Characterization of cymbidium mosaic virus coat protein gene and its expression in transgenic tobacco plants.

Cymbidium mosaic virus (CyMV) is the most prevalent virus infecting orchids. Here, we report the isolation of partial cDNA clones encoding the genomic RNA of CyMV. Like most of the polyadenylated monopartite positive-strand RNA viruses, the open reading frame (ORF) coding for the viral coat protein (CP) is located at the 3' end. The ORF predicts a polypeptide chain of 220 amino acids with a molecular weight of 23,600. Sequence comparison of this ORF to the CP sequences of potato virus X(PVX) and white clover mosaic virus (WClMV) revealed a strong amino acid homology in the mid-portion of the CP, but the overall homology was low. The CyMV CP gene was placed downstream of a cauliflower mosaic virus 35S promoter and the chimaeric gene was transferred into Nicotiana benthamiana. Transgenic plants expressing the CyMV CP were protected against CyMV infection.