CaGβ Promotes CaWRKY40 to Activate Immunity Against Ralstonia solanacearum but Disables It from Activating Thermotolerance.

It has previously been found that CaWRKY40 is employed by pepper to activate immunity against Ralstonia solanacearum and to activate thermotolerance context-specifically, but the underlying mechanisms are not fully understood. Here, CaGβ, a subunit in the heterotrimeric G protein complex that was originally found to probably interact with CaWRKY40, was expressional and functionally characterized; the results showed that CaGβ was upregulated by R. solanacearum infection; its silencing by virus-induced silencing impaired pepper immunity against R. solanacearum infection, accompanied by downregulation of immunity-related marker genes, including CaPR1, CaDEF1, CaNPR1, and CaPR-STH2. In addition, CaGβ-CaWRKY40 interaction was confirmed by BiFC and pull-down assay using prokaryotically expressed proteins, and activations of immunity-related CaPR1, CaPR-STH2, and CaNPR1 by CaWRKY40 were all promoted, but the activation of thermotolerance-related CaHSP24 by CaWRKY40 blocked CaGβ through its interaction with CaWRKY40. All these data indicate that immunity against R. solanacearum and its antagonism to thermotolerance in pathogen-infected pepper plants are mediated by CaWRKY40 through physical interaction with CaGβ.