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Potato virus X (PVX) requires three virally encoded proteins, the triple gene block (TGB), for movement between cells. TGB1 is a multifunctional protein that suppresses host gene silencing and moves from cell to cell through plasmodesmata, while TGB2 and TGB3 are membrane-spanning proteins associated with endoplasmic reticulum-derived granular vesicles. Here, we show that TGB1 organizes the PVX \"X-body,\" a virally induced inclusion structure, by remodeling host actin and endomembranes (endoplasmic reticulum and Golgi). Within the X-body, TGB1 forms helically arranged aggregates surrounded by a reservoir of the recruited host endomembranes. The TGB2/3 proteins reside in granular vesicles within this reservoir, in the same region as nonencapsidated viral RNA, while encapsidated virions accumulate at the outer (cytoplasmic) face of the X-body, which comprises a highly organized virus \"factory.\" TGB1 is both necessary and sufficient to remodel host actin and endomembranes and to recruit TGB2/3 to the X-body, thus emerging as the central orchestrator of the X-body. Our results indicate that the actin/endomembrane-reorganizing properties of TGB1 function to compartmentalize the viral gene products of PVX infection.

Here, we report the detection and complete genome sequence of a novel potexvirus, tentatively named “Adenium obesum virus X” (AobVX), isolated from Adenium obesum, that was sent for virus screening at Australian Government post-entry quarantine (PEQ) facilities after being imported into Australia from China. The AobVX genome is 6781 nucleotides in length excluding the poly(A) tail and is predicted to encode conserved potexvirus proteins and sequence motifs across five open reading frames. The RNA-dependent RNA polymerase of this virus shares the highest amino acid sequence similarity with that of nerine potexvirus 1 (58.7% identity) and nerine virus X (58.58% identity). This is the first report of a positive-sense single-stranded RNA virus in A. obesum related to members of the genus Potexvirus in the family Alphaflexiviridae.

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.

Taxonomy Potato virus X is the type‐member of the plant‐infecting Potexvirus genus in the family Alphaflexiviridae. Physical properties Potato virus X (PVX) virions are flexuous filaments 460–480 nm in length. Virions are 13 nm in diameter and have a helical pitch of 3.4 nm. The genome is approximately 6.4 kb with a 5′ cap and 3′ poly(A) terminus. PVX contains five open reading frames, four of which are essential for cell‐to‐cell and systemic movement. One protein encodes the viral replicase. Cellular inclusions, known as X‐bodies, occur near the nucleus of virus‐infected cells. Hosts The primary host is potato, but it infects a wide range of dicots. Diagnostic hosts include Datura stramonium and Nicotiana tabacum. PVX is transmitted in nature by mechanical contact. Useful website https://talk.ictvonline.org/ictv‐reports/ictv_online_report/positive‐sense‐rna‐viruses/w/alphaflexiviridae/1330/genus‐potexvirus Potato virus X, one of the oldest known and well‐studied plant viruses, has contributed much to our current knowledge of plant immunity in potato and tobacco, and is a versatile vector for expressing foreign genes in plants.

Strawberry mild yellow edge virus (SMYEV) is a member of the genus Potexvirus, family Alphaflexiviridae. It is one of the most common pathogenic viruses infecting cultivated strawberries worldwide. In this study, we investigated the genetic diversity of SMYEV in strawberry fields that were severely affected by strawberry decline disease in the eastern Canadian provinces of New Brunswick, Nova Scotia, Prince Edward Island and Quebec. A total of 134 SMYEV coat protein (CP) gene sequences, representing 85 nucleic acid haplotypes, were identified in 56 field samples. A highly divergent SMYEV population was found in all four provinces, but there was little genetic differentiation among the populations, and moreover, the Canadian SMYEV isolates formed a unique dissimilar, genetically divergent population group when compared to those reported in other countries. Phylogenetic analysis revealed three new SMYEV subclades that consisted mainly of Canadian variants and were composed of 76 sequence haplotypes (76/85, 88%). Mixed infections by different SMYEV variants were observed in 38 samples (38/56, 68%). Evolutionary analysis suggested that the SMYEV strains in eastern Canada possibly originated outside of Canada but adapted to conditions in the region through genetic mutations.

Potato aucuba mosaic virus (PAMV), a positive single-strand RNA virus, has one of the longest genomes of the viruses in the genus Potexvirus. In 2019, potato samples with mottle and crinkling symptoms from Huzhou, Zhejiang province, China, were identified to be infected with PAMV, potato virus X (PVX), and potato virus Y (PVY) by transcriptome sequencing. To study the effects of single infection by PAMV, the full-length sequence of PAMV from Huzhou (MT193476) was determined and an infectious full-length cDNA clone was constructed. This cDNA clone was infectious by agro-infiltration, leading to systemic symptoms in Nicotiana benthamiana, tomato, pepper, and potato.

