Quercetin-induced H2O2 mediates the pathogen resistance against Pseudomonas syringae pv. tomato DC3000 in Arabidopsis thaliana.

Abstract Quercetin is a potent antioxidant and has been extensively used as a therapy intervention to prevent age-associated diseases. However, emerging studies showed it can also act as a prooxidant and induce H 2 O 2 under certain conditions. In the current study, our results showed that quercetin contributed to the pathogen resistance in Arabidopsis thaliana ( Arabidopsis ) in response to the infection of virulent strain Pseudomonas syringae pv. Tomato DC3000 (Pst). Various defense responses, such as H 2 O 2 burst, callose deposition, cell death, PR1 ( pathogenesis-related 1 ) and PAL1 ( Phe ammonia-lyase 1 ) gene expression, have been investigated in quercetin-pretreated Pst-inoculated Arabidopsis Col-0 and there was a strong defensive response in quercetin-pretreated Arabidopsis against virulent Pst. However, with the presence of catalase, the protective effects of quercetin on pathogen resistance to virulent Pst disappeared in Arabidopsis , suggesting that H 2 O 2 may play a key role in plant defense responses. In addition, we confirmed that quercetin did not show any beneficial effect on pathogen-free leaves in Arabidopsis , indicating that pathogen challenge is also required to induce the defense responses in quercetin-pretreated Arabidopsis . Furthermore, strong defense responses have been observed in quercetin-pretreated Arabidopsis mutant jar1 , ein2 , and abi1-2 under Pst challenge, whereas no protective effect has been observed in quercetin-pretreated Arabidopsis mutant NahG and npr1 . These findings indicate that quercetin induces the resistance to Pst in Arabidopsis via H 2 O 2 burst and involvement of SA and NPR1.