Structure of Turnip mosaic virus and its viral-like particles

Abstract

Turnip mosaic virus (TuMV), a potyvirus, is a flexible filamentous plant virus that displays a helical arrangement of coat protein copies (CPs) bound to the ssRNA genome. TuMV is a bona fide representative of the Potyvirus genus, one of most abundant groups of plant viruses, which displays a very wide host range. We have studied by cryoEM the structure of TuMV virions and its viral-like particles (VLPs) to explore the role of the interactions between proteins and RNA in the assembly of the virions. The results show that the CP-RNA interaction is needed for the correct orientation of the CP N-terminal arm, a region that plays as a molecular staple between CP subunits in the fully assembled virion.

The cis‐expression of the coat protein of turnip mosaic virus is essential for viral intercellular movement in plants

“…To examine if CP provided in trans could rescue the movement defect of TuMV CP deletion or point-mutation mutants, we generated transgenic Arabidopsis plants overexpressing TuMV CP and then inoculated them with the movement-defective TuMV CP mutants. We confirmed CP expression in these plants ( Figure 7), and observed VLPs in these transgenic plants, in agreement with recently published data (Cuesta et al, 2019). To our surprise, we found that overexpression of CP failed to rescue these movement-defective mutants (Figure 7).…”

“…Considering that the fluorescent protein tag might negatively affect the CP interactome and virion assembly in plants, we chose the plant expression vector pEarleyGate100 (Early et al, 2006), which contains no fluorescent protein tag, to generate the CP expression vector for genetic transformation of Arabidopsis. After confirmation of the expression of the TuMV CP by immunoblotting and RT-PCR (Figure 7a), we observed virus-like particles (VLPs) with various lengths in those CP-expressing transgenic plants, consistent with a recent report (Cuesta et al, 2019).…”

“…The TuMV CP comprises 288 amino acid residues with a molecular mass of approximately 33 kDa. Based on the recently released atomic model (PDB: 6T34) (Cuesta et al, 2019), TuMV CP is divided into the N-terminus (N, amino acids 1-97), core (amino acids 98-245), and C-terminus (C, amino acids 246-288) domains (Figure 1b). To identify the CP segments that are essential for TuMV cell-to-cell movement, we created four partial CP deletion mutants using the parental WT virus (pCBTuMV-GFP//mCherry) ( Figure 1b and Table 2).…”

“…It seems that the requirement of the variable N domain (at least its N-terminal segment) for cell-to-cell movement and systemic infection of the viruses in the Potyviridae family may vary from virus to virus. It is worth mentioning that the atomic structure-based definition of the N, core, and C domains of potyviral CPs was not done until recently (Zamora et al, 2017;Cuesta et al, 2019;Kezar et al, 2019). Previously, the C-terminal segment of the N domain was included in the core domain.…”

“…The potyviral CP encompasses a variable N-terminal domain exposed on the virion surface that is susceptible to trypsin treatment, a conserved core domain that interacts with viral RNA and forms the core subunit structure of the virion, and a C-terminal domain that has been implicated in CP-vRNA binding (Zamora et al, 2017;Cuesta et al, 2019;Kezar et al, 2019). Deletion of CP or its important domains or mutation of key charged residues within these domains abolishes potyvirus intercellular movement or systemic infection (Dolja et al, 1994(Dolja et al, , 1995Seo et al, 2013;Kezar et al, 2019).…”