Recombinant Faba bean necrotic yellows virus Putative movement protein (DNA-M)
Description
Introduction to Faba Bean Necrotic Yellows Virus
Faba bean necrotic yellows virus (FBNYV) belongs to the genus Nanovirus within the family Nanoviridae. It is characterized by a multipartite genome consisting of eight circular single-stranded DNA segments, each approximately 1 kb in size and individually packaged in small isometric viral particles. Each segment contains a single open reading frame (ORF) and a noncoding sequence with two conserved regions known as the common region stem-loop (CR-SL) and the major common region (CR-M) . The genome organization follows a one-segment/one-gene pattern, with different segments encoding specific proteins including a cell cycle link protein (Clink), a movement protein (MP), a nuclear shuttle protein (NSP), a master-replication initiator protein (M-Rep), a capsid protein (CP), and three proteins with unknown functions .
FBNYV is a significant pathogen affecting leguminous crops, particularly faba beans (Vicia faba), causing characteristic yellowing symptoms and substantial crop losses. The virus is naturally transmitted by aphid vectors, notably Acyrthosiphon pisum, through a complex process that requires specific helper factors for successful transmission . Interestingly, research has shown that purified FBNYV alone cannot be transmitted by its aphid vector, regardless of the acquisition method, suggesting the requirement of helper factors that may be absent or non-functional in purified virus preparations .
Genomic Context of the Movement Protein
Within the FBNYV genome, the DNA-M segment represents one of the six identified components (designated C1 to C6). Like other segments, DNA-M contains a single major open reading frame in the virion sense, accompanied by a TATA box and polyadenylation signal. The noncoding region contains a highly conserved sequence that potentially forms a stem-loop structure, which is believed to be involved in viral replication and encapsidation processes .
Unlike some other viral proteins such as the replicase-associated protein (Rep) encoded by segments C1 and C2, which share similarities with proteins from related viruses, the movement protein encoded by DNA-M appears to have unique characteristics. While the function of this protein can be inferred from its designation as a movement protein, detailed molecular studies on its specific mechanisms of action remain an area of active research.
Recombinant Production of FBNYV Movement Protein
The recombinant form of the FBNYV putative movement protein is produced using Escherichia coli expression systems, which offer advantages including short culturing time, easy genetic manipulation, and low-cost media . The production process typically involves cloning the DNA-M gene into an expression vector, transforming it into a suitable E. coli strain, inducing protein expression, and subsequently purifying the recombinant protein.
Expression System and Methodology
The commercially available recombinant full-length FBNYV movement protein is expressed in E. coli with an N-terminal histidine tag (His-tag) . The expression likely utilizes the T7 system, which is the most popular approach for producing proteins in E. coli. In this system, an expression vector containing the gene of interest (in this case, the DNA-M gene) is cloned downstream of the T7 promoter and introduced into a T7 expression host. These hosts carry a chromosomal copy of the phage T7 RNA polymerase gene, and when an inducer is added, T7 RNA polymerase is expressed and becomes dedicated to the transcription of the target gene .
The addition of the His-tag to the N-terminus of the protein facilitates purification through affinity chromatography and can aid in protein detection during analytical procedures. After expression, the protein is typically purified to a high degree (greater than 90% as determined by SDS-PAGE) and prepared for distribution in a lyophilized powder form .
Functional Roles in Viral Infection Cycle
The movement protein of FBNYV plays a critical role in the viral infection cycle, primarily facilitating the cell-to-cell movement of the virus within the host plant. This function is essential for establishing a systemic infection, as it allows the virus to spread from the initial infection site to surrounding cells and eventually throughout the plant.
Cell-to-Cell Movement Mechanism
While the exact mechanism of how the FBNYV movement protein facilitates viral movement has not been fully elucidated in the available search results, it likely functions similar to movement proteins of other plant viruses. Generally, viral movement proteins modify the size exclusion limit of plasmodesmata (the cytoplasmic channels connecting adjacent plant cells) to allow the passage of viral nucleic acids or virus particles. The hydrophobic nature of the FBNYV movement protein suggests that it may interact with cellular membranes, potentially facilitating its role in modifying plasmodesmatal structure or function.
