Coordinated action of RTBV and RTSV proteins suppress host RNA silencing machinery

Abstract

RNA silencing is as an adaptive immune response in plants that limits accumulation or spread of invading viruses. Successful virus infection entails countering the RNA silencing for efficient replication and systemic spread in the host. The viruses encode proteins having the ability to suppress or block the host silencing mechanism, resulting in severe pathogenic symptoms and diseases. Tungro virus disease caused by a complex of two viruses provides an excellent system to understand these host and virus interactions during infection. It is known that Rice tungro bacilliform virus (RTBV) is the major determinant of the disease while Rice tungro spherical virus (RTSV) accentuates the symptoms. This study brings to focus the important role of RTBV ORF-IV in Tungro disease manifestation, by acting as both the victim and silencer of the RNA silencing pathway. The ORF-IV is a weak suppressor of the S-PTGS or pre-established stable silencing but its suppression activity is augmented in the presence of RTSV proteins. The RTBV and RTSV proteins interact to suppress localized silencing as well as spread of silencing, in the host plants.