AGO1 and viral infectious disease: There are ten Argonaute (AGO) proteins and several of them have been implicated in antiviral RNA silencing by several lines of evidence: AGO1 [7], AGO2 and AGO5 [8] proteins bind vsiRNAs; AGO1 is up-regulated upon virus infection [7]; ago1 mutants are hyper-susceptible to cucumber mosaic virus (CMV); AGO2 is induced by viral silencing suppressors [9], [10]; and ago1 and ago7 mutant plants are hyper-susceptible to silencing suppressor-minus mutant turnip crinkle virus (TCV) [11].