Size reversion of a truncated DNAβ associated with Tobacco curly shoot virus

Our previous results demonstrated that DNAβ associated with Tobacco curly shoot virus (TbCSV) is not necessary for infection but intensifies symptoms in some hosts. To better understand the function of DNAβ in virus infection, a βC1 deleted infectious clone of the TbCSV DNAβ was constructed. Agroinoculation showed that the truncated DNAβ (DNAΔC1β) was trans-replicated by TbCSV in tobacco and Petunia hybrida plants. However, PCR and Southern blot analysis demonstrated that the truncated DNAβ reverted to near wild type component size in some Nicotiana benthamiana, N. glutinosa, N. tabacum Samsun and P. hybrida plants co-inoculated with TbCSV and DNAΔC1β. Sequence analysis of four DNAΔC1β derivatives revealed that the wild type size DNAβ molecules were recombinants between TbCSV DNAβ and the pBinPLUS vector in which dimeric constructs were produced for inoculation. The significance of these findings is discussed with respect to the constraints imposed on begomovirus genome size.