Aureusvirus P14 is an efficient RNA silencing suppressor that binds double-stranded RNAs without size specificity

Area of Science:

• Molecular Biology
• Plant Pathology
• Virology
• Gene Regulation

Background:

• RNA silencing is a crucial gene regulatory and antiviral mechanism in eukaryotes, relying on small RNAs for sequence specificity.
• Viruses employ silencing suppressors to counteract plant antiviral defenses, but the evolution and mechanisms of these suppressors are not fully understood.
• Tombusvirus P19 is a known suppressor that binds double-stranded RNAs (dsRNAs) and small interfering RNAs (siRNAs) selectively.

Purpose of the Study:

• To investigate the RNA silencing suppressor of Aureusviruses, closely related to Tombusviruses, to understand the evolution of silencing suppression.
• To characterize the Pothos latent virus (PoLV) P14 protein, a potential silencing suppressor.

Main Methods:

• In vitro binding assays to assess P14's interaction with dsRNAs and siRNAs.
• Analysis of siRNA accumulation in plants infected with PoLV or expressing hairpin transcripts.
• Sequence analysis of P14 and P19 to infer evolutionary relationships.

Main Results:

• PoLV P14 efficiently suppresses both virus-induced and transgene-induced RNA silencing.
• In vitro, P14 binds dsRNAs and siRNAs without apparent size selectivity, unlike P19.
• P14 inhibits silencing by binding dsRNA precursors of siRNAs and potentially by sequestering ds-siRNAs during viral infection.

Conclusions:

• P14 represents a distinct mode of RNA silencing suppression compared to P19, potentially targeting both dsRNA precursors and siRNAs.
• Sequence analysis suggests P14 and P19 evolved from a common ancient dsRNA-binding suppressor.
• This study provides insights into the evolutionary diversification of viral silencing suppressors and their mechanisms.