Characterisation of genes involved in biosynthesis of coronafacic acid, the polyketide component of the phytotoxin coronatine

Coronafacic acid (CFA) is the polyketide component of coronatine (COR), a phytotoxin produced by the plant pathogen, Pseudomonas syringae. In the present study we have determined the nucleotide sequence of a 3.92-kb DNA fragment involved in CFA biosynthesis. Analysis of the sequence revealed four complete open reading frames (ORFs) designated cfal to cfa4 and one incomplete ORF (cfa5), all transcribed in the same direction. The predicted translation products of cfal, cfa2 and cfa3 showed relatedness to acyl carrier proteins, fatty acid dehydrases and ß-ketoacylsynthases, respectively, which are required for polyketide synthesis. cfal was subcloned, its sequence was confirmed, and it was overexpressed in E. coli to yield a peptide with an apparent molecular mass of 6 kDa.