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PubMed2001

The arabidopsis ISR1 locus controlling rhizobacteria-mediated induced systemic resistance is involved in ethylene signaling.

In Arabidopsis, the rhizobacterial strain Pseudomonas fluorescens WCS417r triggers an induced systemic resistance (ISR) response that is effective against different types of pathogens. The ISR signaling pathway functions independent of salicylic acid, but requires responsiveness to jasmonate (JA) and ethylene. Using the genetic variability of ISR inducibility between Arabidopsis accessions, we recently identified a locus (ISR1) on chromosome III that is involved in ISR signaling. Accessions RLD and Wassilewskija (Ws) are recessive at the ISR1 locus and are, therefore, unable to develop ISR. Here we investigated whether the ISR1 locus is involved in JA or ethylene signaling. Compared with the ISR-inducible accession Columbia (Col), accessions RLD and Ws were not affected in JA-induced inhibition of root growth and expression of the JA-responsive gene Atvsp, suggesting that the ISR1 locus is not involved in JA signaling. However, RLD and Ws showed an affected expression of the triple response and a reduced expression of the ethylene responsive genes Hel and Pdf1.2 after exogenous application of the ethylene precursor 1-aminocyclopropane-1-carboxylate. Moreover, in contrast to Col, RLD and Ws did not develop resistance against P. syringae pv. tomato DC3000 after treatment of the leaves with 1-aminocyclopropane-1-carboxylate. Analysis of the F(2) and F(3) progeny of a cross between Col (ISR1/ISR1) and RLD (isr1/isr1) revealed that reduced sensitivity to ethylene cosegregates with the recessive alleles of the ISR1 locus. These results suggest that the ISR1 locus encodes a component of the ethylene response, which is required for the expression of rhizobacteria-mediated ISR.

Acetates↗
PubMed2001

Expression of 35S::Pto globally activates defense-related genes in tomato plants.

The tomato (Lycopersicon esculentum) resistance gene Pto confers resistance to the bacterial pathogen Pseudomonas syringae pv tomato carrying the avirulent gene avrPto. Overexpressing Pto under the control of the cauliflower mosaic virus 35S promoter constitutively activates defense responses in the absence of pathogen infection and nonspecifically enhances disease resistance. To elucidate the mechanisms underlying this resistance, we isolated cDNAs corresponding to transcripts that accumulated in 35S::Pto plants. By using suppression subtractive hybridization, we isolated 82 unique cDNA clones, most of which corresponded to differentially expressed transcripts. Most of the genes examined were also induced by pathogen inoculation. Sequence analysis showed that a large number of genes encode defense-related proteins, and most had not been previously isolated from tomato. The isolated cDNAs also include those with a putative role in the oxidative burst, proteolysis, the hypersensitive response, signal transduction, and a number of genes with unknown functions. The isolation of these cDNAs of diverse functions will assist in the characterization of defense pathways activated during disease resistance.

Bacterial Proteins↗
PubMed1969

The influence of syringomycin on ribonucleic acid synthesis.

Syringomycin, a wide-spectrum antibiotic produced by strains of Pseudomonas syringae which cause bacterial canker of peach, was able to bind to salmon sperm and calf thymus deoxyribonucleic acid but not to calf thymus histone; it also inhibited ribonucleic acid polymerase activity. These abilities to bind to deoxyribonucleic acid and to inhibit ribonucleic acid polymerase were inactivated when the phytotoxic and antibiotic properties of syringomycin were inactivated.

Animals↗
PubMed1982

Bacterial ice nucleation: a factor in frost injury to plants.

Heterogeneous ice nuclei are necessary, and the common epiphytic ice nucleation active (INA) bacteria Pseudomonas syringae van Hall and Erwinia herbicola (Löhnis) Dye are sufficient to incite frost injury to sensitive plants at -5 degrees C. The ice nucleation activity of the bacteria occurs at the same temperatures at which frost injury to sensitive plants occurs in nature. Bacterial ice nucleation on leaves can be detected at about -2 degrees C, whereas the leaves themselves, i.e. without INA bacteria, contain nuclei active only at much lower temperatures. The temperature at which injury to plants occurs is predictable on the basis of the ice nucleation activity of leaf discs, which in turn depends on the number and ice nucleation activity of their resident bacteria. Bacterial isolates which are able to incite injury to corn at -5 degrees C are always active as ice nuclei at -5 degrees C. INA bacteria incited frost injury to all of the species of sensitive plants tested.

