 6.5. Primer extension experiments on RNA from bacteria grown in minimal medium identified two transcription initiation sites 87 and 41 nucleotides upstream from the translational start site. Only the -41 transcriptional start site was identified in bacteria grown in soybean leaves. A sigma 54 promoter consensus sequence (GG-10 bp-GC) occurred 14 bp upstream of the -41 transcriptional start, and 3' deletions into this region completely abolished promoter activity. Little expression was observed when a gus fusion with the avrD promoter was introduced into an ntrA mutant strain of P. syringae pv. phaseolicola deficient in the sigma 54 cofactor. Expression from the avrD promoter also required the hrp regulatory genes, hrpS and hrpL. Deletions from the 5' end of the promoter region and base substitution analyses also identified two upstream elements important for expression. Sequence comparison of these elements with other cloned avirulence genes revealed the presence of a conserved consensus sequence elements with other cloned avirulence genes revealed the presence of a conserved consensus sequence (GGAACC-N15/16-CCAC) in the promoters of nine different avirulence genes from P. syringae pathovers.

Amino Acid Sequence↗
PubMed1999

The Avr (effector) proteins HrmA (HopPsyA) and AvrPto are secreted in culture from Pseudomonas syringae pathovars via the Hrp (type III) protein secretion system in a temperature- and pH-sensitive manner.

We present here data showing that the Avr proteins HrmA and AvrPto are secreted in culture via the native Hrp pathways from Pseudomonas syringae pathovars that produce these proteins. Moreover, their secretion is strongly affected by the temperature and pH of the culture medium. Both HrmA and AvrPto were secreted at their highest amounts when the temperature was between 18 and 22 degrees C and when the culture medium was pH 6.0. In contrast, temperature did not affect the secretion of HrpZ. pH did affect HrpZ secretion, but not as strongly as it affected the secretion of HrmA. This finding suggests that there are at least two classes of proteins that travel the P. syringae pathway: putative secretion system accessory proteins, such as HrpZ, which are readily secreted in culture; and effector proteins, such as HrmA and AvrPto, which apparently are delivered inside plant cells and are detected in lower amounts in culture supernatants under the appropriate conditions. Because HrmA was shown to be a Hrp-secreted protein, we have changed the name of hrmA to hopPsyA to reflect that it encodes a Hrp outer protein from P. syringae pv. syringae. The functional P. syringae Hrp cluster encoded by cosmid pHIR11 conferred upon P. fluorescens but not Escherichia coli the ability to secrete HopPsyA in culture. The use of these optimized conditions should facilitate the identification of additional proteins traveling the Hrp pathway and the signals that regulate this protein traffic.

Bacterial Outer Membrane Proteins↗
PubMed1999

Immunochemical characterization and taxonomic evaluation of the O polysaccharides of the lipopolysaccharides of Pseudomonas syringae serogroup O1 strains.

The O polysaccharide (OPS) of the lipopolysaccharide (LPS) of Pseudomonas syringae pv. atrofaciens IMV 7836 and some other strains that are classified in serogroup O1 was shown to be a novel linear alpha-D-rhamnan with the tetrasaccharide O repeat -->3)-alpha-D-Rhap-(1-->3)-alpha-D-Rhap-(1-->2)-alpha-D-R hap-(1-->2)- alpha-D-Rhap-(1--> (chemotype 1A). The same alpha-D-rhamnan serves as the backbone in branched OPSs with lateral (alpha1-->3)-linked D-Rhap, (beta1-->4)-linked D-GlcpNAc, and (alpha1-->4)-linked D-Fucf residues (chemotypes 1B, 1C, and 1D, respectively). Strains of chemotype 1C demonstrated variations resulting in a decrease of the degree of substitution of the backbone 1A with the lateral D-GlcNAc residue (chemotype 1C-1A), which may be described as branched regular left arrow over right arrow branched irregular --> linear OPS structure alterations (1Cleft arrow over right arrow 1C-1A --> 1A). Based on serological data, chemotype 1D was suggested to undergo a 1D left arrow over right arrow 1D-1A alteration, whereas chemotype 1B showed no alteration. A number of OPS backbone-specific monoclonal antibodies (MAbs), Ps(1-2)a, Ps(1-2)a(1), Ps1a, Ps1a(1), and Ps1a(2), as well as MAbs Ps1b, Ps1c, Ps1c(1), Ps1d, Ps(1-2)d, and Ps(1-2)d(1) specific to epitopes related to the lateral sugar substituents of the OPSs, were produced against P. syringae serogroup O1 strains. By using MAbs, some specific epitopes were inferred, serogroup O1 strains were serotyped in more detail, and thus, the serological classification scheme of P. syringae was improved. Screening with MAbs of about 800 strains representing all 56 known P. syringae pathovars showed that the strains classified in serogroup O1 were found among 15 pathovars and the strains with the linear OPSs of chemotype 1A were found among 9 of the 15 pathovars. A possible role for the LPS of P. syringae and related pseudomonads as a phylogenetic marker is discussed.

