N-terminal basic amino acid residues of Beet black scorch virus capsid protein play a critical role in virion assembly and systemic movement

Abstract

BackgroundBeet black scorch virus (BBSV) is a small single-stranded, positive-sense RNA plant virus belonging to the genus Necrovirus, family Tombusviridae. Its capsid protein (CP) contains a 13 amino acid long basic region at the N-terminus, rich in arginine and lysine residues, which is thought to interact with viral RNA to initiate virion assembly.ResultsIn the current study, a series of BBSV mutants containing amino acid substitutions as well as deletions within the N-terminal region were generated and examined for their effects on viral RNA replication, virion assembly, and long distance spread in protoplasts and whole host plants of BBSV. The RNA-binding activities of the mutated CPs were also evaluated in vitro. These experiments allowed us to identify two key basic amino acid residues in this region that are responsible for initiating virus assembly through RNA-binding. Proper assembly of BBSV particles is in turn needed for efficient viral systemic movement.ConclusionsWe have identified two basic amino acid residues near the N-terminus of the BBSV CP that bind viral RNA with high affinity to initiate virion assembly. We further provide evidence showing that systemic spread of BBSV in infected plants requires intact virions. This study represents the first in-depth investigation of the role of basic amino acid residues within the N-terminus of a necroviral CP.

Hijacking of the nucleolar protein fibrillarin by TGB1 is required for cell‐to‐cell movement of Barley stripe mosaic virus

“…The Cucumber mosaic virus (CMV) 2b silencing suppressor protein is targeted to the nucleolus by NLS1 and NLS2, and deletion of either one or both signals abolishes 2b local suppression of silencing (Gonz alez et al, 2010). Mutation of the CP NLS also abolishes BBSV transit to upper non-inoculated leaves (Zhang et al, , 2013. It is also relevant that nucleolar localization of GRV ORF3 is essential for the formation of viral RNPs and for systemic movement (Kim et al, 2007b).…”

Turnip mosaic virus Moves Systemically through Both Phloem and Xylem as Membrane-Associated Complexes

“…This assumption is based on the observation that Coat Protein (CP) deletions debilitating virus assembly prevent systemic infection (Brault et al, 2003;Zhang et al, 2013;Hipper et al, 2014). Some investigations showed the actual presence of virions in sieve elements.…”

Hibiscus Chlorotic Ringspot Virus Coat Protein Is Essential for Cell-to-Cell and Long-Distance Movement but Not for Viral RNA Replication

“…This result shows that absence of the virions in mutant 2776 (C to G) is not due to the relative high pH used for virion purification which may render in less stable virions. In BBSV, the CP was detected but not the virions in the purified virion samples isolated from a CP N-ARM mutant BM5 inoculated plants and the authors postulated that it was due to lower level of virion assembly [65] . In this study, despite exhaustive search for virions, there is still no evidence to show that lack of virions in proline 63 mutant inoculated plants is due to low level of virion assembly.…”

“…In TCV, its CP plays a host-dependent role in the virus long-distance movement [37] , [45] , [63] , [64] . The proper virion assembly in Beet black scorch virus (BBSV) is needed for the virus systemic movement [65] . In Olive latent virus 1 , the CP C-terminal mutants could form intact virions but its systemic movement was not detected, indicating that virion formation is necessary but not sufficient for long-distance movement [66] .…”