Analysis of Genes Involved in Biosynthesis of Coronafacic Acid, the Polyketide Component of the Phytotoxin Coronatine

摘要

Coronafacic acid (CFA) is the polyketide component of coronatine (COR), a phytotoxin produced by the plant-pathogenic bacteriumPseudomonas syringae. The genes involved in CFA biosynthesis are encoded by a single transcript which encompasses 19 kb of the COR gene cluster. In the present study, the nucleotide sequence was determined for a 4-kb region located at the 3′ end of the CFA biosynthetic gene cluster. Three open reading frames were identified and designated cfa8, cfa9, andtnp1; the predicted translation products of these genes showed relatedness to oxidoreductases, thioesterases, and transposases, respectively. The translational products of cfa8 andcfa9 were overproduced in Escherichia coliBL21; however, tnp1 was not translated in these experiments. Mutagenesis and complementation analysis indicated thatcfa8 is required for the production of CFA and COR. Analysis of a cfa9 mutant indicated that this gene is dispensable for CFA and COR production but may increase the release of enzyme-bound products from the COR pathway; tnp1, however, had no obvious function in CFA or COR biosynthesis. A genetic strategy was used to produce CFA in a P. syringae strain which lacks the COR gene cluster; this approach will be useful in future studies designed to investigate biosynthetic products of the CFA gene cluster.