Gene-for-gene specificity expressed in planta is preserved in cell cultures of Nicotiana tabacum inoculated with zoospores of Phytophthora nicotianae

Abstract

We have developed a system that models in vitro the gene-for-gene interaction between intactNicotiana tabacum plants and the Oomycete pathogen Phytophthora nicotianae. Gene-for-gene specificity is preserved in decapitated stems and detached leaf strips inoculated with mycelium, and in intact seedlings, callus and suspension cell cultures inoculated with zoospores of compatible and incompatible races of the pathogen. Zoospores of compatible and incompatible races of the pathogen are attracted to clumps of host cells in suspension cultures, as they are to hypocotyls of intact seedlings. When suspension cells are challenged with zoospores of an incompatible pathogen race the subsequent cellular events that result in hypersensitive cell death are similar in sequence and timing to that observed in hypocotyls. In cells challenged by zoospores of a compatible race of the pathogen, infection and colonization progresses steadily, without any notable host response, until sporangia differentiate 30h after inoculation. Colonized host cells remain viable until this time.