THE PLANT CELL, Vol 5, Issue 11 1669-1679, Copyright © 1993 by American Society of Plant Biologists
Expansion of Viral Host Range through Complementation and Recombination in Transgenic Plants
J. E. Schoelz and W. M. Wintermantel
Department of Plant Pathology, University of Missouri, Columbia, Missouri, 65211
We have shown previously that gene VI of cauliflower mosaic virus (CaMV)
strain D4 governs systemic infection of Nicotiana bigelovii and that
transgenic N. bigelovii expressing the D4 gene VI product can complement at
least one CaMV isolate for long-distance transport. We have now found that
DNA of two other isolates of CaMV recombine with the gene VI coding
sequence present in the transgenic plants. The formation of recombinant
viruses occurs as a consequence of CaMV replication, involving two template
switches during reverse transcription of the CaMV RNA to DNA. The first
template switch occurs at the 5[prime] end of the 35S RNA to the gene VI
mRNA produced by the transgenic plants. A second switch occurs at the
5[prime] end of the gene VI mRNA back to the 35S RNA. We also demonstrate
that CaMV can acquire sequences from transgenic plants that alter the
symptomatology and host range of the virus, an observation that may have
important risk assessment implications for strategies using
pathogen-derived resistance to protect plants against virus diseases.
