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

Abstract

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