Synthetic biology approaches to establish a heterologous production system for coronatines

Coronatine (COR) represents a phytotoxin produced by several pathovars of Pseudomonas syringae. It mediates multiple virulence activities by mimicking the plant stress hormone jasmonoyl-l-isoleucine. Structurally, COR consists of a bicyclic polyketide moiety, coronafacic acid (CFA), which is linked via an amide bond to an unusual ethylcyclopropyl amino acid moiety, coronamic acid (CMA). In our studies, we aimed at establishing and engineering of heterologous COR and CFA production platforms using P. putida KT2440 as host. Based on genetic information of the native producer P. syringae pv. tomato DC3000 a COR biosynthetic gene cluster was designed and reconstituted from synthetic DNA fragments. The applied constructional design facilitated versatile pathway modifications and the generation of various expression constructs, which were evaluated for the production of CFA, COR and its derivatives. By modifications of the gene cluster composition production profiles were directed towards target compounds and valuable information about the function and impact of selected pathway proteins on COR biosynthesis were obtained. Additional engineering of expression vector features, including the use of the constitutive PrpsH promoter and a p15Aori-based transposon backbone, led to the development of an expression strain with promising CFA production yields of > 90 mg/l.