Presence of poly(A) and poly(A)-rich tails in a positive-strand RNA virus known to lack 3׳ poly(A) tails

•Tobacco mosaic virus does possess a small fraction of gRNA bearing the polyadenylate tails.•The polyadenylated RNA species are not enriched in chloroplasts.•The chloroplast PNPase is absent of the viral RNA polyadenylation.•Similar types of polyadenylate tail widely present in positive-strand RNA viruses known to lack 3׳ poly(A) tails.

Here we show that Tobacco mosaic virus (TMV), a positive-strand RNA virus known to end with 3׳ tRNA-like structures, does possess a small fraction of gRNA bearing polyadenylate tails. Particularly, many tails are at sites corresponding to the 3׳ end of near full length gRNA, and are composed of poly(A)-rich sequences containing the other nucleotides in addition to adenosine, resembling the degradation-stimulating poly(A) tails observed in all biological kingdoms. Further investigations demonstrate that these polyadenylated RNA species are not enriched in chloroplasts. Silencing of cpPNPase, a chloroplast-localized polynucleotide polymerase known to not only polymerize the poly(A)-rich tails but act as a 3׳ to 5׳ exoribonuclease, does not change the profile of polyadenylate tails associated with TMV RNA. Nevertheless, because similar tails were also detected in other phylogenetically distinct positive-strand RNA viruses lacking poly(A) tails, such kind of polyadenylation may reflect a common but as-yet-unknown interface between hosts and viruses.