A novel fungal effector from Puccinia graminis suppressing RNA silencing and plant defense responses

Summary Fungal plant pathogens, like rust‐causing biotrophic fungi, secrete hundreds of effectors into plant cells to subvert host immunity and promote pathogenicity on their host plants by manipulating specific physiological processes or signal pathways, but the actual function has been demonstrated for very few of these proteins. Here, we show that the Pgt SR 1 effector proteins, encoded by two allelic genes ( Pgt SR 1‐a and Pgt SR 1‐b ), from the wheat stem rust pathogen Puccinia graminis f. sp.  tritici ( Pgt ), suppress RNA silencing in plants and impede plant defenses by altering the abundance of small RNA s that serve as defense regulators. Expression of the Pgt SR 1 s in plants revealed that the Pgt SR 1 s promote susceptibility to multiple pathogens and partially suppress cell death triggered by multiple R proteins. Overall, our study provides the first evidence that the filamentous fungus P. graminis has evolved to produce fungal suppressors of RNA silencing and indicates that Pgt SR 1 s suppress both basal defenses and effector triggered immunity.