Interaction with Alphasatellites
Moreover, the association of SCSA 1 with FBNYV has been shown to increase the rate of plant-to-plant transmission by a process seemingly unrelated to the simple increase of viral accumulation in the vector . This finding indicates a complex interplay between the virus, its genomic components, associated alphasatellites, and the transmission process, with potential implications for the role of the movement protein in these interactions.
Comparative Analysis with Related Viral Proteins
The FBNYV movement protein shares functional similarities with movement proteins from other plant viruses, but its specific sequence and structural characteristics appear to be unique. While the capsid protein of FBNYV shares significant amino acid identity (56.2%) with that of subterranean clover stunt virus (SCSV), and its replicase-associated proteins show close relationships with those of banana bunchy top virus (BBTV), similar direct comparisons for the movement protein are not provided in the available search results .
The component C4 of FBNYV, which appears to be associated with the DNA-M segment encoding the movement protein, potentially codes for a hydrophobic protein that seems structurally and functionally similar to the BBTV-C4 and SCSV-C1 proteins . This suggests some degree of conservation in the function of movement or movement-like proteins across different nanoviruses, despite potential differences in their primary sequences.
FBNYV is clearly distinct from any known virus but is taxonomically related to BBTV and SCSV . This taxonomic relationship may extend to similarities in the function and mechanism of action of their respective movement proteins, although specific comparative studies on these proteins would be needed to establish the extent of these similarities.
Applications and Research Implications
The recombinant FBNYV movement protein serves as a valuable tool for various research applications, particularly in understanding viral pathogenesis, host-virus interactions, and the development of antiviral strategies. By studying the properties and functions of this protein, researchers can gain insights into fundamental aspects of viral biology and potentially develop novel approaches to control viral diseases in crops.
Development of Antiviral Strategies
Understanding the structure and function of the FBNYV movement protein could lead to the development of novel antiviral strategies targeting this essential component of the viral lifecycle. Inhibitors specifically designed to disrupt the function of the movement protein could potentially prevent viral spread within the host plant, limiting infection and reducing crop losses.
Furthermore, knowledge of the protein's role in the complex interactions between the virus, alphasatellites, and aphid vectors could inform integrated pest management strategies aimed at disrupting viral transmission and spread in agricultural settings.
Product Specs
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Target Background
Q&A
What is Faba bean necrotic yellows virus and how is its genome organized?
Faba bean necrotic yellows virus (FBNYV) belongs to the genus Nanovirus in the family Nanoviridae. Its genome consists of eight individually encapsidated circular single-stranded DNA components. FBNYV primarily infects faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) and is frequently found in association with satellite molecules known as alphasatellites. The virus has been identified in multiple countries including Azerbaijan, Egypt, Iran, Morocco, Spain, Syria, and Tunisia, with the DNA-M component showing the highest degree of diversity among the genomic components .
What is the structural composition of the DNA-M component in FBNYV?
The DNA-M component of FBNYV encodes the putative movement protein, which consists of 114 amino acids. The complete amino acid sequence is: MADTGYYAGYQDDVDVDEQKRHQALYLIGIILLVTVCLTVLWVCIMLACYVPGFLKKTLEAWLNSSSLMKRRVASTLTRTPFEATGPERERNWEARRQSTTVNPASQPNTGSVF . This protein is believed to function as a movement protein that facilitates the spread of the virus between plant cells, similar to movement proteins in other plant viruses.
How does FBNYV differ from other nanoviruses in terms of genome structure?
FBNYV possesses a more complex genomic organization compared to many other viruses, with 11 distinct DNA components (C1 to C11) identified in some isolates. Five of these components (C1, C2, C7, C9, and C11) encode different but related replication initiator (Rep) proteins of approximately 33 kDa each. This multi-component genome structure allows for specialized functions across the viral life cycle, with the DNA-M component specifically dedicated to cell-to-cell movement functions .
What expression systems are most effective for producing recombinant FBNYV DNA-M protein?
