Ethylene promotes the necrotic lesion formation and basic PR gene expression in TMV-infected tobacco

Ethylene has been thought to be an important factor for the induction of defense responses against pathogen attack, bat its function in these responses has not been well defined. Here we show the direct involvement of ethylene in the formation of necrotic lesions and in basic pathogenesis-related (PR) protein gene induction in tobacco. Increase in ethylene production as well as accumulation of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) gene transcript obviously preceded the lesion appearance in tobacco mosaic virus (TMV)-infected leaves in an N gene-dependent synchronous lesion formation system. Inhibitors of ethylene biosynthesis or action significantly suppressed both lesion formation and basic PR gene expression. Induction of these genes was enhanced in 1-aminocyclopropane-1-carboxylic acid (ACC)-treated leaves especially in ACO-overexpressing transgenic tobacco plants. Further, we found that ethylene production during hypersensitive reaction is restricted at the level of ACO activity.