Potyvirus HcPro Suppressor of RNA Silencing Induces PVY Superinfection Exclusion in a Strain-Specific Manner

The potyvirus helper component proteinase (HcPro) is a multifunctional protein, with one of its most documented functions being host antiviral RNA silencing suppression. This study shows that the HcPro of potato virus Y (PVY), an important member of the potyvirus group, prevents the replication of a related competing secondary virus. This phenomenon, referred to as superinfection exclusion (SIE), is common in bacterial, human, and plant virus infections. We also report that HcPro's induction of SIE is strain-specific and that this specificity is provided by the first four amino acid residues of the protein. Consistent with the mechanism of SIE, the study found that HcPro does not exclude a resident virus. Additionally, HcPro's induction of SIE was observed to function independently of its ability to suppress antiviral RNA silencing. HcPro's induction of SIE is relevant given the prevalence of multiple PVY strains that routinely co-infect the same cell and that may lead to recombination and emergence of new and more virulent strains. Furthermore, cross-protection or systemic acquired resistance (SAR) that is employed in plant virus disease management occurs when SIE moves from the cellular level and spreads systemically, emphasizing the importance of studying SIE.