Molecular biology of potexviruses: recent advances

Verchot, Jeanmarie; Ye, Changming; Bamunusinghe, Devinka

doi:10.1099/vir.0.82667-0

Cited by 142 publications

(91 citation statements)

References 125 publications

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“…Previous studies have examined intracellular localization and interactions of the TGB proteins of several potexviruses through expression of individual gene fusion constructs by biolistic delivery to epidermal cells or expression from modified viral genomes (reviewed by Morozov & Solovyev, 2003;Verchot-Lubicz, 2005;Verchot-Lubicz et al, 2007). In contrast, we have utilized Agrobacterium-mediated infiltration to deliver TGB fusion constructs throughout the leaf, and, in confirmatory experiments, expressed AltMV TGB3 variants as additional genes from both AltMV and PVX infectious clones.…”

Section: Discussionmentioning

confidence: 99%

“…Despite this body of work, 'a full understanding of the specific requirement of TGB3 and the functional interchangeability of TGB3 among different potexviruses for intercellular movement remains elusive' (Lin et al, 2006). The 8 kDa PVX TGB3 is an ER-binding protein with a single, N-terminal transmembrane domain (Morozov & Solovyev, 2003;Verchot-Lubicz et al, 2007), and TGB2 and TGB3 are reported to co-localize (Ju et al, 2008;Solovyev et al, 2000). PVX TGB3 interacts with the ER network and is associated with granular vesicles induced by TGB2 (Samuels et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Viral genomes encode proteins that have evolved to achieve these functions (Leisner & Howell, 1993;Lucas, 2006;Verchot-Lubicz et al, 2007). Research on the mechanisms of plant virus movement has provided insight into the interactions that must occur with the host for the virus to move into adjacent cells (Boevink & Oparka, 2005;Lucas, 2006;Waigmann et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

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Mutation of a chloroplast-targeting signal in Alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement

Lim¹,

Vaira²,

Bae

et al. 2010

Journal of General Virology

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Cell-to-cell movement of potexviruses requires coordinated action of the coat protein and triple gene block (TGB) proteins. The structural properties of Alternanthera mosaic virus (AltMV) TGB3 were examined by methods differentiating between signal peptides and transmembrane domains, and its subcellular localization was studied by Agrobacterium-mediated transient expression and confocal microscopy. Unlike potato virus X (PVX) TGB3, AltMV TGB3 was not associated with the endoplasmic reticulum, and accumulated preferentially in mesophyll cells. Deletion and sitespecific mutagenesis revealed an internal signal VL(17,18) of TGB3 essential for chloroplast localization, and either deletion of the TGB3 start codon or alteration of the chloroplastlocalization signal limited cell-to-cell movement to the epidermis, yielding a virus that was unable to move into the mesophyll layer. Overexpression of AltMV TGB3 from either AltMV or PVX infectious clones resulted in veinal necrosis and vesiculation at the chloroplast membrane, a cytopathology not observed in wild-type infections. The distinctive mesophyll and chloroplast localization of AltMV TGB3 highlights the critical role played by mesophyll targeting in virus longdistance movement within plants.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mutation of a chloroplast-targeting signal in Alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement

Lim¹,

Vaira²,

Bae

et al. 2010

Journal of General Virology

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“…PVX is the type member of the Potexvirus family of viruses (Verchot-Lubicz et al, 2007). Although the PVX VSR, P25, destabilizes Arabidopsis AGO1, this virus does not normally systemically infect Arabidopsis Columbia-0 (Col-0) (Chiu et al, 2010;Jaubert et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Functional and Genetic Analysis Identify a Role for Arabidopsis ARGONAUTE5 in Antiviral RNA Silencing

2015

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RNA silencing functions as an antiviral defense through the action of DICER-like (DCL) and ARGONAUTE (AGO) proteins. In turn, plant viruses have evolved strategies to counteract this defense mechanism, including the expression of suppressors of RNA silencing. Potato virus X (PVX) does not systemically infect Arabidopsis thaliana Columbia-0, but is able to do so effectively in mutants lacking at least two of the four Arabidopsis DCL proteins. PVX can also infect Arabidopsis ago2 mutants, albeit less effectively than double DCL mutants, suggesting that additional AGO proteins may mediate anti-viral defenses. Here we show, using functional assays, that all Arabidopsis AGO proteins have the potential to target PVX lacking its viral suppressor of RNA silencing (VSR), P25, but that only AGO2 and AGO5 are able to target wild-type PVX. However, P25 directly affects only a small subset of AGO proteins, and we present evidence indicating that its protective effect is mediated by precluding AGO proteins from accessing viral RNA, as well as by directly inhibiting the RNA silencing machinery. In agreement with functional assays, we show that Potexvirus infection induces AGO5 expression and that both AGO2 and AGO5 are required for full restriction of PVX infection in systemic tissues of Arabidopsis.

