Quorum Sensing Molecule C-HSL Induces Systemic Resistance to TMV Infection via Upregulation of / Expressions in .

G-negative bacteria produce myriad -acyl-homoserine lactones (AHLs) that can function as quorum sensing (QS) signaling molecules. AHLs are also known to regulate various plant biological activities. -Coumaroyl-homoserine lactone (C-HSL) is the only QS molecule produced by a photosynthetic bacterium, . The role of C-HSL in the interaction between and plant has not been investigated. In this study, we investigated the effect of C-HSL on plant immunity and found that this QS molecule can induce a systemic resistance to (TMV) infection in . The results show that C-HSL treatment can prolong the activation of two mitogen-associated protein kinase genes (i.e., and ) and increase the expression of transcription factor as well as immune response marker genes and , leading to an increased accumulation of reactive oxygen species (ROS) in the TMV-infected plants. Our results also show that C-HSL treatment can increase activities of two ROS-scavenging enzymes, peroxidase and superoxide dismutase. Knockdown of or expression in plants through virus-induced gene silencing nullified or attenuated C-HSL-induced systemic resistance, indicating that the functioning of C-HSL relies on the activity of those two kinases. Meanwhile, C-HSL-pretreated plants also showed a strong induction of kinase activities of NbSIPK and NbWIPK after TMV inoculation. Taken together, our results demonstrate that C-HSL treatment increases plant resistance to TMV infection, which is helpful to uncover the outcome of interaction between and its host plants.