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

Virion RNA is infectious and serves as both the genome and viral messenger RNA. The genomic RNA is translated into polyproteins by VPG-EIF4 Viral initiation of translation. The polyproteins are then processed into functional products by the action of three viral-encoded proteinases. 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 .