The Cucumber vein yellowing virus Silencing Suppressor P1b Can Functionally Replace HCPro in Plum pox virus Infection in a Host-Specific Manner

摘要

Plant viruses of the genera Potyvirus and Ipomovirus (Potyviridae family) use unrelated RNA silencing suppressors (RSS) to counteract antiviral RNA silencing responses. HCPro is the RSS of Potyvirus spp., and its activity is enhanced by the upstream Pi protein. Distinctively, the ipomovirus Cucumber vein yellowing virus (CVYV) lacks HCPro but contains two PI copies in tandem (P1aP1b), the second of which functions as RSS. Using chimeras based on the potyvirus Plum pox virus (PPV), we found that P1b can functionally replace HCPro in potyviral infections of Nicotiana plants. Interestingly, Pia, the CVYV protein homologous to potyviral PI, disrupted the silencing suppression activity of P1b and reduced the infection efficiency of PPV in Nicotiana benthamiana. Testing the influence of RSS in host specificity, we found that a PI 1)expressing chimera poorly infected PPV's natural host, Prunus persica. Conversely, rib conferred on PPV chimeras the ability to replicate locally in cucumber, CVYV's natural host. The deleterious effect of P1a on PPV infection is host dependent, because the P1aP1b-expressing PPV chimera accumulated in cucumber to higher levels than PPV expressing PM alone. These results demonstrate that a potyvirus can use different RSS, and that particular RSS and upstream Pi-like proteins contribute to defining the virus host range.