The p22 RNA Silencing Suppressor of the Crinivirus Tomato chlorosis virus is Dispensable for Local Viral Replication but Important for Counteracting an Antiviral RDR6-Mediated Response during Systemic Infection

Among the components of the RNA silencing pathway in plants, RNA-dependent RNA polymerases (RDRs) play fundamental roles in antiviral defence. Here, we demonstrate that the Nicotiana benthamiana RDR6 is involved in defence against the bipartite crinivirus (genus Crinivirus, family Closteroviridae) Tomato chlorosis virus (ToCV). Additionally, by producing a p22-deficient ToCV infectious mutant clone (ToCVΔp22), we studied the role of this viral suppressor of RNA silencing in viral infection in both wild-type and RDR6-silenced N. benthamiana (NbRDR6i) plants. We demonstrate that p22 is dispensable for the replication of ToCV, where RDR6 appears not to have any effect. Furthermore, the finding that ToCV∆p22 systemic accumulation was impaired in wild-type N. benthamiana but not in NbRDR6i plants suggests a role for p22 in counteracting an RDR6-mediated antiviral response of the plant during systemic infection.Yazmín Landeo-Ríos was the recipient of a fellowship from the Agencia Española de Cooperación Internacional (AECID). M. Carmen Cañizares was the recipient of an I3P contract from the CSIC (Spain) co-financed by the Fondo Social Europeo (FSE). This work was supported by grants AGL2010-22287-C02-01/AGR and AGL2013-48913-C2-1-R from the Ministerio de Economía y Competitividad, Spain, co-financed by the Fondo Europeo de Desarrollo Regional-FSE. Jesús Navas-Castillo and Enrique Moriones are members of the Research Group AGR-214, which is partially funded by the Consejería de Economía, Innovación y Ciencia, Junta de Andalucía, Spain. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI