Sequence divergence in new strains of Tomato leaf curl virus resulting in replication specificity

The complete nucleotide sequences of two new strains (D1 and D2) of Tomato leaf curl virus (TLCV) from Darwin, Australia, were determined. The D1 and D2 strains had an overall nucleotide sequence identity of ca. 95% with the type strain, but within the origin of DNA replication (ori), their sequence identity was only ca. 80%. Agroinfection of dimeric DNA clones of the D1 and type strains revealed that both viruses replicate simultaneously in the same host plant, resulting in the accumulation of respective viral DNA. The ability of the D1 strain to complement a type strain mutant, defective in the replication associated protein gene C1, was examined. The D1 strain failed to complement the type strain mutant. In contrast, complementation of the C1 mutant was achieved with a type strain construct containing a mutation in the C2 ORF. These results suggest that TLCV divergence may arise from small changes in the viral origin of DNA replication.