Identification of tobacco ESTs with a hypersensitive response (HR)-specific pattern of expression and likely involved in the induction of the HR and/or localized acquired resistance (LAR)1

Plant defense responses against pathogens often involve the restriction of the pathogen to its site of penetration. Restriction is achieved through the combined effects of the hypersensitive response (HR) and its tightly connected localized acquired resistance (LAR). As LAR is induced by unknown signals released by the cells undergoing the HR, LAR inducing/regulating genes must show a HR-specific pattern of expression. Here, we describe a differential display reverse-transcript polymerase chain reaction (DDRT-PCR) strategy to isolate tobacco expressed sequence tags (ESTs) characterized by such an expression profile, which also characterizes genes involved in the induction/execution of the HR. We compared the DDRT-PCR profile of tobacco cell suspensions treated with β-megaspermin inducing the HR with that of untreated cells and cells treated with α-megaspermin inducing a Defense No Death (DND) phenotype. The expression profile of the selected ESTs was analyzed in tobacco plants expressing a β-megaspermin-induced HR or a DND phenotype, including LAR, induced by three different elicitors. This comprehensive analysis allowed to identify 24 HR-specific ESTs, half of them shows no or non-significant homology with ESTs and genes in the databases. The other half exhibits homology with genes encoding a receptor-like kinase protein, proteins involved in the regulation of plasma membrane structure, proteins of the ubiquitin/26S proteasome proteolytic system, RNA binding proteins, and a protein hypothesized to be a true regulator of the HR.