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The ability of PVX p25 to form RL structures in plant cells is necessary for its function in movement, but not for its suppression of RNA silencing.

ABSTRACT: The p25 triple gene block protein of Potato virus X (PVX) is multifunctional, participating in viral movement and acting as a suppressor of RNA silencing. The cell-to-cell movement of PVX is known to depend on the suppression function of p25. GFP-fused p25 accumulates in rod-like (RL) structures with intense fluorescence in cells. By monitoring the location of fluorescence at different times, we have now shown that the RL structure is composed of filaments. P25 mutants without the conditional ability to recover movement function could not form RL structures while the mutants that had the ability did form the structure, suggesting that the ability of p25 to form RL structures is necessary for its function in cell-to-cell movement, but not for its suppressor function. Moreover, chemical inhibition of microfilaments in cells destroyed the formation of the complete RL structure. Additionally, TGBp2 and TGBp3 were recruited into the RL structure, suggesting a relationship between the TGBps in virus movement.

SUBMITTER: Yan F

PROVIDER: S-EPMC3420909 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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The ability of PVX p25 to form RL structures in plant cells is necessary for its function in movement, but not for its suppression of RNA silencing.

Yan Fei F Lu Yuwen Y Lin Lin L Zheng Hongying H Chen Jianping J

PloS one 20120816 8

The p25 triple gene block protein of Potato virus X (PVX) is multifunctional, participating in viral movement and acting as a suppressor of RNA silencing. The cell-to-cell movement of PVX is known to depend on the suppression function of p25. GFP-fused p25 accumulates in rod-like (RL) structures with intense fluorescence in cells. By monitoring the location of fluorescence at different times, we have now shown that the RL structure is composed of filaments. P25 mutants without the conditional ab ...[more]

PMID: 22916231

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Project description:BackgroundRNA silencing affects a broad range of regulatory processes in all eukaryotes ranging from chromatin structure maintenance to transcriptional and translational regulation and longevity of the mRNAs. Particularly in plants, it functions as the major defense mechanism against viruses. To counter-act this defense, plant viruses produce suppressors of RNA silencing (Viral suppressors of RNA silencing, VSRSs), which are essential for viruses to invade their specific host plants. Interactions of these VSRSs with the hosts' silencing pathways, and their direct and indirect interference with different cellular regulatory networks constitute one of the main lines of the molecular virus-host interactions. Here we have used a microarray approach to study the effects of the Potato virus X Potexvirus (PVX)-specific P25 VSRS protein on the transcript profile of tobacco plants, when expressed as a transgene in these plants.ResultsThe expression of the PVX-specific P25 silencing suppressor in transgenic tobacco plants caused significant up-regulation of 1350 transcripts, but down-regulation of only five transcripts in the leaves, and up- and down-regulation of 51 and 13 transcripts, respectively, in the flowers of these plants, as compared to the wild type control plants. Most of the changes occurred in the transcripts related to biotic and abiotic stresses, transcription regulation, signaling, metabolic pathways and cell wall modifications, and many of them appeared to be induced through up-regulation of the signaling pathways regulated by ethylene, jasmonic acid and salicylic acid. Correlations of these alterations with the protein profile and related biological functions were analyzed. Surprisingly, they did not cause significant alterations in the protein profile, and caused only very mild alteration in the phenotype of the P25-expressing transgenic plants.ConclusionExpression of the PVX-specific P25 VSRS protein causes major alterations in the transcriptome of the leaves of transgenic tobacco plants, but very little of any effects in the young flowers of the same plants. The fairly stable protein profile in the leaves and lack of any major changes in the plant phenotype indicate that the complicated interplay and interactions between different regulatory levels are able to maintain homeostasis in the plants.

Project description:UnlabelledMost plant viruses counter the RNA silencing-based antiviral defense by expressing viral suppressors of RNA silencing (VSRs). In this sense, VSRs may be regarded as virulence effectors that can be recognized by the host as avirulence (avr) factors to induce R-mediated resistance. We made use of Agrobacterium-mediated transient coexpression of VSRs in combination with Potato virus X (PVX) to recapitulate in local tissues the systemic necrosis (SN) caused by PVX-potyvirus synergistic infections in Nicotiana benthamiana. The hypersensitive response (HR)-like response was associated with an enhanced accumulation of PVX subgenomic RNAs. We further show that expression of P25, the VSR of PVX, in the presence of VSR from different viruses elicited an HR-like response in Nicotiana spp. Furthermore, the expression of P25 by a Plum pox virus (PPV) vector was sufficient to induce an increase of PPV pathogenicity that led to necrotic mottling. A frameshift mutation in the P25 open reading frame (ORF) of PVX did not lead to necrosis when coexpressed with VSRs. These findings indicate that P25 is the main PVX determinant involved in eliciting a systemic HR-like response in PVX-associated synergisms. Moreover, we show that silencing of SGT1 and RAR1 attenuated cell death in both PVX-potyvirus synergistic infection and the HR-like response elicited by P25. Our study underscores that P25 variants that have impaired ability to suppress RNA silencing cannot act as elicitors when synergized by the presence of other VSRs. These findings highlight the importance of RNA silencing suppression activity in the HR-like response elicited by VSRs in certain hosts.ImportanceThe work presented here describes how the activity of the PVX suppressor P25 elicits an HR-like response in Nicotiana spp. when overexpressed with other VSR proteins. This finding suggests that the SN response caused by PVX-associated synergisms is a delayed immune response triggered by P25, once it reaches a threshold level by the action of other VSRs. Moreover, this work supports the contention that the silencing suppressor activity of PVX P25 protein is a prerequisite for HR elicitation. We propose that unidentified avr determinants could be involved in other cases of viral synergisms in which heterologous "helper" viruses encoding strong VSRs exacerbate the accumulation of the avr-encoding virus.

Dataset Information

The ability of PVX p25 to form RL structures in plant cells is necessary for its function in movement, but not for its suppression of RNA silencing.

Publications

The ability of PVX p25 to form RL structures in plant cells is necessary for its function in movement, but not for its suppression of RNA silencing.

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