ABSTRACT The transcription factor NbTFIISL, a TFIIS‐like protein in Nicotiana benthamiana, plays a critical role in facilitating bamboo mosaic virus (BaMV) infection. BaMV infections significantly downregulate NbTFIISL expression, with transcript levels reduced to 38% by 7 days post‐inoculation. Virus‐induced gene silencing of NbTFIISL impaired BaMV accumulation, reducing coat protein levels to ~45% and leading to smaller GFP‐labelled infection foci. Protoplast‐based assays further confirmed its involvement in viral replication, with BaMV RNA levels dropping to 12% in NbTFIISL‐silenced cells. Subcellular localisation analysis revealed that NbTFIISL is primarily nuclear, directed by a classical nuclear localisation signal (NLS) and an LW motif. Mutant constructs lacking these signals—NbTFIISL/ΔNLS and NbTFIISL/ΔNLS/ΔLW—lost nuclear targeting and instead localised to mitochondria, with the double mutant forming distinct speckle‐like aggregates. Overexpression experiments uncovered a dual role for NbTFIISL: nuclear‐localised wild‐type protein induced necrosis, whereas mitochondria‐localised NbTFIISL/ΔNLS significantly enhanced BaMV accumulation (~148%). In contrast, protein aggregation in the NbTFIISL/ΔNLS/ΔLW mutant partially impaired this enhancement. Yeast two‐hybrid assays revealed specific interactions between NbTFIISL and BaMV proteins, including the replicase RdRp domain and movement protein TGBp1. These findings suggest that NbTFIISL promotes BaMV replication through mitochondrial relocalisation and interaction with viral proteins, whereas its nuclear presence may trigger necrosis, potentially limiting viral spread. This study highlights the multifunctional roles of NbTFIISL and advances our understanding of host factors in plant–virus interactions and viral pathogenesis. BaMV infection induces dynamic relocalisation of NbTFIISL and its mutants to mitochondria in Nicotiana benthamiana, as revealed by subcellular colocalisation analysis.

Potato virus X (PVX) belongs to genus Potexvirus. This study characterizes the cellular transcriptome responses to PVX infection in Russet potato at 2 and 3 days post infection (dpi). Among the 1242 differentially expressed genes (DEGs), 268 genes were upregulated, and 37 genes were downregulated at 2 dpi while 677 genes were upregulated, and 265 genes were downregulated at 3 dpi. DEGs related to signal transduction, stress response, and redox processes. Key stress related transcription factors were identified. Twenty-five pathogen resistance gene analogs linked to effector triggered immunity or pathogen-associated molecular pattern (PAMP)-triggered immunity were identified. Comparative analysis with Arabidopsis unfolded protein response (UPR) induced DEGs revealed genes associated with UPR and plasmodesmata transport that are likely needed to establish infection. In conclusion, this study provides an insight on major transcriptional regulatory networked involved in early response to PVX infection and establishment.

ABSTRACT Counteracting plant RNA silencing ensures successful viral infection. The P25 protein encoded by potato virus X (PVX) is a multifunctional protein that acts as a viral RNA silencing suppressor (VSR). In this study, we screened out a potato type I protease inhibitor (PI) in Nicotiana benthamiana (NbPI) that interacts with P25. Silencing of NbPI by tobacco rattle virus (TRV)‐mediated virus‐induced gene silencing (VIGS) promoted the infection of PVX. Overexpression of NbPI in transgenic plants conferred resistance to PVX infection. Moreover, transient expression of NbPI impaired the VSR activity and cell‐to‐cell movement complementation ability of P25. Further experiments showed that P25 protein degradation was through the combination of autophagy and the ubiquitin‐26S proteasome system (UPS), leading to impairment of P25. Taken together, we have identified NbPI as a new host factor that compromises PVX infection by targeting and degrading the VSR P25. A new host factor potato type I protease inhibitor in Nicotiana benthamiana (NbPI) targets and degrades P25 of potato virus X (PVX), leading to impaired viral RNA silencing suppressor function and reduced PVX infectivity.

The genomes of two novel viruses were assembled from 454 pyrosequencing data obtained from vanilla leaves from La Réunion. Based on genome organization and homologies, one agent was unambiguously classified as a member of the genus Potexvirus and named vanilla virus X (VVX). The second one, vanilla latent virus (VLV), is phylogenetically close to three unclassified members of the family Alphaflexiviridae with similarity to allexiviruses, and despite the presence of an additional 8-kDa open reading frame, we propose to include VLV as a new member of the genus Allexivirus . Both VVX and VLV were mechanically transmitted to vanilla plants, resulting in asymptomatic infections.