The Valsa mali Effector VmSR1 Accelerates the Degradation of Tudor-SN2 to Suppress RNA Silencing and Plant Immunity.

The apple Valsa canker caused by Valsa mali is one of the most destructive trunk diseases in apple production and disease management. Understanding the interaction between the pathogen and host is a critical foundation for developing durable disease control technologies. In this study, we showed that VmSR1 from V. mali can suppress the plant immune response and promote pathogen infection. VmSR1 associates with the Tudor staphylococcal nuclease 2 (TSN2) proteins in Malus domestica (apple), Arabidopsis thaliana and Nicotiana benthamiana, promotes degradation of TSN2 proteins, and suppresses the abundance of multiple miRNAs an Silencing of TSN2 significantly reduced the abundance of miRNAs and weakened the resistance of apple leaves to V. mali as well as N. benthamiana to Sclerotinia sclerotiorum. These findings expand the understanding of the function of effectors as RNA silencing suppressors during host-pathogen interactions and deepen the understanding of effectors regulating host immunity.