Journal Article↗
PubMed1983

Inhibition of Glutamine Synthetase from Pea by Tabtoxinine-beta-lactam.

Tabtoxinine-beta-lactam, a hydrolytic product of tabtoxin produced by Pseudomonas syringae pv. tabaci, apparently inactivates pea seed glutamine synthetase. Inhibition of the enzyme's initial velocity is linear over a range of 0.5 to 5 millimolar tabtoxinine-beta-lactam in the presence of 10 millimolar glutamate. A method for the purification of glutamine synthetase from dried peas is presented which gives a 30% yield with a 2,000-fold increase in specific activity. A method for obtaining highly purified tabtoxinine-beta-lactam and tabtoxin in good yields is also presented. The authenticity and purity of tabtoxinine-beta-lactam and tabtoxin were verified by chromatography, biological activity, and (1)H and (13)C nuclear magnetic resonance spectroscopy.

Journal Article↗
PubMed1984

Inactivation of Glutamine Synthetase by Tabtoxinine-beta-lactam : Effects of Substrates and pH.

The inactivation of glutamine synthetase by tabtoxinine-beta-lactam, a phytotoxin produced by Pseudomonas syringae pv. tabaci, was shown to be irreversible. The chloroplast and cytosolic forms of the enzyme from pea leaves (Pisum sativum L.) were separated, purified, and found to be kinetically similar with K(m) values for glutamate of 6.7 and 4.3 millimolar and for ATP of 2.0 and 1.3 millimolar, respectively. Both forms were irreversibly inactivated by the toxin at equal rates. Using the chloroplast form, it was found that inactivation by tabtoxinine-beta-lactam required ATP. Glutamate and low levels of ammonia (<2 millimolar) slowed the rate of inactivation, whereas high levels of ammonia (5, 20, and 50 millimolar) accelerated it. The inactivation proceeded at a faster rate as the pH was increased from pH 6.5 to 7.5. The role which cellular compartmentalization could play in the inactivation is discussed.

Journal Article↗
PubMed1985

Ice nucleation temperature of individual leaves in relation to population sizes of ice nucleation active bacteria and frost injury.

Ice nucleation temperatures of individual leaves were determined by a tube nucleation test. With this assay, a direct quantitative relationship was obtained between the temperatures at which ice nucleation occurred on individual oat (Avena sativa L.) leaves and the population sizes of ice nucleation active (INA) bacteria present on those leaves. In the absence of INA bacteria, nucleation of supercooled growth-chamber grown oat leaves did not occur until temperatures were below approximately -5 degrees C. Both nucleation temperature and population size of INA bacteria were determined on the same individual, field-grown oat leaves. Leaves with higher ice nucleation temperatures harbored larger populations of INA bacteria than did leaves with lower nucleation temperatures. Log(10) mean populations of INA bacteria per leaf were 5.14 and 3.51 for leaves with nucleation temperatures of -2.5 degrees C and -3.0 degrees C, respectively. Nucleation frequencies (the ratio of ice nuclei to viable cells) of INA bacteria on leaves were lognormally distributed. Strains from two very different collections of Pseudomonas syringae and one of Erwinia herbicola were cultured on nutrient glycerol agar and tested for nucleation frequency at -5 degrees C. Nucleation frequencies of these bacterial strains were also lognormally distributed within each of the three sets. The tube nucleation test was used to determine the frequency with which individual leaves in an oat canopy harbored large populations of INA bacteria throughout the growing season. This test also predicted relative frost hazard to tomato (Lycopersicon esculentum Mill) plants.

