Did Silencing Suppression Counter-Defensive Strategy Contribute to Origin and Evolution of the Triple Gene Block Coding for Plant Virus Movement Proteins?

TGBp1, TGBp2, and TGBp3, three plant virus movement proteins encoded by the “triple gene block” (TGB), may act in concert to facilitate cell-to-cell transport of viral RNA genomes. Transient expression of Potato mop-top virus (genus Pomovirus) movement proteins was used as a model to reconstruct interactions between TGB proteins. In bombarded epidermal cells of Nicotiana benthamiana, green fluorescent protein (GFP)-TGBp1 was distributed uniformly. However, in the presence of TGBp2 and TGBp3, GFP-TGBp1 was directed to intermediate bodies at the cell periphery, and to cell wall-embedded punctate bodies. Moreover, GFP-TGBp1 migrated into cells immediately adjacent to the bombarded cell. These data suggest that TGBp2 and TGBp3 mediate transport of GFP-TGBp1 to and through plasmodesmata. Mutagenesis of TGBp1 suggested that the NTPase and helicase activities of TGBp1 were not required for its transport to intermediate bodies directed by TGBp2 and TGBp3, but these activities were essential for the protein association with cell wall-embedded punctate bodies and translocation of TGBp1 to neighboring cells. The C-terminal region of TGBp1 was critical for trafficking mediated by TGBp2 and TGBp3. Mutation analysis also suggested an involvement of the TGBp2 C-terminal region in interactions with TGBp1.

Download Full-text

Replication and trafficking of a plant virus are coupled at the entrances of plasmodesmata

The Journal of Cell Biology ◽

10.1083/jcb.201304003 ◽

2013 ◽

Vol 201 (7) ◽

pp. 981-995 ◽

Cited By ~ 92

Author(s):

Jens Tilsner ◽

Olga Linnik ◽

Marion Louveaux ◽

Ian M. Roberts ◽

Sean N. Chapman ◽

...

Keyword(s):

Plant Virus ◽

Plant Cell Wall ◽

Triple Gene Block ◽

Potato Virus X ◽

Plant Viruses ◽

Viral Coat Protein ◽

Movement Proteins ◽

Gene Block ◽

Replication Sites ◽

Viral Coat

Plant viruses use movement proteins (MPs) to modify intercellular pores called plasmodesmata (PD) to cross the plant cell wall. Many viruses encode a conserved set of three MPs, known as the triple gene block (TGB), typified by Potato virus X (PVX). In this paper, using live-cell imaging of viral RNA (vRNA) and virus-encoded proteins, we show that the TGB proteins have distinct functions during movement. TGB2 and TGB3 established endoplasmic reticulum–derived membranous caps at PD orifices. These caps harbored the PVX replicase and nonencapsidated vRNA and represented PD-anchored viral replication sites. TGB1 mediated insertion of the viral coat protein into PD, probably by its interaction with the 5′ end of nascent virions, and was recruited to PD by the TGB2/3 complex. We propose a new model of plant virus movement, which we term coreplicational insertion, in which MPs function to compartmentalize replication complexes at PD for localized RNA synthesis and directional trafficking of the virus between cells.

Download Full-text

Recent Advances in Research of Plant Virus Movement Mediated by Triple Gene Block

Frontiers in Plant Science ◽

10.3389/fpls.2012.00276 ◽

2012 ◽

Vol 3 ◽

Cited By ~ 20

Author(s):

Andrey G. Solovyev ◽

Natalia O. Kalinina ◽

Sergey Y. Morozov

Keyword(s):

Plant Virus ◽

Triple Gene Block ◽

Virus Movement ◽

Gene Block ◽

Recent Advances

Download Full-text

Triple gene block: modular design of a multifunctional machine for plant virus movement

Journal of General Virology ◽

10.1099/vir.0.18922-0 ◽

2003 ◽

Vol 84 (6) ◽

pp. 1351-1366 ◽

Cited By ~ 247

Author(s):

Sergey Yu. Morozov ◽

Andrey G. Solovyev

Keyword(s):

Plant Virus ◽

Modular Design ◽

Triple Gene Block ◽

Virus Movement ◽

Gene Block

Download Full-text

Molecular biology of potexviruses: recent advances

Journal of General Virology ◽

10.1099/vir.0.82667-0 ◽

2007 ◽

Vol 88 (6) ◽

pp. 1643-1655 ◽

Cited By ~ 109

Author(s):

Jeanmarie Verchot-Lubicz ◽

Chang-Ming Ye ◽

Devinka Bamunusinghe

Keyword(s):

