Mungbean yellow mosaic Indian virus encoded AC2 protein suppresses RNA silencing by inhibiting Arabidopsis RDR6 and AGO1 activities

- MYMIV-AC2 interferes with the biogenesis of siRNA by interacting and blocking the RDR6 activity.
- MYMIV-AC2 abrogates the tasi-RNA biogenesis in-planta in transient assay.
- MYMIV-AC2 interacts with AGO1 and inhibits its transcript slicing activity in vitro.

RNA silencing refers to a conserved RNA-directed gene regulatory mechanism in a wide range of eukaryotes. It plays an important role in many processes including growth, development, genome stability, and antiviral defense in the plants. Geminivirus encoded AC2 is identified as an RNA silencing suppressor protein, however, the mechanism of action has not been characterized. In this paper, we elucidate another mechanism of AC2-mediated suppression activity of Mungbean Yellow Mosaic India Virus (MYMIV). The AC2 protein, unlike many other suppressors, does not bind to siRNA or dsRNA species and its suppression activity is mediated through interaction with key components of the RNA silencing pathway, viz., RDR6 and AGO1. AC2 interaction inhibits the RDR6 activity, an essential component of siRNA and tasi-RNA biogenesis and AGO1, the major slicing factor of RISC. Thus the study identifies dual sites of MYMIV-AC2 interference and probably accounts for its strong RNA silencing suppression activity.