Pathogens secrete a variety of effectors to compromise host immunity and promote nutrient absorption. The molecular mechanisms by which effectors interfere with plant resistance need to be continuously explored to develop effective strategies for disease prevention and control. In this study, we characterized an effector protein Pst4121 from Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. Pst4121 was significantly upregulated during Pst infection. Transient expression analysis demonstrated that Pst4121 can inhibit basal immune responses in plants. Knocking down Pst4121 led to weakened Pst virulence using host-induced gene silencing. Overexpression and RNA interference (RNAi) of Pst4121 in wheat indicate that Pst4121 is required for Pst infection and pathogenicity. In addition, Pst4121 was found to interact with wheat SNF1-related kinase TaSnRK1α family members and exhibited higher interaction intensity with TaSnRK1.3, the positive regulator of wheat stripe rust resistance. The Pst4121-TaSnRK1.3 interaction resulted in reduced protein kinase activity of TaSnRK1.3. Taken together, our findings reveal that Pst4121 functions as an important virulence factor secreted to impede wheat resistance to stripe rust potentially by attenuating TaSnRK1.3 kinase activity, thereby disrupting the downstream disease resistance regulatory network to help the fungal pathogen achieve successful invasion.
