Chlorosis-inducing products from Pseudomonas syringae pathovars: new N-coronafacoyl compounds

Liquid cultures of Pseudomonas syringae pv. tomato strains that also produced the phytotoxin coronatine, were found to have a new chlorosis-inducing activity, not previously described. Bioassay-guided fractionation and HPLC analysis revealed two new peaks that were chlorosis-inducing on leaves of bean plants. Mass spectrometry and NMR analyses of the compounds led to the derivation of their structures as coronafacoyl-L-serine and coronafacoyl-L-threonine, respectively. The amino acid C-2 configurations were determined by GC analysis following hydrolysis with 6M HCl. Both compounds have more polar and more acidic properties than coronatine, norcoronatine, and other known coronafacoyl conjugates with non-polar amino acids. Investigation of Pseudomonas syringae pv. glycinea strains that are known to be prolific producers of the coronatine family of compounds revealed the production of coronafacoylserine and coronafacoylthreonine also.