Potyvirus

VIRION

Non-enveloped, flexuous, filamentous, of 720-850 nm long and 12-15 nm in diameter. Symmetry helical. Presence of characteristic inclusion bodies within infected plant cells.

GENOME

Monopartite, linear, ssRNA(+) genome of 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 is translated into polyproteins which are subsequently processed by the action of three viral-encoded proteinases into functional products. P3N-PIPO is expressed by polymerase slippage mechanism from the P3 ORF and probably acts as a movement protein .

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 a polyprotein which is processed by viral proteases into the RdRp protein and structural proteins.
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. Virus assembly in the cytoplasm.
7. Viral movement protein P3N-PIPO probably mediates virion cell-to-cell transfer.

Host-virus interaction

Suppression of RNA silencing

Potyviruses HC-PRO functions as a suppressor of RNA silencing .

Suppression of other plant defenses

VPg is a potent inhibitor of PAP depurination of RNA, thereby suppressing one of the plant defense mechanisms .