Harpin, Elicitor of the Hypersensitive Response Produced by the Plant Pathogen
            <i>Erwinia amylovora</i>

Wei, Zhong-Min; Laby, Ron J.; Zumoff, C. H.; Bauer, Dierk; He, Sheng Yang; Collmer, Alan; Beer, Steven V.

doi:10.1126/science.1621099

Cited by 712 publications

(588 citation statements)

References 16 publications

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“…The OGA preparation used in these studies contained 0.5 mg/ml galacturonic equivalents as determined by the method of Blumenkrantz and Asboe-Hansen (41). Harpin, a potent inducer of both the oxidative burst (11,12) and the hypersensitive response (42), was a kind gift of Dr. Steven Beer (Cornell University). Mas-7, an active analog of mastoparan, and Mas-17, its inactive counterpart, were purchased from Calbiochem.…”

Section: Methodsmentioning

confidence: 99%

“…a pathway commonly inaugurated by Ca 2ϩ channels (47). Finally, harpin, a heat stable protein from the bacteria E. amylovora was chosen, because it induces the oxidative burst (11,12) and may promote the hypersensitive response (42,48) in tobacco. Importantly, in addition to serving as potent inducers of the oxidative burst, all of the above elicitors are available in relatively pure form, confirming that any Ca 2ϩ transients observed will have been induced by the same component in the preparation that is responsible for stimulating the oxidative burst.…”

Section: Some Elicitors Of the Oxidative Burst Induce A Ca 2ϩmentioning

confidence: 99%

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Measurement of Ca2+ Fluxes during Elicitation of the Oxidative Burst in Aequorin-transformed Tobacco Cells

Chandra

Low

1997

Journal of Biological Chemistry

146

117

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We have employed suspension cultured aequorintransformed tobacco cells to examine the involvement of Ca 2؉ in signal transduction of the oxidative burst. Use of cultured cells for this purpose was validated by demonstrating that the cells responded to cold shock quantitatively and qualitatively similarly to the intact transgenic plants from which they were derived. Stimulation of the oxidative burst in the cell suspension was achieved by administration of oligogalacturonic acid, Mas-7 (a peptide known to activate G proteins and Ca 2؉ fluxes), hypo-osmotic stress, or harpin (a protein from the pathogenic bacterium Erwinia amylovora). The latter failed to promote any detectable increase in cytoplasmic Ca 2؉ concentration, whereas each of the former three triggered a rapid rise in cytosolic Ca 2؉ followed by a return within seconds to basal Ca 2؉ levels. Peak Ca 2؉ concentrations induced by the former three elicitors were ϳ0.7, 1.4, and 1.3 M, respectively. Three lines of evidence suggest that the observed Ca 2؉ pulses are essential to transduction of the oxidative burst signals by their respective elicitors: (i) inhibition of the Ca 2؉ transients with Ca 2؉ chelators or Ca 2؉ channel blockers prevented expression of the oxidative burst, (ii) introduction of exogenous Ca 2؉ into the same cells initiated the burst even in the absence of other inducers of the response, and (iii) the observed Ca 2؉ transients often returned to near basal levels well before any H 2 O 2 synthesis could be detected, suggesting that the Ca 2؉ influx is required to communicate the burst signal but not maintain the defense response. These data suggest that Ca 2؉ pulses serve frequently, but not invariably, to transduce an oxidative burst signal.The oxidative burst constitutes one of the more rapid responses of a plant cell to pathogen attack (1). Within minutes of pathogen recognition, reactive oxygen species are generated that may promote cross-linking and lignification of the cell wall (2, 3), transcription of defense-related genes (4, 5), secondary metabolite biosynthesis (6), the hypersensitive response (4,7,8), and direct pathogen cytotoxicity (9, 10), depending on the plant species examined. In cultured cell systems, the oxidative burst can be promoted by isolated elicitors including harpin (11, 12), oligouronides (13), elicitins (14), purified fungal peptides (15), and other molecules from the extracts of pathogens (7,16). Abiotic stimuli such as mechanical stress (17), the pesticide fenthion (18), cold shock (19), phosphatase inhibitors (4, 20), and hypo-osmotic stress (17) can also induce biosynthesis of reactive oxygen species in plant cells.Because of its rapid expression, ease of assay, and similarity to the analogous defense response in human neutrophils (21), the oxidative burst has recently served as a model for exploring signal transduction pathways in plants. As the numbers of elicitors examined have risen, it has become increasingly clear that different elicitors may inaugurate independent signal transduction pathways that...

