It is possible to name "collaborative" plant action for virus such as an activation of pararetroviruses in plant tissue. There is no examples of positive effect of virus on plant tissue so far.
Iskra-Caruana, Marie-Line, et al. "A four-partner plant–virus interaction: enemies can also come from within." Molecular plant-microbe interactions 23.11 (2010): 1394-1402.
I am not sure at all that "collaborative" relationship plant-virus exist, but our results proved that the effect of viruses was followed by plant recovery after transgenesis (see reference)