Journal Article↗
PubMed1985

Stimulation of ethylene production in bean leaf discs by the pseudomonad phytotoxin coronatine.

Coronatine is a toxin produced by Pseudomonas syringae pv. glycinea which induces the same chlorotic response in bean leaves as does infection by the bacterial pathogen. Although the structure of coronatine is known, the biological mode of action is not. One possible clue to its activity is the ethyl-substituted cyclopropane side chain of the molecule. This part structure (1-amino-2-ethycyclopropane-1-carboxylic acid or AEC) is an analog of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC).When coronatine was applied to bean leaf discs in solution, or to intact leaves through prick application, a substantial stimulation of ethylene production was measured. This stimulation was concomitant with an increase in ACC content of the tissue, and occurred under the same conditions as did the chlorotic response to the toxin. The stimulation of ethylene production was inhibited by aminoethoxyvinylglycine, an inhibitor of ACC synthesis. These results, along with those of experiments using l-[U-(14)C]methionine, indicated that the stimulation involved de novo production of ethylene via the methionine pathway.The whole, unhydrolyzed coronatine molecule is probably necessary to elicit both the ethylene and chlorosis responses since neither hydrolysis product (coronafacic acid and coronamic acid AEC]) is effective alone. A naturally occurring analog of coronatine, coronafacoylvaline, also stimulated ethylene production and caused chlorosis. However, the unrelated pseudomonad phytotoxin phaseolotoxin, which also causes chlorosis, did not stimulate ethylene production. Ethylene thus may have a specific role in the coronatine toxic syndrome.

Journal Article↗
PubMed1985

Association between Symptom Development and Inhibition of Ornithine Carbamoyltransferase in Bean Leaves Treated with Phaseolotoxin.

The chlorosis symptom that characterizes the halo blight disease of Phaseolus vulgaris L. is caused by phaseolotoxin produced by the plant pathogenic bacterium Pseudomonas syringae pv phaseolicola. Phaseolotoxin is hydrolyzed by plant peptidases to N(delta)(N'-sulpho-diaminophosphinyl) -l-ornithine which also causes chlorosis and is reported to be an irreversible inhibitor of ornithine carbamoyltransferase (OCTase). We have examined the hypothesis that inhibition of OCTase is the primary action of phaseolotoxin that leads to chlorosis.Chlorotic spots appeared on the primary leaves of P. vulgaris seedlings during the 2 days following leaf prick application of a minimum of 30 picomole phaseolotoxin. OCTase in extracts of the lesions was reduced to 20%, or less, of the activity in controls. Four hours after the application of phaseolotoxin the concentration of free ornithine increased more than 2-fold. Other amino acids, especially glutamine and asparagine-but not arginine-increased later. Chlorophyll remained at a constant level in the phaseolotoxin-treated tissue and the appearance of chlorosis was due to the increase in chlorophyll in the surrounding unaffected tissue.Clear halo symptoms developed only on primary leaves of the youngest seedlings (treated 6-7 days after germination). Lesions did not develop on primary leaves of seedlings more than 14 days old, in which the chlorophyll concentration had reached a maximum. OCTase also was inhibited in the symptomless tissue from older leaves treated with phaseolotoxin, but there was no accumulation of amino acids, including ornithine. A single appliction of 200 nanomoles arginine resulted in the complete regreening of the chlorosis caused by phaseolotoxin. Soluble protein was lower in the chlorotic tissue than in the controls, but increased to greater than the control value following the appliction of arginine. These results suggest that phaseolotoxin-induced chlorosis results from reduced chlorophyll synthesis that is associated with arginine-starvation in the tissue where OCTase is inhibited.

Journal Article↗
PubMed1986

Secretion of Zeatin, Ribosylzeatin, and Ribosyl-1'' -Methylzeatin by Pseudomonas savastanoi: Plasmid-Coded Cytokinin Biosynthesis.