The bacterial expression system using E. coli has been successfully employed for the production of recombinant FBNYV DNA-M protein. Specifically, full-length DNA-M protein (1-114 amino acids) from the Egyptian isolate (EV1-93) has been expressed with an N-terminal His tag in E. coli . For optimal expression, the protein should be cloned into appropriate expression vectors with strong promoters (like T7) and purified using affinity chromatography methods that leverage the His tag, such as immobilized metal affinity chromatography (IMAC).
What are the optimal storage conditions for recombinant FBNYV DNA-M protein?
Recombinant FBNYV DNA-M protein is typically provided as a lyophilized powder and should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL. To prevent protein degradation, it is recommended to add glycerol to a final concentration of 5-50% (typically 50%) and store working aliquots at 4°C for up to one week. For long-term storage, the protein should be kept at -20°C or -80°C. Repeated freeze-thaw cycles should be avoided as they can lead to protein denaturation and loss of activity .
How can researchers verify the purity and activity of recombinant DNA-M protein?
Purity assessment of recombinant DNA-M protein can be performed using SDS-PAGE, with high-quality preparations typically showing purity greater than 90%. Functional activity can be assessed through membrane binding assays, since the movement protein is expected to associate with cellular membranes, particularly the endoplasmic reticulum. Additionally, researchers can utilize fluorescently tagged versions of the protein to visualize its localization within plant cells and its association with plasmodesmata, which would be consistent with its putative role in cell-to-cell movement .
What experimental approaches can be used to study the membrane-binding properties of DNA-M protein?
To study the membrane-binding properties of DNA-M protein, researchers can employ several approaches:
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Subcellular fractionation: Separate cellular components followed by Western blotting to detect the protein in membrane fractions.
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Confocal microscopy: Express fluorescently tagged DNA-M protein to visualize its localization to membranes.
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Liposome binding assays: Evaluate the protein's affinity for artificial membrane systems of defined composition.
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Membrane yeast two-hybrid systems: Identify potential membrane-associated interaction partners.
These approaches can reveal whether DNA-M, like other viral movement proteins, has reticulon-like properties that allow it to induce membrane curvature, which may be critical for its function in virus movement through plasmodesmata .
How does the FBNYV DNA-M protein facilitate cell-to-cell movement of the virus?
Based on studies of similar viral movement proteins, FBNYV DNA-M likely facilitates cell-to-cell movement through plasmodesmata (PD) by:
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Modifying PD structure to increase size exclusion limit
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Utilizing cellular endomembranes, particularly the endoplasmic reticulum (ER)
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Potentially inducing constrictions in ER tubules similar to reticulon proteins
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Forming PD-anchored virus replication compartments
The molecular mechanisms may involve the protein's W-like topology within the ER membrane and its ability to induce membrane curvature. These properties could contribute to the formation of viral movement complexes that transport viral genomic components through the plasmodesmata .
What is known about the interaction between DNA-M and other FBNYV genomic components?
Studies on FBNYV genomic components reveal a complex interplay between different viral proteins. While DNA-M encodes the putative movement protein, the replication of this component (along with other non-Rep encoding components) depends on the activity of Rep proteins, particularly Rep2. This "master replication protein" is capable of initiating replication of all other genome components in trans. This relationship suggests a coordinated expression system where Rep2 plays a central role in viral genome replication, while DNA-M facilitates the intercellular movement of replicated viral components .
The relationship between DNA-M and other components can be summarized in the following table:
| Component | Primary Function | Relationship with DNA-M |
|---|---|---|
| DNA-M | Cell-to-cell movement | Encodes the putative movement protein |
| C1 (Rep1) | Self-replication | Cannot initiate DNA-M replication in trans |
| C2 (Rep2) | Master replication | Can initiate DNA-M replication in trans |
| C7, C9, C11 | Alternative replication | Cannot efficiently initiate DNA-M replication |
What methodologies are most effective for studying FBNYV transmission by aphid vectors?
Research on FBNYV transmission by aphid vectors can be conducted using several methodologies:
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Controlled acquisition and inoculation feeding experiments: Allow aphids to feed on infected plants for specific acquisition access periods (AAP) followed by inoculation access periods (IAP) on healthy plants.
