The helper-component protease transmission factor of tobacco etch potyvirus binds specifically to an aphid ribosomal protein homologous to the laminin receptor precursor

Abstract

Potyviruses are plant pathogens transmitted by aphids in a non-persistent manner. During transmission, the virus-encoded factor helper-component protease (HCPro) is presumed to act as a molecular bridge, mediating the reversible retention of virions to uncharacterized binding sites in the vector mouthparts. Whilst the predicted interaction between HCPro and the coat protein (CP) of virions has been confirmed experimentally, the characterization of putative HCPro-specific receptors in aphids has remained elusive, with the exception of a report that described binding of HCPro of zucchini yellow mosaic virus to several cuticle proteins. To identify other aphid components that could play a role during transmission, this study used purified HCPro of tobacco etch virus (TEV) in far-Western blotting assays as bait to select interactors among proteins extracted from aphid heads. With this approach, new HCPro-interacting proteins were found, and several were identified after mass spectrometry analysis and searches in databases dedicated to aphid sequences. Among these interactors, a ribosomal protein S2 (RPS2) was chosen for further investigation due to its homology with the laminin receptor precursor, known to act as the receptor of several viruses. The specific interaction between RPS2 and TEV HCPro was confirmed after cloning and heterologous expression of the corresponding Myzus persicae gene. The possible involvement of RPS2 in the transmission process was further suggested by testing a variant of HCPro that was non-functional for transmission due to a mutation in the conserved KITC motif (EITC variant). This variant retained its ability to bind CP but failed to interact with RPS2. INTRODUCTIONNatural dissemination of most plant viruses is mediated by insect vectors, in either circulative or non-circulative processes, with aphids (Hemiptera, Aphididae) being the most common vectors (Pirone & Perry, 2002;Ng & Falk, 2006;Hogenhout et al., 2008). Whilst the viral components implicated in transmission are frequently well known, there is substantially less knowledge about the insect counterparts, and only a few published studies have identified insect products with the capacity to interact with virions or viral components that might play a role in plant virus transmission. Using far-Western blotting or similar methodologies, studies with circulative plant viruses have found proteins interacting with virions at key points of the pathways followed by these viruses inside their insect vectors. Examples include a thrips-transmitted tospovirus (Medeiros et al., 2000) and several aphid-transmitted members of the family Luteoviridae (van den Heuvel et al., 1997;Li et al., 2001;Seddas et al., 2004). A promising approach for further advances in this field is represented by the recent adoption of combined genetic and proteomic tools in the analysis of vector specificity in luteovirids (Yang et al., 2008).In the case of non-circulative plant viruses, the insect vector factors implicated in transmission remain largely unknown. The ...

Bean Common Mosaic Virus and Bean Common Mosaic Necrosis Virus

“…However, a Myzus persicae protein (MpRPS2) with homology to a ribosomal protein has been shown to bind TEV HC-Pro but not to a mutant HC-Pro with a modified KITC domain (Fernández-Calvino et al, 2010) and four potential interacting Myzus persicae proteins were found for the HC-Pro of ZYMV (which like the HC-Pro factors of BCMV and BCMNV has a KLSC sequence) (Dombrovsky et al, 2007).…”

Regulation of Ribosomal Proteins on Viral Infection

“…Besides, HCpro is also a vector transmission helper factor, mediating the retention of virions to aphid mouthparts. In the process, RPS2, as the potential laminin receptor precursor, binds HCpro of TEV to assist virus transmission [91].…”

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

“…Finally, other aspects that remain to be determined in order to better understand the role of HCPro in transmission include the stoichiometry and geometry of the reversible virion-HCPro-vector interactions, which seem to involve multimers of HCPro (Plisson et al, 2003;Ruiz-Ferrer et al, 2005), and the location of this factor at one end of the viral particles (Torrance et al, 2006). Curiously, the visualization of virions within insect stylets has only been attempted and achieved with potyviruses in a very reduced number of studies (Wang et al, 1996), and only a few attempts to discover the vector receptors have been pursued and communicated (Dombrovsky et al, 2007;Fern andez-Calvino et al, 2010). Thus, at this point, it is still uncertain whether the potyvirusspecific aphid receptor co-localizes or shares properties with the putative receptors of viruses from other families (Blanc et al, 2014;Uzest et al, 2007).…”