Antibodies, Monoclonal↗
PubMed1999

Thermoregulated expression and characterization of an NAD(P)H-dependent 2-cyclohexen-1-one reductase in the plant pathogenic bacterium Pseudomonas syringae pv. glycinea.

The phytopathogenic bacterium Pseudomonas syringae pv. glycinea PG4180.N9 causes bacterial blight of soybeans and preferably infects its host plant during periods of cold, humid weather conditions. To identify proteins differentially expressed at low temperatures, total cellular protein fractions derived from PG4180.N9 grown at 18 and 28 degreesC were separated by two-dimensional gel electrophoresis. Of several proteins which appeared to be preferentially present at 18 degreesC, a 40-kDa protein with an isoelectric point of approximately 5 revealed significant N-terminal sequence homology to morphinone reductase (MR) of Pseudomonas putida M10. The respective P. syringae gene was isolated from a genomic cosmid library of PG4180, and its nucleotide sequence was determined. It was designated ncr for NAD(P)H-dependent 2-cyclohexen-1-one reductase. Comparison of the 1,083-bp open reading frame with database entries revealed 48% identity and 52% similarity to the MR-encoding morB gene of P. putida M10. The ncr gene was overexpressed in Escherichia coli, and its gene product was used to generate polyclonal antisera. Purified recombinant Ncr protein was enzymatically characterized with NAD(P)H and various morphinone analogs as substrates. So far, only 2-cyclohexen-1-one and 3-penten-2-one were found to be substrates for Ncr. By high-pressure liquid chromatography analysis, flavin mononucleotide could be identified as the noncovalently bound prosthetic group of this enzyme. The distribution of the ncr gene in different Pseudomonas species and various strains of P. syringae was analyzed by PCR and Southern blot hybridization. The results indicated that the ncr gene is widespread among P. syringae pv. glycinea strains but not in other pathovars of P. syringae or in any of the other Pseudomonas strains tested.

Amino Acid Sequence↗
PubMed2000

Regulation of the rulAB mutagenic DNA repair operon of Pseudomonas syringae by UV-B (290 to 320 nanometers) radiation and analysis of rulAB-mediated mutability in vitro and in planta.

