Temperature-Regulated Biosynthesis of Coronatine by Pseudomonas Syringae in vitro and in planta

Abstract

Coronatine (COR) is a chlorosis-inducing phytotoxin produced by the plant pathogenic bacterium Pseudomonas syringae. A variety of environmental factors affect COR production. Previously, it was shown in vitro that temperature had a highly significant effect on COR synthesis in P. s. pv. glycinea PG4180, with maximal production rates at 18°C and low activity at 28°C. However, little was known about the actual expression of biosynthetic genes required for production of COR in planta. Confocal laser scanning microscopy was used to investigate in vitro and in planta expression of COR genes by two model organisms, P. s. pv. glycinea PG4180, a pathogen of soybean, and P. s. pv. tomato DC3000, a pathogen of tomato. The results indicate that the signals for induction of COR biosynthesis differ in these strains. COR biosynthesis by P. s. pv. glycinea PG4180 was temperature-dependent in minimal medium as well as inside the plant tissue. However, transcription of COR biosynthetic genes was not significantly affected by temperature in P. s. pv. tomato DC3000. In contrast, DC3000 showed higher levels of COR gene expression when inoculated into host plants as compared to DC3000 grown in minimal medium.