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

Xiaofeng Zhang,Xiaofei Zhao,Yanjing Zhang,Yongliang Zhang,Feng Qu,Jialin Yu,Chenggui Han,Dawei Li,Shaofang Niu

doi:10.1186/1743-422x-10-200

Xiaofeng Zhang, Xiaofei Zhao + Show 7 more

Open Access

https://doi.org/10.1186/1743-422x-10-200

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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.

Highlights

Beet black scorch virus (BBSV) is a small single-stranded, positive-sense RNA plant virus belonging to the genus Necrovirus, family Tombusviridae
Replication of BBSV RNA was not appreciably compromised by the set of mutations created in this study In a previous study, we have identified a motif rich in K and R residues, 4KRNKGGKKSR13, in the N terminus of BBSV capsid protein (CP) that mediated the nuclear localization of CP, leading to the speculation that this K/R-rich motif could play an important role in BBSV long distance movement and symptom development [19]
To first determine whether these changes compromised the replication of BBSV genomic RNA (gRNA), we subjected these mutants to single cell infections in N. benthamiana protoplasts

Summary

Introduction

Beet 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. One of the primary functions of CPs is to form virus particles that protect the corresponding viral genomes from degradation by nucleases in the infected host cells, and ensure the successful transmission of viruses between hosts. The interaction between CP and genomic RNA plays a key role in ensuring the specificity of virion assembly and the. The genus Necrovirus of Family Tombusviridae encompasses some of the smallest (+) RNA viruses with monopartite genomes and icosahedral virion symmetry. The functional role of basic amino acid residues in this region is still poorly understood

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