The effects of the rulAB operon of Pseudomonas syringae on mutagenic DNA repair and the transcriptional regulation of rulAB following irradiation with UV-B wavelengths were determined. For a rulB::Km insertional mutant constructed in P. syringae pv. syringae B86-17, sensitivity to UV-B irradiation increased and UV mutability decreased by 12- to 14-fold. rulAB-induced UV mutability was also tracked in phyllosphere populations of B86-17 for up to 5 days following plant inoculation. UV mutability to rifampin resistance (Rif(r)) was detected at all sampling points at levels which were significantly greater than in nonirradiated controls. In P. aeruginosa PAO1, the cloned rulAB determinant on pJJK17 conferred a 30-fold increase in survival and a 200-fold increase in mutability following a UV-B dose of 1,900 J m(-2). In comparative studies using defined genetic constructs, we determined that rulAB restored mutability to the Escherichia coli umuDC deletion mutant RW120 at a level between those of its homologs mucAB and umuDC. Analyses using a rulAB::inaZ transcriptional fusion in Pseudomonas fluorescens Pf5 showed that rulAB was rapidly induced after UV-B irradiation, with expression levels peaking at 4 h. At the highest UV-B dose administered, transcriptional activity of the rulAB promoter was elevated as much as 261-fold compared to that of a nonirradiated control. The importance of rulAB for survival of P. syringae in its phyllosphere habitat, coupled with its wide distribution among a broad range of P. syringae genotypes, suggests that this determinant would be appropriate for continued investigations into the ecological ramifications of mutagenic DNA repair.

DNA Repair↗
PubMed2026

Chloroplast genome comparative analysis and phylogenetic relationships of 15 Syringa species (Oleaceae).

Syringa is a crucial shrub genus in the family Oleaceae, which has significant ornamental, economic, and medicinal value. However, research on the chloroplast genome (CPG) phylogeny and lineage diversification of this genus remains limited. In this study, all 15 Syringa CPGs exhibited a characteristic quadripartite structure, with genome lengths ranging from 154,019-158,020 bp. These CPGs were highly conserved and moderately differentiated, each containing 130-132 genes. Analysis of inverted repeat (IR) boundaries indicated structural conservation, with six genes: rps19, rpl2, ycf1, trnN, ndhF, and trnH present at the IR/single-copy (SC) junctions. The small single copy (SSC) region displayed greater sequence variability than the IR regions. ycf1, ndhH, trnL-rpl32, ndhF-ycf1, and rbcL-accD were identified as potential molecular markers and rps11, ycf2, and ycf4 may have contributed to the adaptive evolution of Syringa. Phylogenetic reconstruction based on whole CPG data supported the monophyly of the 15 species, which were divided into three distinct subclades. Molecular dating estimated that Syringa diverged from its sister genus approximately 58 million years ago, with most Syringa species diversifying further approximately 47.49 million years ago during the Eocene. Our findings will hopefully stimulate further studies on this genus that may enhance biodiversity knowledge.

Journal Article↗
PubMed2003

Differential volatile emissions and salicylic acid levels from tobacco plants in response to different strains of Pseudomonas syringae.

Pathogen-induced plant responses include changes in both volatile and non-volatile secondary metabolites. To characterize the role of bacterial pathogenesis in plant volatile emissions, tobacco plants, Nicotiana tabacum L. K326, were inoculated with virulent, avirulent, and mutant strains of Pseudomonas syringae. Volatile compounds released by pathogen-inoculated tobacco plants were collected, identified, and quantified. Tobacco plants infected with the avirulent strains P. syringae pv. maculicola ES4326 (Psm ES4326) or pv. tomato DC3000 (Pst DC3000), emitted quantitatively different, but qualitatively similar volatile blends of (E)-beta-ocimene, linalool, methyl salicylate (MeSA), indole, caryophyllene, beta-elemene, alpha-farnesene, and two unidentified sesquiterpenes. Plants treated with the hrcC mutant of Pst DC3000 (hrcC, deficient in the type-III secretion system) released low levels of many of the same volatile compounds as in Psm ES4326- or Pst DC3000-infected plants, with the exception of MeSA, which occurred only in trace amounts. Interaction of the virulent pathogen P. syringae pv. tabaci (Pstb), with tobacco plants resulted in a different volatile blend, consisting of MeSA and two unidentified sesquiterpenes. Overall, maximum volatile emissions occurred within 36 h post-inoculation in all the treatments except for the Pstb infection that produced peak volatile emissions about 60 h post-inoculation. (E)-beta-Ocimene was released in a diurnal pattern with the greatest emissions during the day and reduced emissions at night. Both avirulent strains, Psm ES4326 and Pst DC3000, induced accumulation of free salicylic acid (SA) within 6 h after inoculation and conjugated SA within 60 h and 36 h respectively. In contrast, SA inductions by the virulent strain Pstb occurred much later and conjugated SA increased slowly for a longer period of time, while the hrcC mutant strain did not trigger free and conjugated SA accumulations in amounts significantly different from control plants. Jasmonic acid, known to induce plant volatile emissions, was not produced in significantly higher levels in inoculated plants compared to the control plants in any treatments, indicating that induced volatile emissions from tobacco plants in response to P. syringae are not linked to changes in jasmonic acid.

