RadB6 Influences Multiple Virulence in Dickeya oryzae EC1 through the TzpS/TzpA Two-Component System

Abstract Dickeya species are the major plant pathogens causing bacterial soft rot in numerous crops and ornamentals, resulting in significant economic losses. Previous studies demonstrated that the TzpS/TzpA two-component system (TCS) modulates pathogenicity mainly by regulating the production of phytotoxin zeamines in Dickeya oryzae EC1. However, the virulence regulatory mechanisms associated with this TCS have not been elucidated. In this study, the gene radB6 related to TzpS/TzpA TCS was identified through transposon mutagenesis screening. Overexpression of radB6 in EC1 reduced zeamine production by 80% and markedly downregulated the levels of tzpS, tzpA, and zeamine biosynthesis genes. Furthermore, in strain EC1, various quorum-sensing systems participate in the regulation of virulence factors. Point mutations at Ser116, Thr117, and Pro118 in RadB6 significantly impaired its activity. In summary, these findings provide new insights into the associated regulatory networks of TzpS/TzpA and their roles in modulating pathogenicity.