The phytotoxin COR induces transcriptional reprogramming of photosynthetic, hormonal and defence networks in tomato

Coronatine (COR) is a non-host specific phytotoxin secreted by Pseudomonas syringae pv. tomato that can induce leaf chlorosis and increase the virulence of pathogens during plant–pathogen interactions. Studies have shown that COR can regulate multiple physiological processes in plants, but its involvement in bacterial pathogenesis and plant growth regulation is not well understood. In this study, transcriptome sequencing was carried out on 4-week-old tomato leaves that were either mock-treated or treated with COR. Transcriptome sequencing led to the identification of 6144 differentially expressed genes (DEGs), of which 4361 genes were downregulated and 1783 genes were upregulated upon COR treatment. To obtain functional information on the DEGs, we annotated these genes using GO and KEGG databases. Functional classification analysis showed that the DEGs were primarily involved in photosynthesis, chlorophyll and carotenoid biosynthesis, jasmonic acid (JA) synthesis and phenylpropane metabolism. A total of 23 genes related to chlorophyll biosynthesis had significant changes, of which 22 genes were downregulated and one gene was upregulated, indicating that chlorophyll biosynthesis was inhibited upon COR treatment. A total of 17 photosystem I related genes and 22 photosystem II related genes involving 20 protein subunits were also downregulated. In the JA synthesis pathway, 25 genes were up regulated, and six genes were downregulated in COR treated samples. COR was also involved in the regulation of multiple secondary metabolites. The identified DEGs will help us better understand the virulence effects and physiological functions of COR and provide a theoretical basis for breeding resistance into economically important crops.