Kaempferol promotes bacterial pathogen resistance through the activation of NPR1 by both SA and MPK signaling pathways in Arabidopsis

Flavonoids have a variety of biological functions including UV protectant, antioxidant, allelopathy and auxin transport inhibitor in plants. In addition, flavonoids are implicated in defense response against pathogens. In this study, we found that kaempferol, a kind of flavonol, induces bacterial pathogen resistance. In addition, we identified the signaling pathway to explain how kaempferol can induce pathogen resistance in Arabidopsis. We showed that kaempferol upregulates the tran-scription of two pathogenesis-related (PR) genes. Interestingly, the monomerization and nuclear translocation of NPR1, a key regulator of PR gene expression, was induced by kaempferol through the accumulation of salicylic acid (SA). Further-more, we found that the kaempferol-induced monomerization of NPR1 is mediated by the activation of MPK3 and MPK6. Taken together, this study suggests that kaempferol induces pathogen resistance by both SA and MPK-dependent signaling pathways in Arabidopsis.