Cyclopentanes↗
PubMed2004

Psychrophilic Pseudomonas syringae requires trans-monounsaturated fatty acid for growth at higher temperature.

A psychrophilic bacterium, Pseudomonas syringae (Lz4W) from Antarctica, was used as a model system to establish a correlation, if any, between thermal adaptation, trans-fatty acid content and membrane fluidity. In addition, attempts were made to clone and sequence the cti gene of P. syringae (Lz4W) so as to establish its characteristics with respect to the cti of other Pseudomonas spp. and also to in vitro mutagenize the cti gene so as to generate a cti null mutant. The bacterium showed increased proportion of saturated and trans-monounsaturated fatty acids when grown at 28 degrees C compared to cells grown at 5 degrees C, and the membrane fluidity decreased with growth temperature. In the mutant, the trans-fatty acid was not synthesized, and the membrane fluidity also decreased with growth temperature, but the decrease was not to the extent that was observed in the wild-type cells. Thus, it would appear that synthesis of trans-fatty acid and modulation of membrane fluidity to levels comparable to the wild-type cells is essential for growth at higher temperatures since the mutant exhibits growth arrest at 28 degrees C. In fact, the cti null mutant-complemented strain of P. syringae (Lz4W-C30b) that was capable of synthesizing the trans-fatty acid was indeed capable of growth at 28 degrees C, thus confirming the above contention. The cti gene of P. syringae (Lz4W) that was cloned and sequenced exhibited high sequence identity with the cti of other Pseudomonas spp. and exhibited all the conserved features.

Bacteria↗
PubMed2005

Extracytoplasmic function sigma factors in Pseudomonas syringae.

Genome analyses of the plant pathogens Pseudomonas syringae pv. tomato DC3000, pv. syringae B728a and pv. phaseolicola 1448A reveal fewer extracytoplasmic function (ECF) sigma factors than in related Pseudomonads with different lifestyles. We highlight the presence of a P. syringae-specific ECF sigma factor that is an interesting target for future studies because of its potential role in the adaptation of P. syringae to its specialized phytopathogenic lifestyle.

Adaptation, Physiological↗
PubMed2005

Pseudomonas syringae manipulates systemic plant defenses against pathogens and herbivores.

Many pathogens are virulent because they specifically interfere with host defense responses and therefore can proliferate. Here, we report that virulent strains of the bacterial phytopathogen Pseudomonas syringae induce systemic susceptibility to secondary P. syringae infection in the host plant Arabidopsis thaliana. This systemic induced susceptibility (SIS) is in direct contrast to the well studied avirulence/R gene-dependent resistance response known as the hypersensitive response that elicits systemic acquired resistance. We show that P. syringae-elicited SIS is caused by the production of coronatine (COR), a pathogen-derived functional and structural mimic of the phytohormone jasmonic acid (JA). These data suggest that SIS may be a consequence of the previously described mutually antagonistic interaction between the salicylic acid and JA signaling pathways. Virulent P. syringae also has the potential to induce net systemic susceptibility to herbivory by an insect (Trichoplusia ni, cabbage looper), but this susceptibility is not caused by COR. Rather, consistent with its role as a JA mimic, COR induces systemic resistance to T. ni. These data highlight the complexity of defense signaling interactions among plants, pathogens, and herbivores.

Animals↗