Cloning and Characterization of Genes Encoding Phaseolotoxin, the Toxin Produced by Pseudomonas Syringae Pv. Phaseolicola

Abstract

Pseudomonas svri ngae pv. phaseolicola is the causal agent of halo blight of bean (Phaseolus vulgaris L.). It produces an extracellular, nonspecific, chlorosis-inducing toxin, phase-olotoxin (Figure 1, Moore et al., 1984). It was previously reported that phaseolotoxin is a potent inhibitor of the ornithine cycle enzyme, ornithine carbamoyl transferase (OCT) of bean in vitro (Patil et al., 1970; Kwok et al., 1979), and that a peptidase degradation product of phaseolotoxin which also inhibits OCT is responsible for symptom production in infected bean plants (Mitchell and Bieleski, 1977). The degradation product, octicidin (Moore et al., 1984), which lacks the alanyl-homoarginine dipeptide moiety is 20 times more active against bean OCT than is phaseolotoxin (Kwok and Patil, 1982). Octicidin-induced chlorosis and growth inhibition in bean tissues can be reversed by L-citrulline and L-arginine. Phaseolotoxin also inhibits the OCT of Escherichia coli k -12 which leads to growth inhibition. This can also be reversed by L-citrulline and L-arginine, a finding used to develop a phaseolotoxin-specific microbial assay (Staskawicz and Panopoulos, 1979).