Ornithine Carbamoyltransferase Gene Duplication and Phaseolotoxin Resistance in Pseudomonas Syringae Pv. Phaseolicola

Abstract

Several years ago, we raised the question of self-protection against toxins as an important aspect of toxigene-sis by bacterial phytopathogens (Staskawicz et al., 1980; Ponopoulos and Staskawicz, 1982). Since then two bacterial pathogens, Pseudomonas syringae pv. phaseolicola (see below) and Pseudomonas syringae pv. tabaci (Knight et al., 1986; 1987) that produce non host-specific toxins and possess potentially sensitive target enzymes have been examined in this respect. Our studies concern P. syringae pv. phaseolicola, a pathogen on common bean (Phaseolus vulgaris) causing the halo blight disease. Infection on either leaves or pods leads to the formation of watersoaked lesions as a primary symptom of the disease and chlorotic halos, systemic chlorosis and dwarfism as secondary symptoms. A low molecular weight toxin, phaseol otoxin, produced by the bacterium at low growth temperatures (18–20°C) in vitro and in planta is responsible for the secondary symptoms.