Formation of Potato Virus A-Induced RNA Granules and Viral Translation Are Interrelated Processes Required for Optimal Virus Accumulation

PLoS Pathog. 2015 Dec 7;11(12):e1005314. doi: 10.1371/journal.ppat.1005314. eCollection 2015 Dec.

Abstract

RNA granules are cellular structures, which play an important role in mRNA translation, storage, and degradation. Animal (+)RNA viruses often co-opt RNA granule proteins for viral reproduction. However, the role of RNA granules in plant viral infections is poorly understood. Here we use Potato virus A (PVA) as a model potyvirus and demonstrate that the helper component-proteinase (HCpro), the potyviral suppressor of RNA silencing, induces the formation of RNA granules. We used confocal microscopy to demonstrate the presence of host RNA binding proteins including acidic ribosomal protein P0, argonaute 1 (AGO1), oligouridylate-binding protein 1 (UBP1), varicose (VCS) and eukaryotic initiation factor iso4E (eIF(iso)4E) in these potyvirus-induced RNA granules. We show that the number of potyviral RNA granules is down-regulated by the genome-linked viral protein (VPg). We demonstrated previously that VPg is a virus-specific translational regulator that co-operates with potyviral RNA granule components P0 and eIF(iso)4E in PVA translation. In this study we show that HCpro and varicose, components of potyviral RNA granules, stimulate VPg-promoted translation of the PVA, whereas UBP1 inhibits this process. Hence, we propose that PVA translation operates via a pathway that is interrelated with potyviral RNA granules in PVA infection. The importance of these granules is evident from the strong reduction in viral RNA and coat protein amounts that follows knock down of potyviral RNA granule components. HCpro suppresses antiviral RNA silencing during infection, and our results allow us to propose that this is also the functional context of the potyviral RNA granules we describe in this study.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytoplasmic Granules / genetics
  • Cytoplasmic Granules / metabolism
  • Gene Knockdown Techniques
  • Host-Parasite Interactions / physiology*
  • Microscopy, Confocal
  • Nicotiana
  • Plant Diseases / genetics*
  • Potyviridae / genetics
  • Potyviridae / metabolism
  • Potyviridae / pathogenicity*
  • Protein Biosynthesis / genetics
  • RNA, Viral / genetics*
  • Viral Proteins / genetics
  • Viral Proteins / metabolism

Substances

  • RNA, Viral
  • Viral Proteins

Grants and funding

This study was supported by a grant from the Academy of Finland (grant number 1138329; http://www.aka.fi) to KM. AL is a fellow of the Integrative Life Science Doctoral Program (http://www.finbionet.fi/ils). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.