The Potyviridae P1a leader protease contributes to host range specificity

Abstract

The P1a protein of the ipomovirus Cucumber vein yellowing virus is one of the self-cleavage serine proteases present in Potyviridae family members. P1a is located at the N-terminal end of the viral polyprotein, and is closely related to potyviral P1 protease. For its proteolytic activity, P1a requires a still unknown host factor; this might be linked to involvement in host specificity. Here we built a series of constructs and chimeric viruses to help elucidate the role of P1a cleavage in host range definition. We demonstrate that host-dependent separation of P1a from the remainder of the polyprotein is essential for suppressing RNA silencing defenses and for efficient viral infection. These findings support the role of viral proteases as important determinants in host adaptation.

Truncation of a P1 leader proteinase facilitates potyvirus replication in a non‐permissive host

“…One of the aspects limiting host–potyvirid compatibility may be the absence of an appropriate plant cofactor for P1 release from the rest of the polyprotein. In agreement with this view, replacement of P1 by CVYV P1a facilitated local infection of PPV in cucumber (Carbonell et al ., ; Shan et al ., ). To address the capacity of P1Pro to overcome host‐specific restrictions to viral infection, C. sativus plants were agroinoculated with wild‐type PPV or the viral clone PPV‐P1Pro, in which the N‐terminal antagonistic domain of P1 was deleted (Fig.…”

“…The data presented in this article support a view in which P1 leader proteases are, at least in part, responsible for the narrow host ranges of potyvirid species and the driving forces of Potyviridae speciation, as suggested previously (Desbiez and Lecoq, ; Maliogka et al ., ; Rodamilans et al ., ; Salvador et al ., ; Shan et al ., ; Valli et al ., ). We propose that this role is directly dependent on cofactor requirements of P1 processing and thus the release of functional silencing suppressors to counteract host antiviral defences (Fig.…”

“…It harbours a serine protease domain responsible for cis-cleavage at the P1-HC junction, and thus P1 self-releases from the polyprotein (Adams et al, 2005). P1 acts as a non-essential accessory factor (Verchot and Carrington, 1995b), but its detachment from the polyprotein is indispensable for viral viability, as the lack of self-cleavage impairs the functionality of the downstream silencing suppressor HC (Pasin et al, 2014;Shan et al, 2015;Verchot and Carrington, 1995a).…”

“…Inefficient P1 processing impairs HC silencing suppressor activity and viral viability (Pasin et al, 2014;Shan et al, 2015). After in vitro translation experiments, we sought to further characterize PPV P1Pro in planta, assessing how its self-cleavage might affect HC functions.…”

An atypical RNA silencing suppression strategy provides a snapshot of the evolution of sweet potato-infecting potyviruses

“…Classified as a Type A P1 protein, it is the most variable potyviral factor in length and amino acid sequence 14 , 15 . It is a non-essential factor involved in host range definition 15 – 18 , whose protease activity appears to modulate viral replication facilitating the escape from host defenses 19 – 21 . Additional P1 functions, including preferential translation of viral mRNAs, have been suggested 20 , 22 , 23 .…”