Suppressors of the Arabidopsis lsd5 cell death mutation identify genes involved in regulating disease resistance responses

Cell death is associated with the development of the plant disease resistan ce hypersensitive reaction (IIR). Arabidopsis hrd mutants that spontaneousl y exhibit cell death reminiscent of the HR were identified previously. To s tudy further the regulatory context in which cell death acts during disease resistance, one of these mutants, lsd5, was used to isolate new mutations that suppress its cell death phenotype. Using a simple lethal screen, nine lsd5 cell death suppressors, designated phx (for the mythological bird Phoe nix that rises from its ashes), were isolated. These mutants were character ized with respect to their response to a bacterial pathogen and oomycete pa rasite. The strongest suppressors-phx2, 3, 6 and 11-1-showed complex, diffe rential patterns of disease resistance modifications. These suppressors att enuated disease resistance to avirulent isolates of the biotrophic Peronosp ora parasitica pathogen, but only phx2 and phx3 altered disease resistance to avirulent strains of Pseudomonas syringae pv tomato. Therefore, some of these phx mutants define common regulators of cell death and disease resist ance. In addition, phx2 and phx3 exhibited enhanced disease susceptibility to different virulent pathogens, confirming probable links between the dise ase resistance and susceptibility pathways.