Chlorosis-inducing Phytotoxins Produced by Pseudomonas syringae

Pseudomonas syringae causes a wide range of symptoms on plants including blights, leaf spots, and galls. Phytotoxins generally enhance the virulence of phytopathogenic P. syringae, and their synthesis can substantially increase disease severity. Although several P. syringae phytotoxins cause chlorosis (coronatine, phaseolotoxin, and tabtoxin), they are synthesized by unrelated biosynthetic pathways and have completely different modes of action. Phaseolotoxin and tabtoxin inhibit ornithine carbamoyltransferase and glutamine synthetase, respectively, whereas coronatine functions as a mimic of methyl jasmonate in some plant species. This review focusses on the mode of action, genetics, biosynthesis and regulation of coronatine, tabtoxin, and phaseolotoxin. Current techniques used to detect these toxins and phytotoxin-producing P. syringae pathovars are discussed. The utilization of toxin resistance genes in the development of transgenic plants with phytotoxin tolerance is also reviewed.