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Section: Methodsmentioning

confidence: 99%

Section: Some Elicitors Of the Oxidative Burst Induce A Ca 2ϩmentioning

confidence: 99%

Measurement of Ca2+ Fluxes during Elicitation of the Oxidative Burst in Aequorin-transformed Tobacco Cells

Chandra

Low

1997

Journal of Biological Chemistry

146

117

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“…Kieffer et al [54] demonstrated the possible involve- shown to induce AOS production and K + /H + exchange in a tobacco cell-suspension system [55]. Harpin has been shown to elicit the hypersensitive response in tobacco and other non-host species [56,57]. Harpins are capable of inducing systemic acquired resistance that protects plants against multiple diseases and even insects [25][26][27].…”

Section: Cell Culture Experimentsmentioning

confidence: 99%

Induction of defense responses in tobacco by the protein Nep1 from Fusarium oxysporum

et al. 2001

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“…Mutants that lack the synthesis of levan were reduced in virulence (24), and mutants deficient in amylovoran synthesis were nonpathogenic (4,9). The precise role of EPS in the infection process is still unknown, and genetic analysis revealed additional factors which are involved in virulence of the pathogen (40,52). The capsule of amylovoran (5) may protect the bacteria from recognition by plant defense mechanisms after masking cell surface components (34).…”

mentioning

confidence: 99%

Characterization of the rcsB gene from Erwinia amylovora and its influence on exoploysaccharide synthesis and virulence of the fire blight pathogen

Bereswill

Geider

1997

J Bacteriol

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RcsB belongs to a family of positive regulators of exopolysaccharide synthesis in various enterobacteria. The rcsB gene of the fire blight pathogen Erwinia amylovora was cloned by PCR amplification with consensus primers, and its role in exopolysaccharide (EPS) synthesis was investigated. Its overexpression from highcopy-number plasmids stimulated the synthesis of the acidic EPS amylovoran and suppressed expression of the levan-forming enzyme levansucrase. Inactivation of rcsB by site-directed mutagenesis created mutants that were deficient in amylovoran synthesis and avirulent on host plants. In addition, a cosmid which complemented rcsB mutants was selected from a genomic library. The spontaneous E. amylovora mutant E8 has a similar phenotype and was complemented by the cloned rcsB gene. The rcsB region of strain E8 was also amplified by PCR, and the mutation was characterized as a nine-nucleotide deletion at the start of the rcsB gene. Nucleotide sequence analysis of the E. amylovora rcsB region and the predicted amino acid sequence of RcsB revealed extensive homology to rcsB and the encoded protein of other bacteria such as Escherichia coli and Erwinia stewartii. In all three organisms, rcsB is localized adjacent to the rcsC gene, which is transcribed in the opposite direction of rcsB. The E. amylovora rcsB gene has now been shown to strongly affect the formation of disease symptoms of a plant pathogen.The gram-negative bacterium Erwinia amylovora causes fire blight on rosaceous plants. Typical symptoms are wilting, necrotic lesions, and production of ooze which consists mainly of capsular exopolysaccharide (EPS) produced by the bacteria. Production of capsule polysaccharides is a common feature of many gram-negative bacteria (49), especially plant pathogens (32). The capsule creates a favorable microenvironment for the bacterial cells and protects them against water stress and plant defense mechanisms. E. amylovora produces two types of EPS, amylovoran and levan (2). Levan is a neutral homopolymer composed of ␤-2,6-linked fructose molecules, and its synthesis is mediated by the enzyme levansucrase. Levansucrase is secreted into the environment and uses sucrose as a substrate (29). The levansucrase gene (lsc) of E. amylovora was recently cloned and characterized and was found to be constitutively expressed by the pathogen (24). Amylovoran is an acidic heteropolymer composed of a pentasaccharide repeating unit that contains four galactose molecules and one glucuronic acid residue (35,45). Its synthesis is encoded by the ams (for amylovoran synthesis) operon, which was also cloned and sequenced (13). The 12 genes amsA to amsL are organized in a large gene cluster on the bacterial chromosome. Transposonand site-directed mutagenesis of the lsc gene and the ams operon revealed that both types of EPS are important for the virulence of E. amylovora. Mutants that lack the synthesis of levan were reduced in virulence (24), and mutants deficient in amylovoran synthesis were nonpathogenic (4, 9). The precise role of EP...

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Harpin, Elicitor of the Hypersensitive Response Produced by the Plant Pathogen Erwinia amylovora

Cited by 712 publications

References 16 publications

Measurement of Ca2+ Fluxes during Elicitation of the Oxidative Burst in Aequorin-transformed Tobacco Cells

Measurement of Ca2+ Fluxes during Elicitation of the Oxidative Burst in Aequorin-transformed Tobacco Cells

Induction of defense responses in tobacco by the protein Nep1 from Fusarium oxysporum

Characterization of the rcsB gene from Erwinia amylovora and its influence on exoploysaccharide synthesis and virulence of the fire blight pathogen

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