Pelarspovirus

VIRION

Non-enveloped, spherical, icosahedral, about 28-34 nm in diameter, capsid with a T=3 icosahedral symmetry. 30 hexameric capsomers per nucleocapsid (virion composed of 180 protein subunits).

GENOME

Monopartite, linear, ssRNA(+) genome of 3.9 kb.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. Five ORFs are encoded: p27, its readthrough product p87 which encodes the RdRp, two small movement proteins MP1 and MP2, and the capsid protein (CP) which also acts as suppressor of RNA silencing. A single tricistronic subgenomic RNA is produced for expression of MP and CP genes. M2 movement protein initiates at a non-AUG start codon.

REPLICATION

CYTOPLASMIC

  1. Virus penetrates into the host cell.
  2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
  3. The viral RNA is translated to produce the two proteins necessary for RNA synthesis (replication and transcription).
  4. Replication takes place in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
  5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
  6. The RdRp recognizes internal subgenomic promoters on the negative-sense RNA to transcribe the 3’co-terminal subgenomic RNAs that will generate the capsid and movement protein.
  7. Virus assembly in the cytoplasm.
  8. Viral movement protein probably mediates virion cell-to-cell transfer.