Abstract
Systemic movement of beet necrotic yellow vein virus (BNYVV) in Beta macrocarpa depends on viral RNA3, whereas in Nicotiana benthamiana this RNA is dispensable. RNA3 contains a coremin motif of 20 nucleotides essential for the stabilization of noncoding RNA3 (ncRNA3) and for long-distance movement in Beta species. Coremin mutants that are unable to accumulate ncRNA3 also do not achieve systemic movement in Beta species. A mutant virus carrying a mutation in the p14 viral suppressor of RNA silencing (VSR), unable to move long distances, can be complemented with the ncRNA3 in the lesion phenotype, viral RNA accumulation, and systemic spread. Analyses of the BNYVV VSR mechanism of action led to the identification of the RNA-dependent RNA polymerase 6 (RDR6) pathway as a target of the virus VSR and the assignment of a VSR function to the ncRNA3.
Highlights
In eukaryotic cells, antiviral host defenses counteract virus amplification and cell-to-cell transmission
In Nicotiana benthamiana (N. benthamiana), the p14BA2 mutant of the viral suppressor of RNA silencing (VSR) unable to move long distances [8] is complemented by RNA3, and that noncoding RNA3 (ncRNA3) accumulation plays an essential role in systemic infection, acting as a second VSR
The ncRNA3 Complements the Absence of beet necrotic yellow vein virus (BNYVV) VSR in C. quinoa
Summary
Antiviral host defenses counteract virus amplification and cell-to-cell transmission. The RNA silencing machinery acts against viral amplification and virus systemic movement in plants [1] and is triggered by the occurrence of double-stranded RNA (dsRNA), which can consist of viral replicative intermediates or highly structured RNA. Dicer-like proteins DCL4 or DCL2 process double-stranded RNAs into 21- to 22-nt-long primary small interfering RNAs (siRNAs), respectively. Fungi, and worms, the process of RNA silencing is amplified by RNA-dependent RNA polymerases (RDR). These enzymes synthesize dsRNAs from targeted RNAs and further processing of these dsRNAs by DCL proteins leads to the production of secondary siRNAs [2]. The ability of plants to spread viral siRNAs systemically may play an essential role in antiviral defense
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