Plant pathogens secrete an arsenal of effector proteins to impair host immunity.Some effectors possess enzymatic activities that can modify their host targets.Previously, we demonstrated that a Phytophthora sojae RXLR effector Avr3b acts as a Nudix hydrolase when expressed in planta;and this enzymatic activity is required for full virulence of P.sojae strain P6497 in soybean(Glycine max).Interestingly, recombinant Avr3b produced by E.coli does not have the hydrolase activity unless it was incubated with plant protein extracts.