Abstract:
Plum pox virus (PPV) is a member of the Potyvirus genus that, in nature, infects trees of the Prunus genus.
Although PPV infects systemically several species of the Nicotiana genus, such as N. clevelandii and N.
benthamiana, and replicates in the inoculated leaves of N. tabacum, it is unable to infect systemically the last
host. The long-distance movement defect of PPV was corrected in transgenic tobacco plants expressing the
5 -terminal region of the genome of tobacco etch virus (TEV), a potyvirus that infects systemically tobacco. The
fact that PPV was unable to move to upper noninoculated leaves in tobacco plants transformed with the same
TEV transgene, but with a mutation in the HC protein (HC-Pro)-coding sequences, identifies the multifunctional
HC-Pro as the complementing factor, and strongly suggests that a defect in an HC-Pro activity is
responsible for the long-distance movement defect of PPV in tobacco. Whereas PPV HC-Pro strongly intensifies
the symptoms caused by potato virus X (PVX) in the PPV systemic hosts N. clevelandii and N. benthamiana, it
has no apparent effect on PVX pathogenicity in tobacco, supporting the hypothesis that long-distance movement
and pathogenicity enhancement are related activities of the potyviral HC proteins. The movement defect
of PPV in tobacco could also be complemented by cucumber mosaic virus in a mixed infection, demonstrating
that at least some components of the long-distance machinery of the potyviruses are not strictly virus specific.
A general conclusion of this work is that the HC-Pro might be a relevant factor for controlling the host range
of the potyviruses
