Impact of Temperature on the Regulation of Coronatine Biosynthesis in Pseudomonas syringae

Abstract

The plant pathogenic bacterium Pseudomonas syringae pv. glycinea PG4180 synthesizes high levels of the phytotoxin coronatine (COR) at the virulence- promoting temperature of 18°C, but only low amounts at 28°C, the optimal growth temperature. The temperature-dependent COR gene expression is regulated by a modified two-component system, consisting of the histidine protein kinase CorS, a response regulator, CorR, and a third functionally essential protein, CorP. We ana- lyzed at the transcriptional and translational level the expression of corS and the cma operon involved in COR biosynthesis, after a temperature downshift from 28°C to 18°C. The synthesis of cma mRNA was induced within 20 min and then increased steadily and gradually in the 14 h following the shift to 18°C. The synthe- sis of corS mRNA was induced to a lesser extent by the temperature downshift. The induction of cma expression was a result of accelerated transcription rather than increased stability of the cma transcript at 18°C. Accumulation of the COR bio- synthetic protein CmaB correlated with accumulation of cma mRNA. However, cma transcription was suppressed by inhibition of de novo protein biosynthesis.