Molecular Characterization of DNAβ Molecules Associated with Tobacco Leaf Curl Yunnan Virus*

Tobacco leaf curl Yunnan virus (TbLCYNV) isolates Y136 and Y143 were both shown to contain DNAb molecules. Seven DNAb molecules, each consisting of 1334–1341 nucleotides, were cloned and characterized. Sequence comparison showed that they were of two main types: type 1 included five DNAb molecules with 75–99% overall nucleotide sequence identity, and type 2 included two DNAb molecules with >99% overall nucleotide sequence identity. Only 52–54% nucleotide identity was found between the two types of DNAb molecules. The two isolates were associated with both types of DNAb. A relationship dendrogram analysis showed that type 1 DNAb molecules clustered with the DNAb molecules of Tomato yellow leaf curl China virus, whereas type 2 DNAb molecules clustered with the DNAb of Tomato yellow leaf curl Thailand virus. Evidence was also provided that type 2 DNAb molecules may have arisen by recombination between the DNAb of Tobacco curly shoot virus and another unidentified virus. To date, only a single type of DNAb molecule had been found to be associated with one begomovirus. The possible reasons of TbLCYNV associated with two types of DNAb molecules are discussed