Induction of infectious petunia vein clearing (pararetro) virus from endogenous provirus in petunia.

Infection by an endogenous pararetrovirus using forms of both episomal and chromosomal origin has been demonstrated and characterized, together with evidence that petunia vein clearing virus (PVCV) is a constituent of the Petunia hybrida genome. Our findings allow comparative and direct analysis of horizontally and vertically transmitted virus forms and demonstrate their infectivity using biolistic transformation of a provirus-free petunia species. Some integrants within the genome of P.hybrida are arranged in tandem, allowing direct release of virus by transcription. In addition to known inducers of endogenous pararetroviruses, such as genome hybridization, tissue culture and abiotic stresses, we observed activation of PVCV after wounding. Our data also support the hypothesis that the host plant uses DNA methylation to control the endogenous pararetrovirus.