Vol. 180, Issue 13, 3330-3338, July 1, 1998
1 Department of Entomology and Plant Pathology,
Oklahoma State University, Stillwater, Oklahoma
74078-3032,1 and
2 Plant Improvement
Division, Horticulture and Food Research Institute of New Zealand,
Auckland, New Zealand2
Coronafacic acid (CFA) is the polyketide component of coronatine
(COR), a phytotoxin produced by the plant-pathogenic bacterium Pseudomonas 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, and
tnp1; the predicted translation products of these genes
showed relatedness to oxidoreductases, thioesterases, and transposases,
respectively. The translational products of cfa8 and
cfa9 were overproduced in Escherichia coli BL21; however, tnp1 was not translated in these
experiments. Mutagenesis and complementation analysis indicated that
cfa8 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.
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