Cytokinin production by strains of the phytopathogenic bacterium Pseudomonas syringae pv savastanoi was measured by immunoaffinity chromatography of the culture medium on immobilized anti-cytokinin antibodies, followed by high performance liquid chromatography, radioimmunoassay and mass spectrometry. P. savastanoi strain PB213-2 secretes zeatin (80 nanograms per milliliter) and ribosylzeatin (80 nanograms per milliliter). Even higher levels of zeatin (400 nanograms per milliliter) are produced by the olive-specific strain EW1006, which also produces 180 nanograms per milliliter of the recently identified cytokinin, ribosyl-1'' -methylzeatin. The amounts secreted were approximately 1000 times greater than those secreted by Agrobacterium tumefaciens (DA Regier, RO Morris 1982 Biochem Biophys Res Commun 104: 1560-1566). Examination of cytokinin production by plasmid deletion mutants of PB213-2 and EW1006 indicated that cytokinin biosynthesis was specified, at least in part, by plasmid-borne genes. A fragment of the 105 kilobase pair plasmid from EW1006 was cloned into Escherichia coli where its expression resulted in dimethylallyl transferase activity and the secretion of zeatin.

Journal Article↗
PubMed1987

Tabtoxinine-beta-Lactam Transport into Cultured Corn Cells : Uptake via an Amino Acid Transport System.

Tabtoxinine-beta-lactam (T-beta-L), a unique amino acid, is a toxin produced by several closely related pathovars of Pseudomonas syringae. These chlorosis-inducing pathogens establish themselves in the apoplastic space of their hosts where they release the toxin. We have examined the transport of T-beta-L into cultured corn (Zea mays cv Black Mexican) cells using [(14)C]T-beta-L. The pH optimum of the uptake of the toxin was between 4.0 and 5.5 pH units. Toxin uptake was inhibited by the protonophore, carbonyl cyanide m-chlorophenyl hydrazone, and by the sulfhydryl re-agent, N-ethylmaleimide. Tabtoxinine-beta-lactam transport exhibited saturation kinetics that were described by the Michaelis-Menton equation for toxin concentrations of 1 millimolar and less. However, the transport of toxin in concentrations greater than 1 millimolar was not described by Michaelis-Menten kinetics. Glutamate and alanine exhibited similar transport kinetics with a transition to non-Michaelis-Menten kinetics when the amino acid concentration exceeded 1 millimolar. Hill numbers for glutamate, alanine, and T-beta-L ranged from 0.6 to 0.8. Methionine, alanine, tyrosine, glutamine, glutamate, and arginine were inhibitors of toxin transport. Alanine was a competitive inhibitor of the transport of T-beta-L and of glutamate. The data are consistent with T-beta-L being transported into the plant cell through an amino acid transport system.

Journal Article↗
PubMed1988

Development, distribution, and characteristics of intrinsic, nonbacterial ice nuclei in prunus wood.

Ice nuclei active at approximately -2 degrees C and intrinsic to woody tissues of Prunus spp. were shown to have properties distinct from bacterial ice nuclei. Soaking 5-centimeter peach stem sections in water for 4 hours lowered the mean ice nucleation temperature to below -4 degrees C, nearly 2 degrees C lower than stems inoculated with ice nucleation-active Pseudomonas syringae strain B301D. Ice nucleation activity in peach was fully restored by air-drying woody stem sections for a few hours. The ice nuclei in woody tissue were inactivated between 40 and 50 degrees C, but unaffected by treatment with bacterial ice nucleation inhibitors (i.e. NaOCl, tartaric acid, Triton XQS-20), sulfhydryl reagents (i.e. p-hydroxymercuribenzoate and iodine) and Pronase. Ice nuclei could not be dislodged from stems by sonication and were shown to be equally distributed in peach bud and internodal stem tissue on a per unit mass basis; outer and inner stem tissues were also indistinguishable in ice nucleation activity. Development of ice nuclei in immature peach and sweet cherry stems did not occur until midsummer and their formation was essentially complete by late August. Once formed the ice nuclei intrinsic to woody stems were stable and unaffected by seasonal changes in growth. The apparent physiological function of the ice nuclei is discussed in relation to supercooling and mechanisms of cold hardiness in Prunus spp.

