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PubMed2003

Purification and characterization of a phytase from Pseudomonas syringae MOK1.

A phytase (EC 3.1.3.8) from Pseudomonas syringae MOK1 was purified to apparent homogeneity in two steps employing cation and an anion exchange chromatography. The molecular weight of the purified enzyme was estimated to be 45 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The optimal activity occurred at pH 5.5 and 40 degrees C. The Michaelis constant (Km) and maximum reaction rate (Vmax) for sodium phytate were 0.38 mM and 769 U/mg of protein, respectively. The enzyme was strongly inhibited by Cu2+, Cd2+, Mn2+, and ethylenediaminetetraacetic acid (EDTA). It showed a high substrate specificity for sodium phytate with little or no activity on other phosphate conjugates. The enzyme efficiently released orthophosphate from wheat bran and soybean meal.

6-Phytase↗
PubMed2005

Molecular cloning of a phytase gene (phy M) from Pseudomonas syringae MOK1.

A phytase gene (phy M) was cloned from Pseudomonas syringae MOK1 by two steps of degenerate PCR and inverse PCR. This gene consists of 1,287 nucleotides and encodes a polypeptide of 428 amino acids with a deduced molecular mass of 46,652 kDa. Based on its amino acid sequence, the Phy M shares the active site RHGXRXP and HD sequence motifs, typically characterized by histidine acid phosphatases familly. Each phy M gene fragment encoding mature Phy M with its own signal sequence (pEPSS) and without (pEPSM) was subcloned into the E. coli BL21 (DE3) expression vector, pET22b (+). The enzyme activity in crude extracts of clone pEPSM was 2.514 Umg(-1) of protein, and about 10-fold higher than that of clone pEPSS.

6-Phytase↗
PubMed2003

Induction of 3'-O-beta-D-ribofuranosyl adenosine during compatible, but not during incompatible, interactions of Arabidopsis thaliana or Lycopersicon esculentum with Pseudomonas syringae pathovar tomato.

All hitherto identified aromatic compounds accumulating in leaves of Arabidopsis thaliana (L.) Heynh. upon infection with virulent or avirulent strains of Pseudomonas syringae pathovar tomato ( Pst) were indolic metabolites. We now report the strong accumulation of a novel type of natural product, 3'-O-beta-D-ribofuranosyl adenosine (3'RA), exclusively during compatible interactions. In contrast to the various indolic metabolites, 3'RA was undetectable in incompatible interactions of A. thaliana leaves with an avirulent Pst strain, as well as in uninfected control leaves. A similar, strong induction of 3'RA was observed in compatible but, again, not in incompatible interactions of Pst with its natural host, Lycopersicon esculentum. The strength of the effect and its confinement to compatible interactions suggests that it may be applicable as a diagnostic tool.

Adenosine↗
PubMed2004

Fusicoccin activates pathogen-responsive gene expression independently of common resistance signalling pathways, but increases disease symptoms in Pseudomonas syringae-infected tomato plants.

Fusicoccin (FC), an activator of the plant plasma membrane H+-ATPase, induces several components of plant pathogen resistance responses, including defence hormone biosynthesis and pathogenesis-related (PR) gene expression. The mechanism by which these responses occur, and the effect they have on plant-pathogen interactions is unknown. Here, we show that PR gene expression in response to FC in tomato (Lycopersicon esculentum Mill.) plants does not strictly require the common defence hormones, salicylic acid, jasmonic acid and ethylene. We also show that FC-induced PR gene expression requires neither Ca2+ nor reactive oxygen species, typical early pathogen-resistance response signals. The possibility that PR gene expression is related to FC-induced dehydration stress is also discounted. Finally, we show that the defence responses elicited by FC in tomato are not sufficient to confer resistance to the bacterial pathogen Pseudomonas syringae. Rather, FC increases the rate and severity of disease symptom formation in an ethylene-dependent manner.

Gene Expression↗
PubMed2006

Infection with virulent and avirulent P. syringae strains differentially affects photosynthesis and sink metabolism in Arabidopsis leaves.

