Background: The bacterial type III secretion system (T3SS) is one of the virulence determinants of Gram-negative bacteria through which various effector and virulence proteins are translocated into host cells.
Results: We constructed an assay system to screen inhibitors of hrpA gene expression (a structural gene of Hrp pili) in Pseudomonas syringae pv. tomato DC3000. In a plant extract library screening, the root extract of Vitis vinifera L. displayed the most prominent activity. Three resveratrol oligomers, hopeaphenol, isohopeaphenol and ampelopsin A, were identified in grapevine root extract, which significantly reduced the transcription levels of the hrpA, hrpL and hopP1 genes without growth retardation. Additional resveratrol derivatives identified in other plant extracts were also examined for their inhibitory effect on hrpA expression. Another resveratrol oligomer, kobophenol A, also inhibited the transcription of the hrpA gene and other T3SS-related genes, while resveratrol monomers (resveratrol and piceatannol) were not effective. The severity of bacterial specks was reduced by each hopeaphenol, isohopeaphenol and ampelopsin A treatment.
Conclusion: These results show the potential of resveratrol derivatives as anti-virulence agents for the control of plant diseases.
Keywords: Pseudomonas syringae pv. tomato; bacterial speck; resveratrol oligomer; type III secretion system inhibitor.
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