Beet necrotic yellow vein virus (BNYVV) is a devastating pathogen for sugar beet crops. A study conducted by researchers from the Institute of Molecular Plant Biology (IBMP, CNRS, University of Strasbourg), with support from the Strasbourg Esplanade Proteomics Platform (IBMC/IBMP, CNRS, University of Strasbourg), reveals an unprecedented molecular mechanism involving a viral non-coding RNA, ncRNA3, and the viral silencing suppressor protein p14. Published in the journal Viruses, this work demonstrates how ncRNA3 accumulates in the nucleus of plant cells to disrupt the interaction between p14 and DRB4, a key protein in the plant’s antiviral defense pathway.
BNYVV is a multipartite virus whose systemic spread depends on the accumulation of ncRNA3, a non-coding RNA derived from the cleavage of genomic RNA3. The researchers demonstrated that, unlike the viral genomic RNAs, which remain in the cytoplasm, ncRNA3 is specifically targeted to the nucleus. Once in the nucleus, ncRNA3 disrupts the interaction between p14, a viral silencing suppressor, and DRB4, a cofactor of DCL4, an enzyme essential for the production of small interfering RNAs (siRNAs). This interaction, stabilized in a hypomorphic mutant of p14 (p14BA2), is destabilized in the presence of ncRNA3, thereby allowing the virus to bypass the plant’s defense mechanisms.
To reach these conclusions, the researchers used a combination of innovative approaches, including immunoprecipitation, TurboID proximity labeling coupled with mass spectrometry, as well as confocal microscopyand FRET-FLIM analyses to study protein interactions in vivo. They also performed subcellular fractionation to precisely localize viral RNAs and confirm that ncRNA3 accumulates in the nucleus, where it plays a key role in suppressing RNA silencing.
These findings highlight a fine-tuning mechanism in which ncRNA3 acts as an allosteric modulator, converting a hypomorphic version of p14 into a functional form while disrupting the transitivity pathway of siRNAs. This work opens up perspectives for understanding how viruses manipulate plant defense pathways and could inspire new antiviral strategies.
