title: Oleanolic Acid Induces the Type III Secretion System of Ralstonia solanacearum.
abstract: Ralstonia solanacearum, the causal agent of bacterial wilt, can naturally infect a wide range of host plants. The type III secretion system (T3SS) is a major virulence determinant in this bacterium. Studies have shown that plant-derived compounds are able to inhibit or induce the T3SS in some plant pathogenic bacteria, though no specific T3SS inhibitor or inducer has yet been identified in R. solanacearum. In this study, a total of 50 different compounds were screened and almost half of them (22 of 50) significantly inhibited or induced the T3SS expression of R. solanacearum. Based on the strong induction activity on T3SS, the T3SS inducer oleanolic acid (OA) was chosen for further study. We found that OA induced the expression of T3SS through the HrpG-HrpB pathway. Some type III effector genes were induced in T3SS inducing medium supplemented with OA. In addition, OA targeted only the T3SS and did not affect other virulence determinants. Finally, we observed that induction of T3SS by OA accelerated disease progress on tobacco. Overall our results suggest that plant-derived compounds are an abundant source of R. solanacearum T3SS regulators, which could prove useful as tools to interrogate the regulation of this key virulence pathway.
authors.affiliation: Laboratory of Natural Products Pesticides, College of Plant Protection, Southwest University Chongqing, China.
authors.forename: Dousheng
authors.initials: D
authors.lastname: Wu
authors.affiliation: Laboratory of Natural Products Pesticides, College of Plant Protection, Southwest University Chongqing, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.affiliation: Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University Chongqing, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Laboratory of Natural Products Pesticides, College of Plant Protection, Southwest University Chongqing, China.
authors.forename: Xuejiao
authors.initials: X
authors.lastname: Liu
authors.affiliation: Laboratory of Natural Products Pesticides, College of Plant Protection, Southwest University Chongqing, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Yang
keywords: R. solanacearum; induction; oleanolic acid; plant-derived compounds; type III secretion system