Pseudomonas syringae Catalases Are Collectively Required for Plant Pathogenesis

Abstract

ABSTRACTThe bacterial pathogenPseudomonas syringaepv. tomato DC3000 must detoxify plant-produced hydrogen peroxide (H2O2) in order to survive in its host plant. Candidate enzymes for this detoxification include the monofunctional catalases KatB and KatE and the bifunctional catalase-peroxidase KatG of DC3000. This study shows that KatG is the major housekeeping catalase of DC3000 and provides protection against menadione-generated endogenous H2O2. In contrast, KatB rapidly and substantially accumulates in response to exogenous H2O2. Furthermore, KatB and KatG have nonredundant roles in detoxifying exogenous H2O2and are required for full virulence of DC3000 inArabidopsis thaliana. Therefore, the nonredundant ability of KatB and KatG to detoxify plant-produced H2O2is essential for the bacteria to survive in plants. Indeed, a DC3000 catalase triple mutant is severely compromised in its ability to growin planta, and its growth can be partially rescued by the expression ofkatB,katE, orkatG. Interestingly, our data demonstrate that although KatB and KatG are the major catalases involved in the virulence of DC3000, KatE can also provide some protectionin planta. Thus, our results indicate that these catalases are virulence factors for DC3000 and are collectively required for pathogenesis.