Infection of plants with pathogens leads not only to the induction of defence reactions but also to changes in carbohydrate metabolism. In this study, the effects of infection by a virulent and an avirulent strain of P. syringae on spatio-temporal changes in photosynthesis were compared using chlorophyll fluorescence imaging. The maximum PSII quantum yield, effective PSII quantum yield and nonphotochemical quenching were decreased in Arabidopsis leaves infected with either strain. At the same time, the quantum yield of nonregulated energy dissipation was increased. These changes could be detected by chlorophyll fluorescence imaging before symptoms were visible by eye. The effects were restricted to the vicinity of the infection site and did not spread to uninfected areas of the leaf. Qualitatively similar changes in photosynthetic parameters were observed in both interactions. Major differences between the responses to both strains were evident in the onset and time course of changes. A decrease in photosynthesis was detectable already at 3 h only after challenge with the avirulent strain while after 48 h the rate of photosynthesis was lower with the virulent strain. In contrast to photosynthesis, the regulation of marker genes for source/sink relations and the activities of invertase isoenzymes showed qualitative differences between both interactions. Inoculation of the virulent but not the avirulent strain resulted in downregulation of photosynthetic genes and upregulation of vacuolar invertases. The activity of vacuolar invertases transiently increased upon infection with the virulent strain but decreased with the avirulent strain while extracellular invertase activity was downregulated in both interactions.

Arabidopsis↗
PubMed2007

Case study of combinatorial imaging: what protocol and what chlorophyll fluorescence image to use when visualizing infection of Arabidopsis thaliana by Pseudomonas syringae?

Localized infection of a plant can be mapped by a sequence of images capturing chlorophyll fluorescence transients in actinic light. Choice of the actinic light protocol co-determines fluorescence contrast between infected leaf segment and surrounding healthy tissue. Frequently, biology cannot predict with which irradiance protocol, in which fluorescence image of the sequence, and in which segment of the image there will be the highest contrast between the healthy and infected tissue. Here, we introduce a new technique that can be applied to identify the combination of chlorophyll fluorescence images yielding the highest contrast. The sets of the most contrasting images vary throughout the progress of the infection. Such specific image sets, stress-revealing fluorescence signatures, can be found for the initial and late phases of the infection. Using these signatures, images can be divided into segments that show tissue in different infection phases. We demonstrate the capacity of the algorithm in an investigation of infection of the model plant Arabidopsis thaliana by the bacterium Pseudomonas syringae. We show that the highest contrast is found with transients elicited by fluctuating, harmonically modulated irradiance with long periods.

Arabidopsis↗
PubMed2004

A concise synthesis of two isomeric pentasaccharides, the O repeat units from the lipopolysaccharides of P. syringae pv. porri NCPPB 3364T and NCPPB 3365.

A concise synthesis of two isomeric pentasaccharides, alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->3)-[beta-D-GlcpNAc-(1-->2)]-alpha-L-Rhap (A) and alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->3)-[beta-D-GlcpNAc-(1-->2)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap (B), the O repeats from the lipopolysaccharides of Pseudonomonas syringae pv. porri NCPPB 3364T and 3365 was achieved via assembly of the building blocks, allyl 3,4-di-O-benzoyl-alpha-L-rhamnopyranoside (1), 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (2), allyl 4-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranoside (6), 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate (7), and allyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (10). Coupling of 1 with 2 followed by deallylation and trichloroacetimidate formation gave the disaccharide donor 5, while condensation of 6 with 7, followed by dechloroacetylation, offered the disaccharide acceptor 9. Then, 5 was coupled with 10 to obtain the trisaccharide 11, and subsequent deallylation and trichloroacetimidate formation furnished the trisaccharide donor 13. Coupling of 9 with 13, followed by deprotection, afforded pentasaccharide 19, while condensation of 9 with 5, followed by deallylation and trichloroacetimidate formation, gave the tetrasaccharide donor 16, whose coupling with 10 and subsequent deprotection yielded another pentasaccharide 22.

Carbohydrate Sequence↗
PubMed2005

Two Pseudomonas syringae type III effectors inhibit RIN4-regulated basal defense in Arabidopsis.

Plant cells have two defense systems that detect bacterial pathogens. One is a basal defense system that recognizes complex pathogen-associated molecular patterns (PAMPs). A second system uses disease-resistance (R) proteins to recognize type lll effector proteins that are delivered into the plant cell by the pathogen's type III secretion system. Here we show that these two pathways are linked. We find that two Pseudomonas syringae type III effectors, AvrRpt2 and AvrRpm1, inhibit PAMP-induced signaling and thus compromise the host's basal defense system. RIN4 is an Arabidopsis protein targeted by AvrRpt2 and AvrRpm1 for degradation and phosphorylation, respectively. We find that RIN4 is itself a regulator of PAMP signaling. The R proteins, RPS2 and RPM1, sense type III effector-induced perturbations of RIN4. Thus, R proteins guard the plant against type III effectors that inhibit PAMP signaling and provide a mechanistic link between the two plant defense systems.

Arabidopsis↗
PubMed2006

Transcript stabilization by mRNA sequences from hrpA of Pseudomonas syringae.

