Geminiviruses are an important group of circular, single-stranded DNA viruses that cause devastating diseases in crops. Geminiviruses replicate their genomic DNA in the nucleus. The newly-synthesized viral DNA is subsequently transported to the cytoplasm, moved to adjacent cells through plasmodesmata with the help of viral movement proteins, and, ultimately, moved long-distance to establish systemic infection. Thus, the nucleocytoplasmic transportation is crucial for a successful infection by geminiviruses. For Tomato yellow leaf curl virus (TYLCV), the V1 protein is known to bind and shuttle viral genomic DNA, but the role of V2 protein in this process is still unclear. Here, we report that the nucleus-local... More
Geminiviruses are an important group of circular, single-stranded DNA viruses that cause devastating diseases in crops. Geminiviruses replicate their genomic DNA in the nucleus. The newly-synthesized viral DNA is subsequently transported to the cytoplasm, moved to adjacent cells through plasmodesmata with the help of viral movement proteins, and, ultimately, moved long-distance to establish systemic infection. Thus, the nucleocytoplasmic transportation is crucial for a successful infection by geminiviruses. For Tomato yellow leaf curl virus (TYLCV), the V1 protein is known to bind and shuttle viral genomic DNA, but the role of V2 protein in this process is still unclear. Here, we report that the nucleus-localized V1 protein dramatically decreases when co-expressed with V2 protein, and that V2-facilitated nuclear export of V1 protein depends on host exportin-α and a specific V1-V2 interaction. Chemical inhibition of exportin-α or a substitutions at cysteine 85 of V2 protein, which abolishes the V1-V2 interaction, blocks the promoted redistribution of V1 protein to the perinuclear region and the cytoplasm. When the V2C85S mutation is incorporated into a TYLCV infectious clone, the TYLCV-C85S causes delayed onset of very mild symptoms compared to wild-type TYLCV, indicating that the V1-V2 interaction and, thus, V2-mediated nuclear export of V1 protein is crucial for viral spread and systemic infection. Our data point to a critical role of the V2 protein in promoting the nuclear export of the V1 protein, likely by promoting V1-mediated nucleocytoplasmic transportation of TYLCV genomic DNA, and in turn, promoting viral systemic infection.
