The HCPro from the Potyviridae family: an enviable multitasking Helper Component that every virus would like to have

Abstract

RNA viruses have very compact genomes and so provide a unique opportunity to study how evolution works to optimize the use of very limited genomic information. A widespread viral strategy to solve this issue concerning the coding space relies on the expression of proteins with multiple functions. Members of the family Potyviridae, the most abundant group of RNA viruses in plants, offer several attractive examples of viral factors which play roles in diverse infection-related pathways. The Helper Component Proteinase (HCPro) is an essential and well-characterized multitasking protein for which at least three independent functions have been described: (i) viral plant-to-plant transmission; (ii) polyprotein maturation; and (iii) RNA silencing suppression. Moreover, multitudes of host factors have been found to interact with HCPro. Intriguingly, most of these partners have not been ascribed to any of the HCPro roles during the infectious cycle, supporting the idea that this protein might play even more roles than those already established. In this comprehensive review, we attempt to summarize our current knowledge about HCPro and its already attributed and putative novel roles, and to discuss the similarities and differences regarding this factor in members of this important viral family.

First evidence of the occurrence of Turnip mosaic virus in Ukraine and molecular characterization of its isolate

“…Interestingly, these recombinants generally had Asian‐BR sequences not only in the P3–CI genomic region but also in the HC‐Pro gene (Nguyen et al., ; Ohshima, Akaishi, Kajiyama, Koga, & Gibbs, ; Ohshima et al., ; Tomitaka & Ohshima, ; Yasaka et al., , ). The latter gene is known to be an RNA silencing suppressor of potyviruses (Valli, Gallo, Rodamilans, López‐Moya, & García, ). In this study, we found a novel interlineage recombination type pattern of world‐B and Asian‐BR group parents (between nt 1374 and 1375).…”

A Functional Link between RNA Replication and Virion Assembly in the Potyvirus Plum Pox Virus

“…HCPro was first recognized as a helper component required for aphid transmission of viral particles (21,22). Later on, a large number of additional activities were assigned to HCPro (23), although the most important one appears to be the suppression of antiviral RNA silencing (24,25), as a potyvirus expressing an HCPro without RNA silencing suppression activity is not viable in wild-type plants but can infect RNA silencing-deficient plants (26). Furthermore, in line with this assumption, chimeric viruses in which HCPro was replaced by diverse heterologous RNA silencing suppressors (RSSs) are infectious in RNA silencing-proficient plants (27,28).…”

Barley stripe mosaic virus infection requires PKA‐mediated phosphorylation of γb for suppression of both RNA silencing and the host cell death response

“…Since S96A could not suppress RNA silencing, we wondered if the overexpression of other VSRs could suppress the BSMV S96A induced cell death response. We chose four well‐studied VSRs, including TBSV p19 (Lakatos et al ., ), Tobacco etch virus (TEV) HC‐pro (Valli et al ., ), Cucumber mosaic virus (CMV) 2b (Duan et al ., ), and Turnip crinkle virus (TCV) p38 (Thomas et al ., ). These VSRs were overexpressed with WT BSMV or BSMV S96A inoculated via agroinfiltration.…”

“…Viral suppressors of RNA silencing (VSRs), including potyvirus HC‐pro (Urcuqui‐Inchima et al ., ; Valli et al ., ), Cucumber mosaic virus (CMV) 2b (Lewsey et al ., ), geminivirus βC1 (Cui et al ., ; Yang et al ., ; Zhang et al ., ; Zhong et al ., ), Barley strip mosaic virus (BSMV) γb (Yelina et al ., ; Bragg et al ., ; K. Zhang et al ., ), and Cauliflower mosaic virus (CaMV) P6 (Love et al ., ; Schoelz et al ., ), often have multiple functions in addition to RNA silencing suppression. A common and intriguing feature of viral proteins is their involvement in disease symptom development.…”