The Coat Protein of Citrus Yellow Vein Clearing Virus Interacts with Viral Movement Proteins and Serves as an RNA Silencing Suppressor.

Atta Ur Rehman,Muhammad Waqas,Feng Li,Ni Hong,Zhuoran Li,Guoping Wang,Zuokun Yang,Wenxing Xu

doi:10.3390/v11040329

Atta Ur Rehman, Muhammad Waqas + Show 6 more

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https://doi.org/10.3390/v11040329

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Abstract

Citrus yellow vein clearing virus is a newly accepted member of the genus Mandarivirus in the family Alphaflexiviridae. The triple gene block proteins (TGBp1, TGBp2 and TGBp3) encoded by plant viruses in this family function on facilitating virus movement. However, the protein function of citrus yellow vein clearing virus (CYVCV) have never been explored. Here, we showed in both yeast two-hybrid (Y2H) and bimolecular fluorescence (BiFC) assays that the coat protein (CP), TGBp1 and TGBp2 of CYVCV are self-interacting. Its CP also interacts with all three TGB proteins, and TGBp1 and TGBp2 interact with each other but not with TGBp3. Furthermore, the viral CP colocalizes with TGBp1 and TGBp3 at the plasmodesmata (PD) of epidermal cells of Nicotiana benthamiana leaves, and TGBp1 can translocate TGBp2 from granular-like structures embedded within ER networks to the PD. The results suggest that these proteins could coexist at the PD of epidermal cells of N. benthamiana. Using Agrobacterium infiltration-mediated RNA silencing assays, we show that CYVCV CP is a strong RNA silencing suppressor (RSS) triggered by positive-sense green fluorescent protein (GFP) RNA. The presented results provide insights for further revealing the mechanism of the viral movement and suppression of RNA silencing.

Highlights

A large group of plant viruses possess a triple gene block (TGB) encoding three proteins (TGBp1, TGBp2 and TGBp3) that coordinately function in facilitating cell-to-cell and long-distance movement of plant viruses [1,2,3]
Primers used for the amplification of five open reading frames (ORFs) encoding proteins TGBp1, TGBp2, TGBp3, coat protein (CP), and 23K of citrus yellow vein clearing virus (CYVCV) were designed based on multiple alignments of the viral sequences available in GenBank (Table S1)
96.6–100% identities with the corresponding proteins encoded by other CYVCV isolates available in

Summary

Introduction

A large group of plant viruses possess a triple gene block (TGB) encoding three proteins (TGBp1, TGBp2 and TGBp3) that coordinately function in facilitating cell-to-cell and long-distance movement of plant viruses [1,2,3]. Viruses possessing TGBps have been categorized into two major classes, i.e., hordei-like and potex-like viruses, according to their differences in the mechanism involved in virus movement [4,5,6,7]. Virions of potex-like viruses are filamentous, contain a monopartite RNA genome and need coat protein (CP) for their movement from one cell to another. Viruses 2019, 11, 329 of species in the genera Hordeivirus, Pomovirus, Pecluvirus, and Benyvirus [7] and form rod-shaped virions containing multipartite genomic RNA segments; their CPs are not necessarily involved in viral cell-to-cell movement [8]. Potex-like TGBp1 proteins differ substantially from hordei-like

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