HC-Pro hypo- and hypersuppressor mutants: differences in viral siRNA accumulation in vivo and siRNA binding activity in vitro

Viruses have evolved mechanisms to suppress the RNA silencing defense of their hosts, allowing replication and systemic colonization. In a recent study, we found that the effect of mutations in the RNA silencing suppressor of Tobacco etch virus (TEV) was variable, ranging from complete abolition of suppressor activity to significantly stronger suppression. Whereas hyposuppressor mutants were less virulent and accumulated less viral particles than wildtype, hypersuppressors induced symptoms similar to wildtype and accumulated to similar levels. Here we further characterize a set of these mutants in terms of their ability to bind in vitro and induce accumulation in vivo of virus-derived siRNAs. Hyposuppressor alleles are less efficient binding siRNAs than hypersuppressors, whereas the latter are not different from the wildtype. As a consequence of lower viral accumulation, plants infected with virus bearing a hyposuppressor allele also accumulate less virus-derived siRNAs.This work was supported by grants from the Spanish Ministerio de Ciencia e Innovación (MICINN)-Fondo Europeo de Desarrollo Regional (BFU2006-14819-C02-01/BMC), the Generalitat Valenciana (ACOMP07-263) and the European Molecular Biology Organization Young Investigator Program to S.F.E and by grant BIO2008-01986 (MICINN) to J.A.D. C.T.B. was supported by a predoctoral fellowship from the Generalitat Valenciana.Peer reviewe