VIRION
Non-enveloped, flexuous, filamentous, of one (690-720nm) or two (500-600 and 200-300 nm) lengths x 11-15 nm in diameter. Symmetry helical. Presence of characteristic inclusion bodies within infected plant cells.
GENOME
Monopartite, linear, ssRNA(+) genome of 9-10 kb in size. 3' terminus has a poly (A) tract. 5' terminus has a genome-linked protein (VPg).
GENE EXPRESSION
The virion RNA is infectious and serves as both the genome and viral messenger RNA. The genomic RNA (or genome segments) is translated into polyprotein(s) which is subsequently processed by virus-encoded proteases into functional products. P3N-PIPO is expressed by polymerase slippage mechanism from the P3 ORF and probably acts as a movement protein.
Cleavage sites in the family Potyviridae
ENZYMES
- RNA-dependent RNA polymerase [Nlb-RdRp]
- VPG-type capping [VPg]
- Self cleavage N-ter polyprotein (Peptidase S30) [P1-pro]
- Self cleavage N-ter polyprotein (Peptidase C6) [HC-pro]
- Polyprotein protease (Peptidase C4) [Nla-pro]
REPLICATION
CYTOPLASMIC
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- The viral RNA is translated to produce a polyprotein which is processed by viral proteases into the RdRp protein and structural proteins.
- Replication takes place in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
- Virus assembly in the cytoplasm.
- Viral movement protein P3N-PIPO probably mediates virion cell-to-cell transfer.