Expression of the Pseudomonas syringae avirulence protein AvrB in plant cells alleviates its dependence on the hypersensitive response and pathogenicity (Hrp) secretion system in eliciting genotype-specific hypersensitive cell death

Suresh Gopalan, David W. Bauer, James R. Alfano, Amy O. Loniello, Sheng Yang He, Alan Collmer

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196 Scopus citations


The nonpathogenic bacteria Pseudomonas fluorescens and Escherichia coli can elicit a genotype-specific hypersensitive response (HR) in plants if they express both the HR and pathogenesis (Hrp) protein secretion system and the HrpZ harpin from R syringae pv syringae 61 and a R syringae avirulence (avr) gene whose presence is recognized by a corresponding disease resistance gene in the plant. We have found that the recognition event appears to require transfer of the Avr protein into the plant cell. Elicitation of a genotype-specific HR was observed with avrB+ P. fluorescens in soybean and Arabidopsia plants carrying resistance genes RPG1 and RPM1, respectively, end with avrPto+ E. coli in tomato plants carrying resistance gene PTO, but only if the Hrp secretion system, HrpZ, and the appropriate Avr proteins were produced in the same bacterial cell. The failure of avrB hyperexpression end exogenous AvrB or HrpZ to alleviate these requirements in soybean and Arabidopsis suggests that the site of AvrB action is not in the bacterial cell or plant apoplast. An Arabidopsis rps3 (rpm1) glabrous1 mutant was transformed with constructs expressing avrB and was crossed with an Arabidopsis ecotype Columbia (RPM1 GLABROUS1) plant. F1 seedlings (identified by their kanamycin-resistant, pubescent phenotype) exhibited extensive necrosis on cotyledon leaves 10 days postgermination. Ecotype Columbia and rps3.1 leaves biolistically cobombarded with plasmids expressing the β-glucurenidase (GUS) gene and avrB failed to produce GUS activity (Indicative of cell death) only when RPM1 and avrB were present in the leaf. Thus, both stable and transient expression of avrB in Arabidopsis resulted in RPM1-dependent necrosis, and the only demonstrable site of action for AvrB was inside plant cells.

Original languageEnglish (US)
Pages (from-to)1095-1105
Number of pages11
JournalPlant Cell
Issue number7
Publication statusPublished - Jul 1 1996


ASJC Scopus subject areas

  • Plant Science
  • Cell Biology

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