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

We have developed a system that models in vitro the gene-for-gene interacti on between intact Nicotiana tabacum plants and the Oomycete pathogen Phytop hthora nicotianae. Gene-for-gene specificity is preserved in decapitated st ems and detached leaf strips inoculated with mycelium, and in intact seedli ngs, callus and suspension cell cultures inoculated with zoospores of compa tible and incompatible races of the pathogen. Zoospores of compatible and i ncompatible races of the pathogen are attracted to clumps of host cells in suspension cultures, as they are to hypocotyls of intact seedlings. When su spension cells are challenged with zoospores of an incompatible pathogen ra ce 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 an d colonization progresses steadily, without any notable host response, unti l sporangia differentiate 30 h after inoculation. Colonized host cells rema in viable until this time. (C) 2000 Academic Press.