Journal Article↗
PubMed1989

Effects of Singlet Oxygen Quenchers and pH on the Bacterially Induced Hypersensitive Reaction in Tobacco Suspension Cell Cultures.

Suspension cell cultures of Nicotiana tabacum L. inoculated with the incompatible pathogen Pseudomonas syringae pv pisi undergo a hypersensitive reaction. Addition of the singlet oxygen quencher bixin to cell suspensions had no effect on hypersensitive cell death. Addition of the singlet oxygen quencher 1,4-diazabicyclo octane (DABCO) increased the medium pH and delayed the onset of cell death. This delay was eliminated when cell suspensions were buffered, and could also be induced by increasing medium pH with KOH. Bixin and DABCO also did not suppress the hypersensitive reaction in tobacco leaves. These data do not support a role for singlet oxygen in the hypersensitive reaction. Medium pH, however, appears to be a critical factor in cell suspension cultures.

Journal Article↗
PubMed1989

Increase of chalcone synthase mRNA in pathogen-inoculated soybeans with race-specific resistance is different in leaves and roots.

Soybeans (Glycine max [L.] Merr.) respond to pathogens by producing isoflavonoid-derived phytoalexins. Chalcone synthase (CHS) is the first enzyme of the flavonoid/isoflavonoid biosynthetic pathway. We investigated changes in the steady state levels of CHS mRNA and other specific mRNAs at increasing times after inoculation in two different race-specific interactions, one between leaves and the bacterium Pseudomonas syringae pv glycinea (Psg), and one between roots and the fungus, Phytophthora megasperma f. sp. glycinea (Pmg). The amount of CHS mRNA increases significantly in soybean leaves inoculated with an avirulent race of Psg but not with a virulent race or water. In contrast, the increase in CHS mRNA is similar in roots inoculated with zoospores of either an avirulent or virulent race of Pmg. CHS mRNA increases significantly in pathogen inoculated roots but not in uninoculated controls. Hydroxyproline-rich glycoprotein (HRGP) has been observed by others to increase in wounded or pathogen-inoculated plants. We report here that HRGP mRNA levels are greater in roots inoculated with an avirulent Pmg race than with a virulent race, but inoculation with either race causes a significant increase in HRGP mRNA with respect to controls. Calmodulin or ubiquitin mRNA do not increase in either uninoculated or inoculated roots and leaves. The possibility that race-specific resistance in soybeans is expressed differently in different organs of the plant is discussed.

Journal Article↗
PubMed1990

Xylanase, a novel elicitor of pathogenesis-related proteins in tobacco, uses a non-ethylene pathway for induction.

Antisera to acidic isoforms of pathogenesis-related proteins were used to measure the induction of these proteins in tobacco (Nicotiana tabacum) leaves. Endo-(1-4)-beta-xylanase purified from culture filtrates of Trichoderma viride was a strong elicitor of pathogenesis-related protein synthesis in tobacco leaves. The synthesis of these proteins was localized to tissue at the area of enzyme application. The inhibitors of ethylene biosynthesis and ethylene action, 1-aminoethoxyvinylglycine and silver thiosulfate, inhibited accumulation of pathogenesis-related proteins induced by tobacco mosaic virus and alpha-aminobutyric acid, but did not inhibit elicitation by xylanase. Likewise, the induction of these proteins by the tobacco pathogen Pseudomonas syringae pv. tabaci was not affected by the inhibitors of ethylene biosynthesis and action. The leaf response to tobacco mosaic virus and alpha-aminobutyric acid was dependent on light in normal and photosynthetically incompetent leaves. In contrast, the response of leaves to xylanase was independent of light. Tobacco mosaic virus and alpha-aminobutyric acid induced concerted accumulation of pathogenesis-related proteins. However, xylanase elicited the accumulation of only a subset of these proteins. Specifically, the plant (1-3)-beta-glucanases, which are normally a part of the concerted response, were underrepresented. These experiments have revealed the presence of a novel ethylene-independent pathway for pathogenesis-related protein induction that is activated by xylanase.

