A trans-activator-like structure in RCNMV RNA1 evokes the origin of the trans-activator in RNA2

PLoS Pathog. 2020 Jan 6;16(1):e1008271. doi: 10.1371/journal.ppat.1008271. eCollection 2020 Jan.

Abstract

The Red clover necrotic mosaic virus (RCNMV) genome consists of two plus-strand RNA genome segments, RNA1 and RNA2. RNA2 contains a multifunctional RNA structure known as the trans-activator (TA) that (i) promotes subgenomic mRNA transcription from RNA1, (ii) facilitates replication of RNA2, and (iii) mediates particle assembly and copackaging of genome segments. The TA has long been considered a unique RNA element in RCNMV. However, by examining results from RCNMV genome analyses in the ViRAD virus (re-)annotation database, a putative functional RNA element in the polymerase-coding region of RNA1 was identified. Structural and functional analyses revealed that the novel RNA element adopts a TA-like structure (TALS) and, similar to the requirement of the TA for RNA2 replication, the TALS is necessary for the replication of RNA1. Both the TA and TALS possess near-identical asymmetrical internal loops that are critical for efficient replication of their corresponding genome segments, and these structural motifs were found to be functionally interchangeable. Moreover, replacement of the TA in RNA2 with a stabilized form of the TALS directed both RNA2 replication and packaging of both genome segments. Based on their comparable properties and considering evolutionary factors, we propose that the TALS appeared de novo in RNA1 first and, subsequently, the TA arose de novo in RNA2 as a functional mimic of the TALS. This and other related information were used to formulate a plausible evolutionary pathway to describe the genesis of the bi-segmented RCNMV genome. The resulting scenario provides an evolutionary framework to further explore and test possible origins of this segmented RNA plant virus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cucumis sativus
  • Evolution, Molecular
  • Genome, Viral
  • Nucleic Acid Conformation
  • RNA, Viral / chemistry
  • RNA, Viral / physiology*
  • Structure-Activity Relationship
  • Tombusviridae / genetics*
  • Tombusviridae / physiology
  • Trans-Activators / physiology*
  • Virus Assembly

Substances

  • RNA, Viral
  • Trans-Activators

Grants and funding

This research was funded by an NSERC Discovery Grant to KAW. LRN was supported by an NSERC Graduate Scholarship and a Queen Elizabeth II Scholarship in Science and Technology from the Government of Ontario. Funders played no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.