Trans-replication of, and competition between, DNA beta satellites in plants inoculated with Tomato yellow leaf curl China virus and Tobacco curly shoot virus.

Tomato yellow leaf curl China virus (TYLCCNV) Y10 isolate (Y10) and Tobacco curly shoot virus (TbCSV) Y35 isolate (Y35), both obtained from Yunnan Province, were each found to be associated with a distinct species of satellite DNA (DNA beta). Here, we demonstrate that both Y10 DNA beta (Y10beta) and Y35 DNA beta (Y35beta) were stably trans-replicated by the noncognate Begomovirus, although the noncognate DNA beta accumulated in plants at a lower level than did the cognate DNA beta. In Nicotiana benthamiana and N. glutinosa plants agroinoculated with Y10+Y10beta+Y35beta or with Y35+Y35beta+Y10beta, all components accumulated in the early stages of infection but, at later stages, the noncognate DNA beta decreased in relative concentration and was undetectable at 80 to 120 days after inoculation. The helper viruses and cognate DNA beta species persisted at higher levels throughout the experiments. When the initiation codon of the betaC1 gene of the cognate DNA beta was mutated, the dominance of the cognate over the noncognate DNA beta in mixed infections was unimpaired. These results imply that the cognate DNA beta competes with the noncognate DNA beta and that the ability for selective maintenance of DNA beta is not controlled by the betaC1 protein.