Phytophthora Pathogens Manipulate Plant Small RNAs to Promote Infection

A broad range of parasites rely on the functions of effector proteins to subvert host immune response and facilitate disease development. The notorious Phytophthora pathogens evolved effectors with RNA silencing suppression activity to promote infection in plant hosts. Small RNAs have been shown to regulate immunity, which requires transcriptional reprogramming. The Phytophthora effector PSR2 specifically affects the accumulation of phased small interfering RNAs (phasiRNAs), which are secondary siRNAs derived from coding or noncoding loci using miRNAs as the triggers. Arabidopsis thaliana mutants defective in phasiRNA production are compromised in defense against Phytophthora infection, indicating that the phasiRNA pathway plays a positive role in plant immunity. Here, we report the identification of specific phasiRNAs that regulate immune response and discuss the molecular mechanism by which PSR2 suppresses phasiRNA biogenesis and promotes infection.