Production of heterologous proteins in bacteria is one of the main applications of biotechnology. Although several high-efficiency expression systems have been developed, different steps in protein production may become rate-limiting depending on the production system and the protein being produced. One bottle neck can be the instability of the mRNA. We have used fragments of the unusually long-living mRNA hrpA from the plant pathogenic bacteria Pseudomonas syringae pathovars tomato and phaseolicola to increase the half-lives of heterologous transcripts. The stabilizing effect was extended to Escherichia coli, as half-lives of several heterologous transcripts were increased from a few minutes to up to 19min. Production of heterologous proteins was also increased manifold by the addition of the stabilizing hrpA elements. We have mapped the regions of the hrpA transcript necessary and sufficient for the stabilization process.

Bacterial Proteins↗
PubMed2005

Suppression of host defense in compatible plant-Pseudomonas syringae interactions.

Despite impressive advances in the study of plant resistance to pathogens, little is known about the molecular basis of plant susceptibility to virulent pathogens. Recent progress in susceptible plant-Pseudomonas syringae interactions has provided a glimpse into the battles fought between plants and bacterial pathogens. A key step for pathogenesis appears to be the suppression of host defenses. Suppression of host defenses, including basal defense, gene-for-gene resistance and nonhost resistance, is a key step for pathogenesis. Defense suppression is mediated by bacterial effector proteins, which are secreted through the type III secretion system, and by coronatine, a bacterial toxin that structurally and functionally mimics methyl jasmonate, a plant defense signaling molecule.

Gene Expression Regulation, Plant↗
PubMed2004

The VirPphA/AvrPtoB family of type III effectors in Pseudomonas syringae.

The VirPphA/AvrPtoB family of type III effector proteins from the phytopathogenic bacterium Pseudomonas syringae is one of the models providing insights into the molecular mechanisms conferring plant disease resistance and pathogenesis. In this review we summarize recent advances concerning the VirPphA/AvrPtoB family of effectors involved in the elicitation and suppression of plant defense responses.

Amino Acid Sequence↗
PubMed2006

Steryl esters and phenylethanol esters from Syringa komarowii.

Three new steryl esters and a new phenylethanol ester, together with 22 known compounds were isolated from the aqueous ethanolic extract of the whole plants of Syringa komarowii. The new compounds were elucidated as stigmastane-3beta,6alpha-diol 3-O-tetradecanoate (1), stigmastane-3beta,6alpha-diol 3-O-palmitate (2), stigmastane-3beta,6alpha-diol 3-O-stearate (3), and 2-(4-hydroxyphenyl)-ethyl dotriacontanoate (4) on the basis of extensive spectral data and chemical evidences.

Esters↗
PubMed2004

Crystal structure of the type III effector AvrB from Pseudomonas syringae.

AvrB is a Pseudomonas syringae type III effector protein that is translocated into host plant cells during attempted pathogenesis. Arabidopsis harboring the corresponding resistance protein RPM1 can detect AvrB and mount a rapid host defense response, thus avoiding active infection. In the plant cell, AvrB induces phosphorylation of RIN4, a key component in AvrB/RPM1 recognition. Although the AvrB/RPM1 system is among the best characterized of the numerous bacterial effector/plant resistance protein systems involved in plant disease resistance and pathogenesis, the details of the molecular recognition mechanism are still unclear. To gain further insights, the crystal structure of AvrB was determined. The 2.2 A structure exhibits a novel mixed alpha/beta bilobal fold. Aided by the structural information, we demonstrate that one lobe is the determinant of AvrB/RPM1 recognition specificity. This structural information and preliminary structure-function studies provide a framework for the future understanding of AvrB function on the molecular level.

Amino Acid Sequence↗
PubMed2005

CopC protein from Pseudomonas syringae: intermolecular transfer of copper from both the copper(I) and copper(II) sites.

The CopC protein from Pseudomonas syringae pathovar tomato is expressed as one of four proteins encoded by the operon CopABCD that is responsible for copper resistance. It is a small soluble molecule (10.5 kDa) with a beta-barrel structure and features two distinct copper binding sites, which are highly specific for Cu(I) (K(D) > or = 10(-)(13)) and Cu(II) (K(D) approximately 10(-)(15)). These dissociation constants were estimated via ligand competition experiments monitored by electronic spectral and fluorescence probes. The chemistries of the two copper sites are interdependent. When the Cu(II) site is empty, the Cu(I) ion is oxidized by air, but when both sites are occupied, the molecule is stable in air. The availability of an unoccupied site of higher affinity induces intermolecular transfer of either Cu(I) or Cu(II) while maintaining free copper ion concentrations in solution at sub-picomolar levels. This intriguing copper chemistry is consistent with the proposed role of CopC as a copper carrier in the oxidizing periplasmic space. These properties would allow it to exchange either Cu(I) or Cu(II) with its putative partners CopA, CopB, and CopD, contrasting with the role of the Cu(I) (only) chaperones found in the reducing cytoplasm.

