Profiling small RNAs in soybean Williams 82 (rsv)， susceptible to Soybean mosaic virus (SMV， the genus Potyvirus， family Potyviridae) strains G2 and G7， and soybean PI96983 (Rsv1)， resistant to G2 but susceptible to G7， identified the microRNA miR168 that was highly overexpressed only in G7-infected PI96983 showing a lethal systemic hypersensitive response (LSHR). Overexpression of miR168 was in parallel with the high-level expression of AGO1 mRNA， high-level accumulation of miR168-mediated AGO1 mRNA cleavage products but with severely repressed AGO1 protein. In contrast， AGO1 mRNA， degradation products and protein remained without significant changes in G2- and G7-infected Williams 82. Moreover， knock-down of SGS3， an essential component in RNA silencing， suppressed AGO1 siRNA， partially recovered repressed AGO1 protein， and alleviated LSHR severity in G7-infected Rsv1 soybean. These results suggest that both miRNA and siRNA pathways are involved in G7 infection of Rsv1 soybean， and LSHR is associated with breakdown of AGO1 homeostasis.