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Virology. 2019 Jul 1;535:111-121. doi: 10.1016/j.virol.2019.06.018. [Epub ahead of print]

Efficient RNA silencing suppression activity of Potato Mop-Top Virus 8K protein is driven by variability and positive selection.

Author information

1
Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Uppsala, Sweden.
2
Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Uppsala, Sweden; Plant Virology Research Centre, College of Agriculture, Shiraz University, Iran.
3
Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Alnarp, Sweden.
4
Department of Plant Breeding, Swedish University of Agricultural Sciences, Alnarp, Sweden.
5
Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow, Russia.
6
Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia; Department of Virology Biological Faculty, Moscow State University, Moscow, Russia.
7
Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Uppsala, Sweden. Electronic address: eugene.savenkov@slu.se.

Abstract

Previously, we investigated the evolution of Potato mop-top virus (PMTV) ORFs. Results indicate that positive selection acts exclusively on an ORF encoding the 8K protein, a weak viral suppressor of RNA silencing (VSR). However, how the extraordinary variability contributes to 8K-mediated RNA silencing suppression remains unknown. Here, we characterized the RNA silencing suppression activity of the 8K protein from seven diverse isolates. We show that 8K encoded by isolate P1 exhibits stronger RNA silencing suppression activity than the 8K protein from six other isolates. Mutational analyses revealed that Ser-50 is critical for these differences. By comparing small RNA profiles we found a lower abundance of siRNAs with U residue at the 5'-terminus after expression of the P1 8K compared to expression of 8K from isolate P125, an isolate with weak VSR activity. These results provide new clues as to the role of positive selection in shaping activities of VSRs.

KEYWORDS:

Natural variation; Next generation sequencing; Plant viruses; RNA silencing; Viral suppressor of RNA silencing; siRNA

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