Bacterial Proteins↗
PubMed2006

Intermolecular transfer of copper ions from the CopC protein of Pseudomonas syringae. Crystal structures of fully loaded Cu(I)Cu(II) forms.

CopC is a small soluble protein expressed in the periplasm of Pseudomonas syringae pathovar tomato as part of its copper resistance response (cop operon). Equilibrium competition reactions confirmed two separated binding sites with high affinities for Cu(I) (10(-7) > or = K(D) > or = 10(-13) M) and Cu(II) (K(D) = 10(-13(1)) M), respectively. While Cu(I)-CopC was converted cleanly by O2 to Cu(II)-CopC, the fully loaded form Cu(I)Cu(II)-CopC was stable in air. Variant forms H1F and H91F exhibited a lower affinity for Cu(II) than does the wild-type protein while variant E27G exhibited a higher affinity. Cation exchange chromatography detected each of the four different types of intermolecular copper transfer reactions possible between wild type and variant forms: Cu(I) site to Cu(II) site; Cu(II) site to Cu(I) site; Cu(I) site to Cu(I) site; Cu(II) site to Cu(II) site. The availability of an unoccupied site of higher affinity induced intermolecular transfer of either Cu(I) or Cu(II) in the presence of O2 while buffering concentrations of cupric ion at sub-picomolar levels. Crystal structures of two crystal forms of wild-type Cu(I)Cu(II)-CopC and of the apo-H91F variant demonstrate that the core structures of the molecules in the three crystal forms are conserved. However, the conformations of the amino terminus (a Cu(II) ligand) and the two copper-binding loops (at each end of the molecule) differ significantly, providing the structural lability needed to allow transfer of copper between partners, with or without change of oxidation state. CopC has the potential to interact directly with each of the four cop proteins coexpressed to the periplasm.

Bacterial Proteins↗
PubMed2003

Biogenetic studies in Syringa vulgaris L.: synthesis and bioconversion of deuterium-labeled precursors into lilac aldehydes and lilac alcohols.

Syringa vulgaris L. inflorescences were fed with aqueous solutions of regioselectively deuterated compounds assumed to be precursors of lilac aldehyde and lilac alcohol, respectively. Volatiles were extracted by stir bar sorptive extraction (SBSE) and analyzed using enantioselective multidimensional gas chromatography/mass spectrometry (enantio-MDGC/MS); deuterium-labeled lilac aldehydes and lilac alcohols were separated from unlabeled stereoisomers on a fused silica capillary column, coated with heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin (DIME-beta-CD) (30%) in SE 52 (70%), as the chiral stationary phase. Feeding experiments with [5,5-(2)H(2)]mevalonic acid lactone 22 and [5,5-(2)H(2)]deoxy-d-xylose 23 indicate that the novel mevalonate independent 1-deoxy-d-xylose 5-phosphate/2C-methyl-d-erythritol 4-phosphate pathway is the dominant metabolic route for biosynthesis in lilac flowers. Additionally, bioconversion of deuterium-labeled d(5)-(R/S)-linalool 3, d(6)-(R)-linalool 21, d(5)-(R/S)-8-hydroxylinalool 6, d(5)-(R/S)-8-oxolinalool 7, d(5)-lilac aldehydes 8-11 and d(5)-lilac alcohols 12-15 into lilac during in vivo feeding experiments was investigated and the metabolic pathway is discussed. Incubation of petals with an aqueous solution of deuterated d(5)-(R/S)-linalool 3 indicates an autonomic terpene biosynthesis of lilac flavor compounds in the flower petals of lilac.

Acyclic Monoterpenes↗
PubMed2003

Biogenetic studies in Syringa vulgaris L.: bioconversion of (18)O(2H)-labeled precursors into lilac aldehydes and lilac alcohols.

Syringa vulgaris L. inflorescences, petals, and chloroplasts, isolated from lilac flower petals, were fed with aqueous solutions of (18)O-labeled linalool and [5,5-(2)H(2)]-deoxy-d-xylose (DOX). The chloroplasts of lilac flower petals were isolated after feeding experiments with labeled precursors. Volatiles from the chloroplasts were extracted by stir bar sorptive extraction (SBSE) and analyzed using enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS). Feeding experiments with DOX indicate that the novel mevalonate-independent 1-deoxy-d-xylose 5-phosphate/2C-methyl-d-erythritol 4-phosphate (DOX/MEP) is the decisive pathway of lilac aldehyde and lilac alcohol, respectively. Bioconversion of [(18)O]linalool into lilac aldehyde and lilac alcohol during in vivo feeding experiments was monitored, and the metabolic pathways are discussed.

Acyclic Monoterpenes↗