Abstract
P0 proteins encoded by poleroviruses Brassica yellows virus (BrYV) and Potato leafroll virus (PLRV) are viral suppressors of RNA silencing (VSR) involved in abolishing host RNA silencing to assist viral infection. However, other roles that P0 proteins play in virus infection remain unclear. Here, we found that C-terminal truncation of P0 resulted in compromised systemic infection of BrYV and PLRV. C-terminal truncation affected systemic but not local VSR activities of P0 proteins, but neither transient nor ectopic stably expressed VSR proteins could rescue the systemic infection of BrYV and PLRV mutants. Moreover, BrYV mutant failed to establish systemic infection in DCL2/4 RNAi or RDR6 RNAi plants, indicating that systemic infection might be independent of the VSR activity of P0. Partially rescued infection of BrYV mutant by the co-infected PLRV implied the functional conservation of P0 proteins within genus. However, although C-terminal truncation mutant of BrYV P0 showed weaker interaction with its movement protein (MP) when compared to wild-type P0, wild-type and mutant PLRV P0 showed similar interaction with its MP. In sum, our findings revealed the role of P0 in virus systemic infection and the requirement of P0 carboxyl terminal region for the infection.
Highlights
RNA silencing is a natural host antiviral defense pathway at the nucleic acid level [1,2].It occurs through the processing of double-stranded RNAs into complementary short (21–24 nucleotides) interfering RNAs by the Dicer-like enzyme RNAse III [3,4].These siRNAs are loaded into RNA-induced silencing complexes to degrade viral RNAs [5,6].Resulting fragments are converted into dsRNAs with the help of RNA-dependent RNA polymerases (RDRs) and the cofactor suppressor of gene silencing 3 (SGS3), which is encoded by the plant host, to yield secondary siRNAs [7,8]
We revealed that deletion of 25 amino acids in the C-terminus of Brassica yellows virus (BrYV) P0 abolished its systemic RNA silencing suppression activity without affecting the local RNA
We deleted 15 amino acids in the C-terminus of P0Br (P0Br∆235–249 ) (Figure 1a) and evaluated suppressor activity of this mutant by Agrobacterium-mediated transient co-expression assay with pGDG in N. benthamiana leaves
Summary
RNA silencing is a natural host antiviral defense pathway at the nucleic acid level [1,2].It occurs through the processing of double-stranded RNAs into complementary short (21–24 nucleotides) interfering RNAs (siRNAs) by the Dicer-like enzyme RNAse III [3,4].These siRNAs are loaded into RNA-induced silencing complexes to degrade viral RNAs [5,6].Resulting fragments are converted into dsRNAs with the help of RNA-dependent RNA polymerases (RDRs) and the cofactor suppressor of gene silencing 3 (SGS3), which is encoded by the plant host, to yield secondary siRNAs [7,8]. RNA silencing is a natural host antiviral defense pathway at the nucleic acid level [1,2]. It occurs through the processing of double-stranded RNAs into complementary short (21–24 nucleotides) interfering RNAs (siRNAs) by the Dicer-like enzyme RNAse III [3,4]. In spite of the considerable sequence differences, P0 proteins from different poleroviruses still share several motifs or region, which are essential for suppression of RNA silencing. These include the F-box-like motif, G139/W140/G141-like motif and the C-terminal conserved region. Recent studies demonstrated that polerovirus-encoded P0 proteins can target the membrane-bound
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