Identification and Characterization of an Arabidopsis Ecotype Which Fails to Mount a Hypersensitive Response When Infiltrated with Pseudomonas Syringae Strains Carrying a Vrrpt2

Abstract

Effective plant defense responses against particular pathogens often involve a one-for-one correspondence between an avirulence (avr) gene in the pathogen and a resistance gene in the host [1]. Resistance genes are thought to encode receptors that perceive signals generated by avr genes and these specific recognition events are hypothesized to trigger the host defense response, including the so-called hypersensitive response (HR), which involves localized programmed cell death in the plant host in response to infection by an avirulent pathogen. Challenge of resistant plants with high doses of avirulent pathogens results in a visible HR, characterized by formation of dry, necrotic lesions, whereas lower doses lead to an HR that is only detectable microscopically. At the molecular level, several bacterial and fungal avr genes have been cloned, and in a few cases, avrgenerated signals have been identified [2, 3]. In contrast to avr genes, until recently only a single plant resistance gene, the tomato PTO gene, corresponding to a specific avr gene, had been cloned [4]. PTO encodes a serine threonine kinase, indicating that phosphorylation occurs in the signal transduction pathway leading to the HR.