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- Title
A novel ilarvirus protein CP-RT is expressed via stop codon readthrough and suppresses RDR6-dependent RNA silencing.
- Authors
Lukhovitskaya, Nina; Brown, Katherine; Hua, Lei; Pate, Adrienne E.; Carr, John P.; Firth, Andrew E.
- Abstract
Ilarviruses are a relatively understudied but important group of plant RNA viruses that includes a number of crop pathogens. Their genomes comprise three RNA segments encoding two replicase subunits, movement protein, coat protein (CP), and (in some ilarvirus subgroups) a protein that suppresses RNA silencing. Here we report that, in many ilarviruses, RNA3 encodes an additional protein (termed CP-RT) as a result of ribosomal readthrough of the CP stop codon into a short downstream readthrough (RT) ORF. Using asparagus virus 2 as a model, we find that CP-RT is expressed in planta where it functions as a weak suppressor of RNA silencing. CP-RT expression is essential for persistent systemic infection in leaves and shoot apical meristem. CP-RT function is dependent on a putative zinc-finger motif within RT. Replacing the asparagus virus 2 RT with the RT of an ilarvirus from a different subgroup restored the ability to establish persistent infection. These findings open up a new avenue for research on ilarvirus silencing suppression, persistent meristem invasion and vertical transmission. Author summary: Ilarviruses comprise a group of plant-infecting RNA viruses. Until now, ilarvirus genomes were thought to only encode two components of the viral replicase, a movement protein, the capsid protein, and the 2b suppressor of RNA silencing. Interestingly, whereas most plant viruses encode one or more proteins that suppress the host antiviral RNA silencing pathway, the gene encoding 2b is only present in some ilarviruses. Here, we identify an additional ilarvirus protein that is expressed via low efficiency ribosomal readthrough of the capsid protein (CP) stop codon. Readthrough ribosomes translate a short downstream readthrough (RT) domain to produce the capsid-readthrough fusion protein, CP-RT. We show that CP-RT is a second ilarvirus suppressor of silencing protein and is required for the model ilarvirus asparagus virus 2 to maintain persistent infection in the model plant Nicotiana benthamiana. These findings advance our understanding of ilarvirus molecular virology and virus-host interaction. Interestingly, there are substantial differences in the RT peptide between divergent groups of ilarviruses and, in at least two cases, a separate RT peptide appears to have evolved independently. Thus it will be of future interest to investigate the function of CP-RT in different ilarvirus lineages.
- Subjects
ZINC-finger proteins; PLANT RNA; PLANT viruses; CHIMERIC proteins; PEPTIDES; MOLECULAR virology
- Publication
PLoS Pathogens, 2024, Vol 20, Issue 5, p1
- ISSN
1553-7366
- Publication type
Article
- DOI
10.1371/journal.ppat.1012034