Construction of watermelon mosaic virus-Beijing isolate infectious clone and study of the dynamic localization and accumulation of virus-encoded proteins.

Potyvirus is the largest genus of plant RNA viruses, and the members in the genus are known to cause significant damage to a wide variety of crops. In this study, we performed small RNA (sRNA) deep sequencing for identification of potential virus (es) in collected cucumber leaves with mosaic symptoms from fields in Beijing. Through this high-throughput sequencing and subsequent PCR amplification, we obtained a complete viral genome sequence of 10,044 bp, which showed the highest similarity to the watermelon mosaic virus (WMV) isolate FBR04-37 and exhibited the typical characteristics of potyviruses in its genome organization. The obtained WMV isolate was designated as WMV-BJ. We then constructed the infectious clone of WMV-BJ, which can successfully infect six kinds of cucurbitaceous plants by agroinfiltration. Among these, Cucumis melo showed obvious symptoms such as shrinkage and mosaic compared to other cucurbitaceous plants infected by this virus infectious clone. To understand the biological function of WMV-BJ, we further analyzed the dynamic subcellular localization and protein accumulation of WMV-BJ encoded 11 viral proteins. The results showed the WMV-BJ-encoded proteins displayed diverse subcellular localizations, and most viral proteins were easily degraded after expression in plant cells. Together, the construction of the WMV-BJ infectious clone in this study provides a valuable tool for further exploring the biology of this virus and the interaction between WMV-BJ and host plant, and useful information for investigating the functions of WMV-encoded proteins.