Involvement of Ralfuranone Production in the Virulence of Ralstonia solanacearum OE1-1

Ralstonia solanacearum causes a destructive disease called bacterial wilt in numerous plant species. Its virulence is controlled by the transcriptional regulator PhcA, the activity of which is, in turn, regulated in a cell-density dependent manner, termed quorum sensing. We herein described the identification and characterization of ralfuranones J-L, new PhcA-regulated secondary metabolites, and the known derivatives, ralfuranones A and B, from R. solanacearum strain OE1-1. Their structures were determined by spectroscopic and chemical methods. These ralfuranones were also detected in vascular exudates from host plants infected with OE1-1. Deletion of ralA, which encodes an enzyme for ralfuranone biosynthesis, reduced the virulence of OE1-1 in tomato plants. Virulence was restored by complementation of the ralA gene. The results suggest that ralfuranones play important roles in the virulence of OE1-1.