Recovery of virus-infected Dendrobium orchids by constitutive expression of the cymbidium mosaic virus coat protein gene

Abstract

A common practice in the production of viral disease-resistant plant varieties is the transfer of the viral coat protein (CP) gene to a wide range of healthy plants. This is the first report on the effect of a bombarded CP transgene on the replication of cymbidium mosaic virus (CymMV) in naturally infected Dendrobium orchids. Nine months after transformation, two naturally CymMV-infected transgenic Dendrobium orchids exhibited a gradual decrease in CymMV-CP transcript and coat protein levels as detected by RT-PCR and western blot hybridization, respectively. At 18 months, the transgenic lines were completely free of endogenous CymMV contamination and were protected from CymMV re-infection following inoculation. Six weeks after inoculation with purified CymMV, these virus-free transgenic lines contained no viral coat protein transcript, replicase transcript or particle accumulation from the re-invading CymMV, as detected by RT-PCR and Immunoelectron microscopy assays, respectively. Additionally, no small RNAs derived from viral CymMV-CP were detected, but the transcribed CymMV-CP positive-strand derived from the transgene appeared in these transgenic lines.