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“…Members of the genus Potexvirus have a monopartite, positive-strand RNA genome containing five open reading frames (ORFs) (Verchot-Lubicz et al, 2007). ORF1 encodes a viral replicase and ORF5 encodes a coat protein (CP).…”

Section: Introductionmentioning

confidence: 99%

Variability in the level of RNA silencing suppression caused by triple gene block protein 1 (TGBp1) from various potexviruses during infection

Senshu

Ozeki

Komatsu

et al. 2009

Journal of General Virology

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RNA silencing is an important defence mechanism against virus infection, and many plant viruses encode RNA silencing suppressors as a counter defence. In this study, we analysed the RNA silencing suppression ability of multiple virus species of the genus Potexvirus. Nicotiana benthamiana plants exhibiting RNA silencing of a green fluorescent protein (GFP) transgene showed reversal of GFP fluorescence when systemically infected with potexviruses. However, the degree of GFP fluorescence varied among potexviruses. Agrobacterium-mediated transient expression assay in N. benthamiana leaves demonstrated that the triple gene block protein 1 (TGBp1) encoded by these potexviruses has drastically different levels of silencing suppressor activity, and these differences were directly related to variations in the silencing suppression ability during virus infection. These results suggest that suppressor activities differ even among homologous proteins encoded by viruses of the same genus, and that TGBp1 contributes to the variation in the level of RNA silencing suppression by potexviruses. Moreover, we investigated the effect of TGBp1 encoded by Plantago asiatica mosaic virus (PlAMV), which exhibited a strong suppressor activity, on the accumulation of microRNA, virus genomic RNA and virus-derived small interfering RNAs. INTRODUCTIONRNA silencing is an RNA-guided gene regulatory mechanism that operates in a wide variety of eukaryotic organisms. RNA silencing begins with processing of an RNA trigger into small RNAs (~21-30 nt) by the RNase III-type enzyme Dicer (Bernstein et al., 2001). In plants, small RNAs are divided into two classes: small interfering RNAs (siRNAs) and microRNAs (miRNAs) (Mallory & Vaucheret, 2006;Brodersen & Voinnet, 2006). siRNAs are generated from double-stranded RNAs (dsRNAs) which are usually derived from transgenes, viruses or endogenous non-coding RNA genes. On the other hand, miRNAs are generated from genome-encoded precursor RNAs with imperfect stem-loop structures. These small RNAs are then incorporated into multicomponent RNA-induced silencing complexes (RISC), which contain an Argonaute (AGO) family protein and lead to homologous RNA cleavage or translational repression, and (or) DNA/chromatin methylation (Hammond, 2005;Xie et al., 2004;Chapman & Carrington, 2007).One of the important roles of RNA silencing in plants is antiviral defence (Ratcliff et al., 1997;Vance & Vaucheret, 2001;Baulcombe, 2004;Ding & Voinnet, 2007). During virus infection, dsRNAs derived from viral replication intermediates or highly structured viral genomic RNAs trigger RNA silencing directed against the viruses. Consequently, initially symptomatic plants recover from infection and become resistant to secondary infection with homologous viruses. To counteract RNA silencing, viruses have evolved RNA silencing suppressors. More than 40 RNA silencing suppressors have been identified in plant, animal, insect and fungal viruses (Li & Ding, 2006). These suppressors do not have obvious sequence similarity to one another, and t...

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Molecular biology of potexviruses: recent advances

Cited by 142 publications

References 125 publications

Mutation of a chloroplast-targeting signal in Alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement

Mutation of a chloroplast-targeting signal in Alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement

Functional and Genetic Analysis Identify a Role for Arabidopsis ARGONAUTE5 in Antiviral RNA Silencing

Variability in the level of RNA silencing suppression caused by triple gene block protein 1 (TGBp1) from various potexviruses during infection

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