|Kun Zhang,Yongliang Zhang,Dawei Li etal.The Barley stripe mosaic virusγb protein promotes chloroplast-targeted replication by enhancing unwinding of RNA duplexes.PLOS Pathogens. DOI:10.1371/journal.ppat.1006319|
Kun Zhang, Yongliang Zhang, Meng Yang, Songyu Liu, Zhenggang Li, Xianbing Wang, Chenggui Han, Jialin Yu, Dawei Li
RNA viruses encode various RNA binding proteins that function in many steps of viral infection cycles. These proteins function as RNA helicases, methyltransferases, RNA-dependent RNA polymerases, RNA silencing suppressors, RNA chaperones, movement proteins, and so on. Although many of the proteins bind the viral RNA genome during different stages of infection, our knowledge about the coordination of their functions is limited. In this study, we describe a novel role for the Barley stripe mosaic virus (BSMV)γb as an enhancer ofαa RNA helicase activity, and we show that theγb protein is recruited by theαa viral replication protein to chloroplast membrane sites of BSMV replication. Mutagenesis or deletion ofγb from BSMV resulted in reduced positive strand (+) RNAα accumulation, but γb mutations abolishing viral suppressor of RNA silencing (VSR) activity did not completely eliminate genomic RNA replication. In addition, cis- or trans-expression of the Tomato bushy stunt virus p19 VSR protein failed to complement the γb replication functions, indicating that the direct involvement of γb in BSMV RNA replication is independent of VSR functions. These data support a model whereby two BSMV-encoded RNA-binding proteins act coordinately to regulate viral genome replication and provide new insights into strategies whereby double-stranded viral RNA unwinding is regulated, as well as formation of viral replication complexes.