Satellite RNA is essential for encapsidation of groundnut rosette umbravirus RNA by groundnut rosette assistor luteovirus coat protein

Groundnut rosette disease is caused by a complex of agents comprising groundnut rosette umbravirus (GRV), GRV satellite RNA (sat-RNA) and groundnut rosette assistor luteovirus (GRAV). Both GRAV and GRV sat-RNA are needed for GRV to be aphid transmissible. To understand the role of GRAV and GRV sat-RNA in the aphid transmission of GRV, encapsidation of GRV genomic and satellite RNAs has been studied using transgenic Nicotiana benthamiana plants expressing GRAV coat protein (CP). GRAV CP expressed from a transgene was shown to package GRV genomic and satellite RNAs efficiently, giving a high yield of transcapsidated virus particles. GRV sat-RNA was absolutely essential for this process. GRV genomic RNA was not encapsidated by GRAV CP in the absence of the sat-RNA Using different mutants of GRV sat-RNA, it was found that some property of full-length satellite RNA molecules, such as size or specific conformation rather than potential open reading frames, was required for the production of virus particles. A correlation between the ability of sat-RNA to stimulate encapsidation of GRV RNA by GRAV CP and its capacity to promote aphid transmission of GRV was observed. (C) 1999 Academic Press.