Characterization and structural analysis of the coat protein from Chinese isolates of Cymbidium mosaic virus

Cymbidium mosaic virus (CymMV) is the most prevalent virus to infect orchids. The coat protein of CymMV (CyCP) is not only necessary for encapsidating the virus RNA and cell-to-cell movement, but also a target to create virus-resistant transgenic orchids. In this report, a CymMV coat protein cDNA (designated as CyCP-CX) was isolated from Chinese isolates of Cymbidium mosaic virus. An extensive search in GenBank database and alignment analysis revealed another 49 CyCP isoforms from the orchids in six different countries. These genes plus CyCP-CX were used for phylogenetic reconstruction, which revealed three groups, namely group I, II and III. The CyCP sequences from the same country were generally not clustered together. Furthermore, the CyCP sequences from the same region or host plant also showed a high divergence. These data indicate that the CymMV has been frequently exchanged among the different countries as a result of the trade of orchids. Structural analysis indicates that the CyCP is similar to the tetratricopeptide repeat (TPR) protein with predicted three tandem TPR repeats. These TPR domains in CyCP structure may have significance in viral disassembly and propagation.