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PCR-based detection in aphids: Use primers targeting the virus replicase gene (290 bp fragment) to detect FBNYV in viruliferous aphids.
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Transmission efficiency experiments: Compare transmission rates across different aphid species and developmental stages.
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Temporal dynamics studies: Examine the latent period in the aphid (approximately 18 hours) and retention period (up to 18 days).
Research has shown that FBNYV is transmitted most efficiently by Aphis craccivora (93.84% transmission), followed by A. fabae (89.09%), A. pisum (77.50%), A. sesbaniea (56.25%), and A. gossypii (38.46%) .
How does FBNYV acquisition and transmission vary among different aphid species and developmental stages?
FBNYV transmission studies reveal significant variations in transmission efficiency:
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Species variation: Five aphid species can transmit FBNYV with different efficiency rates: A. craccivora > A. fabae > A. pisum > A. sesbaniea > A. gossypii.
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Developmental stage impact: Nymphal stages transmit FBNYV more efficiently than adult stages (78.7% vs. 34.3%, respectively).
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Acquisition parameters: The optimal acquisition access period (AAP) is 2 hours, while the inoculation access period (IAP) can be as short as 0.5 hours.
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Temporal factors: FBNYV can be acquired by A. craccivora after a 4-day post-inoculation period in plants. The virus has a latent period of approximately 18 hours in the aphid and can be retained for up to 18 days.
It's important to note that FBNYV is not transmitted transovarially through new progenies of A. craccivora, and newly hatched nymphs without prior virus acquisition cannot transmit the virus .
How does FBNYV DNA-M protein compare structurally and functionally to movement proteins of other plant viruses?
FBNYV DNA-M protein belongs to a distinct class of viral movement proteins (MPs) with some features that may be similar to those found in other plant viruses:
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Membrane association: Like MPs from other viruses such as Hibiscus green spot virus (HGSV), FBNYV DNA-M protein likely associates with the endoplasmic reticulum (ER).
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Plasmodesmatal targeting: The protein likely targets plasmodesmata (PD) and increases their size exclusion limit, enabling virus movement.
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Reticulon-like properties: Some viral MPs, like those in HGSV and Potato virus X (PVX), induce constrictions of ER tubules and exhibit an affinity for highly curved membranes, properties that may be shared by FBNYV DNA-M.
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Topology: The DNA-M protein may adopt specific membrane topologies that facilitate its function, potentially similar to the W-like topology observed in some reticulon-like viral MPs .
What advanced techniques can be employed to study the interaction between FBNYV DNA-M and host cellular components?
Several advanced techniques can be employed to study DNA-M interactions with host components:
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Bimolecular Fluorescence Complementation (BiFC): To visualize protein-protein interactions in living cells.
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Proximity Ligation Assay (PLA): For detecting protein interactions with high sensitivity and specificity.
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Co-immunoprecipitation coupled with mass spectrometry: To identify host proteins interacting with DNA-M.
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Cryo-electron microscopy: To visualize the structure of DNA-M and its complexes at near-atomic resolution.
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CRISPR-Cas9 gene editing: To manipulate host factors potentially involved in DNA-M function.
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Live-cell imaging with super-resolution microscopy: To track DNA-M movement and localization in real-time.
These techniques would provide insights into how DNA-M interacts with host endomembranes, plasmodesmata components, and the cytoskeleton, which are likely crucial for its function in facilitating viral movement .
What are the evolutionary relationships between FBNYV DNA-M and movement proteins from other nanoviruses?
Evolutionary analysis of FBNYV DNA-M shows that it shares sequence similarity with movement proteins from other nanoviruses, but with notable diversity. Genome sequences of FBNYV isolates from different countries (Azerbaijan, Egypt, Iran, Morocco, Spain, Syria, and Tunisia) have shown that the DNA-M component displays the highest degree of diversity among all viral components, with sequence identity greater than 84% between isolates .
This diversity may reflect adaptations to different host species or vectors in various geographical regions. Comparative genomic analysis across the Nanoviridae family could reveal conserved functional domains essential for movement protein activity and identify regions under positive selection pressure that might be involved in host-specific adaptations or immune evasion strategies.
