GLUCOCORTICOID-INDUCIBLE EXPRESSION OF A BACTERIAL AVIRULENCE GENE INTRANSGENIC ARABIDOPSIS INDUCES HYPERSENSITIVE CELL-DEATH

Pathogenic strains of Pseudomonas syringae pv. tomato carrying the avr Rpt2 avirulence gene specifically induce a hypersensitive cell death r esponse in Arabidopsis plants that contain the complementary RPS2 dise ase resistance gene. Transient expression of avrRpt2 in Arabidopsis pl ants having the RPS2 gene has been shown to induce hypersensitive cell death. In order to analyze the effects of conditional expression of a vrRpt2 in Arabidopsis plants, transgenic lines were constructed that c ontained the avrRpt2 gene under the control of a tightly regulated, gl ucocorticoid-inducible promoter. Dexamethasone-induced expression of a vrRpt2 in transgenic lines having the RPS2 gene resulted in a specific hypersensitive cell death response that resembled a Pseudomonas syrin gae-induced hypersensitive response and also induced the expression of a pathogenesis-related gene (PR1). Interestingly, high level expressi on of avrRpt2 in a mutant rps2-101C background resulted in plant stres s and ultimately cell death, suggesting a possible role for avrRpt2 in Pseudomonas syringae virulence. Transgenic RPS2 and rps2 plants that contain the glucocorticoid-inducible avrRpt2 gene will provide a power ful new tool for the genetic, physiological, biochemical, and molecula r dissection of an avirulence gene-specified cell death response in bo th resistant and susceptible plants.