Journal Article↗
PubMed1991

Rapid identification of cytokinins by an immunological method.

A method for rapid identification of bacterial cytokinins has been developed in which cultures are fed [(3)H]adenine, the cytokinins (including (3)H-labeled cytokinins) are isolated by immunoaffinity chromatography, and analyzed by HPLC with on-line scintillation counting. Analysis of Agrobacterium tumefaciens strains showed that some produced primarily trans-zeatin, whereas others produced primarily trans-zeatin riboside. Pseudomonas syringae pv savastanoi produced mixtures of trans-zeatin, dihydrozeatin, 1''-methyl-trans-zeatin riboside, and other unknown cytokinin-like substances. Corynebacterium fascians, produced cis-zeatin, isopentenyladenine and isopentenyladenosine. The technique is designed for qualitative rather than quantitative studies and allows ready identification of bacterial cytokinins. It may also have utility in the study of plant cytokinins if adequate incorporation of label into cytokinin precursor pools can be achieved.

Journal Article↗
PubMed1991

Use of Dimethyl Sulfoxide to Detect Hydroxyl Radical during Bacteria-Induced Hypersensitive Reaction.

Excess active oxygen is generated during the hypersensitive reaction (HR), an incompatible reaction of plants to bacterial pathogens. During HR, lipid peroxidation correlates chronologically with production of the oxygen species, superoxide (O(2) (.-)). However, O(2) (.-) may not be the active oxygen species that initiates lipid peroxidation. Evidence from other systems suggest that O(2) (.-) is converted to the hydroxyl radical (HO(.)) before lipid peroxidation is initiated. Until recently, HO(.) could not be detected directly in vivo. This study utilizes a newly reported method to directly detect and quantify the formation of HO(.)in vivo. Dimethyl sulfoxide (DMSO), used as a molecular probe, is oxidized by HO(.), forming the stable compound methanesulfinic acid. The methanesulfinic acid can be easily extracted from plant tissues and measured with a colorimetric assay. This study demonstrates significant increases in HO(.) concentration after simultaneous infiltration of cucumber (Cucumis sativa L.) plants with paraquat and DMSO. The concentration of HO(.) did not increase significantly when cucumber plants were infiltrated simultaneously with the HR-inducing bacteria, Pseudomonas syringae pv. pisi, and with DMSO. Lipid peroxidation, however, could be measured at times when HO(.) was not detectable. It appears that HO(.) is not generated during bacteria-induced HR; therefore, HO(.) is not responsible for the initiation of lipid peroxidation.

Journal Article↗
PubMed2002

Tomato transcription factors pti4, pti5, and pti6 activate defense responses when expressed in Arabidopsis.

The Pti4, Pti5, and Pti6 proteins from tomato were identified based on their interaction with the product of the Pto disease resistance gene, a Ser-Thr protein kinase. They belong to the ethylene-response factor (ERF) family of plant-unique transcription factors and bind specifically to the GCC-box cis element present in the promoters of many pathogenesis-related (PR) genes. Here, we show that these tomato ERFs are localized to the nucleus and function in vivo as transcription activators that regulate the expression of GCC box-containing PR genes. Expression of Pti4, Pti5, or Pti6 in Arabidopsis activated the expression of the salicylic acid-regulated genes PR1 and PR2. Expression of jasmonic acid- and ethylene-regulated genes, such as PR3, PR4, PDF1.2, and Thi2.1, was affected differently by each of the three tomato ERFs, with Arabidopsis-Pti4 plants having very high levels of PDF1.2 transcripts. Exogenous application of salicylic acid to Arabidopsis-Pti4 plants suppressed the increased expression of PDF1.2 but further stimulated PR1 expression. Arabidopsis plants expressing Pti4 displayed increased resistance to the fungal pathogen Erysiphe orontii and increased tolerance to the bacterial pathogen Pseudomonas syringae pv tomato. These results indicate that Pti4, Pti5, and Pti6 activate the expression of a wide array of PR genes and play important and distinct roles in plant defense.

Arabidopsis↗