Gene Silencing ◽

Rna Synthesis ◽

Triple Gene Block ◽

Potato Virus X ◽

Future Research ◽

Virus Movement ◽

Suppressor Activity ◽

Gene Block ◽

Recent Advances

Recent advances in potexvirus research have produced new models describing virus replication, cell-to-cell movement, encapsidation, R gene-mediated resistance and gene silencing. Interactions between distant RNA elements are a central theme in potexvirus replication. The 5′ non-translated region (NTR) regulates genomic and subgenomic RNA synthesis and encapsidation, as well as virus plasmodesmal transport. The 3′ NTR regulates both plus- and minus-strand RNA synthesis. How the triple gene-block proteins interact for virus movement is still elusive. As the potato virus X (PVX) TGBp1 protein gates plasmodesmata, regulates virus translation and is a suppressor of RNA silencing, further research is needed to determine how these properties contribute to propelling virus through the plasmodesmata. Specifically, TGBp1 suppressor activity is required for virus movement, but how the silencing machinery relates to plasmodesmata is not known. The TGBp2 and TGBp3 proteins are endoplasmic reticulum (ER)-associated proteins required for virus movement. TGBp2 associates with ER-derived vesicles that traffic along the actin network. Future research will determine whether the virus-induced vesicles are cytopathic structures regulating events along the ER or are vehicles carrying virus to the plasmodesmata for transfer into neighbouring cells. Efforts to assemble virions in vitro identified a single-tailed particle (STP) comprising RNA, coat protein (CP) and TGBp1. It has been proposed that TGBp1 aids in transport of virions or STP between cells and ensures translation of RNA in the receiving cells. PVX is also a tool for studying Avr–R gene interactions and gene silencing in plants. The PVX CP is the elicitor for the Rx gene. Recent reports of the PVX CP reveal how CP interacts with the Rx gene product.

Download Full-text

The Potato Virus X TGBp2 Protein Plays Dual Functional Roles in Viral Replication and Movement

Journal of Virology ◽

10.1128/jvi.01635-18 ◽

2018 ◽

Vol 93 (5) ◽

Cited By ~ 2

Author(s):

Xiaoyun Wu ◽

Jiahui Liu ◽

Mengzhu Chai ◽

Jinhui Wang ◽

Dalong Li ◽

...

Keyword(s):

Triple Gene Block ◽

Potato Virus X ◽

Plant Viruses ◽

Open Reading Frames ◽

Movement Proteins ◽

Gene Block ◽

Functional Roles ◽

Viral Rdrp ◽

Dual Functional ◽

Intercellular Movement

ABSTRACTPlant viruses usually encode one or more movement proteins (MP) to accomplish their intercellular movement. A group of positive-strand RNA plant viruses requires three viral proteins (TGBp1, TGBp2, and TGBp3) that are encoded by an evolutionarily conserved genetic module of three partially overlapping open reading frames (ORFs), termed the triple gene block (TGB). However, how these three viral movement proteins function cooperatively in viral intercellular movement is still elusive. Using a novelin vivodouble-stranded RNA (dsRNA) labeling system, we showed that the dsRNAs generated by potato virus X (PVX) RNA-dependent RNA polymerase (RdRp) are colocalized with viral RdRp, which are further tightly covered by “chain mail”-like TGBp2 aggregates and localizes alongside TGBp3 aggregates. We also discovered that TGBp2 interacts with the C-terminal domain of PVX RdRp, and this interaction is required for the localization of TGBp3 and itself to the RdRp/dsRNA bodies. Moreover, we reveal that the central and C-terminal hydrophilic domains of TGBp2 are required to interact with viral RdRp. Finally, we demonstrate that knockout of the entire TGBp2 or the domain involved in interacting with viral RdRp attenuates both PVX replication and movement. Collectively, these findings suggest that TGBp2 plays dual functional roles in PVX replication and intercellular movement.IMPORTANCEMany plant viruses contain three partially overlapping open reading frames (ORFs), termed the triple gene block (TGB), for intercellular movement. However, how the corresponding three proteins coordinate their functions remains obscure. In the present study, we provided multiple lines of evidence supporting the notion that PVX TGBp2 functions as the molecular adaptor bridging the interaction between the RdRp/dsRNA body and TGBp3 by forming “chain mail”-like structures in the RdRp/dsRNA body, which can also enhance viral replication. Taken together, our results provide new insights into the replication and movement of PVX and possibly also other TGB-containing plant viruses.

Download Full-text

P42 Movement Protein of Beet necrotic yellow vein virus Is Targeted by the Movement Proteins P13 and P15 to Punctate Bodies Associated with Plasmodesmata

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2000.13.5.520 ◽

2000 ◽

Vol 13 (5) ◽

pp. 520-528 ◽

Cited By ~ 59

Author(s):

M. Erhardt ◽

M. Morant ◽

C. Ritzenthaler ◽

C. Stussi-Garaud ◽

H. Guilley ◽

...

Keyword(s):

Cell Wall ◽

Fluorescent Protein ◽

Triple Gene Block ◽

Point Mutations ◽

Cell Movement ◽

Leading Edge ◽

Yellow Vein ◽

Body Formation ◽

Movement Proteins ◽

Gene Block

Cell-to-cell movement of Beet necrotic yellow vein virus (BNYVV) is driven by a set of three movement proteins—P42, P13, and P15—organized into a triple gene block (TGB) on viral RNA 2. The first TGB protein, P42, has been fused to the green fluorescent protein (GFP) and fusion proteins between P42 and GFP were expressed from a BNYVV RNA 3-based replicon during virus infection. GFP-P42, in which the GFP was fused to the P42 N terminus, could drive viral cell-to-cell movement when the copy of the P42 gene on RNA 2 was disabled but the C-terminal fusion P42-GFP could not. Confocal microscopy of epidermal cells of Chenopodium quinoa near the leading edge of the infection revealed that GFP-P42 localized to punctate bodies apposed to the cell wall whereas free GFP, expressed from the replicon, was distributed uniformly throughout the cytoplasm. The punctate bodies sometimes appeared to traverse the cell wall or to form pairs of disconnected bodies on each side. The punctate bodies co-localized with callose, indicating that they are associated with plasmodesmata-rich regions such as pit fields. Point mutations in P42 that inhibited its ability to drive cell-to-cell movement also inhibited GFP-P42 punctate body formation. GFP-P42 punctate body formation was dependent on expression of P13 and P15 during the infection, indicating that these proteins act together or sequentially to localize P42 to the plasmodesmata.

Download Full-text