Plant Virus Transmission Mechanisms

Plant Virus Transmission Mechanisms

• Plant viruses can be transmitted through various methods, including mechanical, seed, pollen, vegetative propagation, grafting, and dodder.

Mechanical Transmission

• This method involves physical contact between infected and healthy plants.
• Viruses can spread through contaminated tools, vectors, or plant fluids.
• This is a common way for many viruses to spread, but it's not the most efficient.

Seed Transmission

• Some viruses can infect developing embryos by direct invasion after fertilization or indirect invasion by infecting the gametes before fertilization.
• The percentage of seed transmission depends on the virus, the host plant, the time of infection of the mother plant, and the seed's age.
• The distribution of virus-infected seeds in infected mother plants is random.

Pollen Transmission

• Viruses can be transmitted through pollen from infected plants to healthy ones; in this manner, viruses can spread quickly and widely.

Vegetative Propagation

• Transmission occurs through growing processes such as stem cuttings, root grafts, or other plant propagation methods.
• This is a common method for certain virus types to spread and infect numerous plants.

Grafting

• Viruses can be transmitted when propagating by grafting plants.
• The virus spreads rapidly and widely through the grafting process.

Dodder

• A parasitic plant (dodder) can transmit viruses through its parasitic relationships.

Transmission by Invertebrates

• Arthropoda (Insects):
  • Insecta (e.g., aphids, leafhoppers, planthoppers, cicadas) are the most common insect vectors.
  • Arachnida (e.g., spider mites, and eriophyid mites) are also commonly involved.
• Nematodes:
  • Nematodes can also transmit some plant viruses.

Viral Genome Organization and Strategies

• A. General Properties of Plant Viral Genomes: Plant viruses may have single or multiple genomic RNA/DNA pieces.
  • Kind of NA: The type of nucleic acid (RNA or DNA) in the virus.
  • Number of genome pieces (components): The number of distinct RNA/DNA segments in the virus.
  • Terminal structures: Often have specific sequences at the ends of their RNA or DNA.
  • nt sequence: Specific order of nucleotides.
  • Regulatory signals: Sequences that regulate viral gene expression.
  • mRNAs: The messenger RNA molecules produced during viral transcription.
• B. Coding regions: Areas of the genome containing genes for viral proteins.
  • initiation codon: (AUG, AUU, CUG) Start codon for protein synthesis.
  • stop codon: (UAA, UAG, UGA) Stop codon for protein synthesis.
• C. Non-coding regions: Areas in the genome that do not encode proteins; these regions may have important roles, such as regulatory sequences.
  • End-group structures: Structures at the ends of the RNA/DNA molecule.
  • 3′ and 5′ non-coding regions (NCR): Non-coding regions located on the 3' and 5' ends of the genome.
  • Intergenic regions: Non-coding regions between genes.
• 1. Subgenomic RNAs: Some viruses generate smaller RNA molecules from one larger genome RNA molecule. These are used to make sub-genomic mRNAs.
• 2. Polyprotein strategy: Some viruses make long proteins (polyproteins) that are then cut into smaller, functional proteins.
• 3. Multi-partite genomes: Some viruses have multiple RNA or DNA molecules (segments). All these segments are packaged in the same virion.
• 4. Internal initiation: Some viruses can initiate translation at internal ribosome entry sites (IRES) instead of the normal 5' cap-dependent method.
• 5. Leaky scanning: This approach allows the ribosome to continue translating into a new open reading frame (ORF) upon encountering a stop codon in one ORF.
• 6. Read-through: Ribosomes sometimes ignore a stop codon and continue translating into another ORF.
• 7. Frame-shift: A change in the reading frame during translation.
• 8. Splicing: A process where non-coding regions are removed from a viral mRNA molecule before it's translated into protein.

Viral Protein Functions

• Viral proteins can be structural (forming parts of the virus particle) or functional (enzymes involved in various viral processes, such as replication or movement). They can also play other specific tasks such as interacting with host cells and/or the host's immune systems.

Virus Replication

• Replicative intermediate (RF): Intermediate stage in replication.
• Semiconservative replication: Each new DNA molecule contains one original strand and one new strand.
• Conservative replication: Each new DNA molecule consists of two new strands formed from an original.

Transmission characteristics

• Site of transmission: The place where transmission happens (e.g., foregut, midgut, etc.).
• Type of transmission: How the virus is transmitted between plants or vectors.
• Virus product interacting with vector: This refers to specific factors.
• Acquisition time: Estimated time the vector takes to acquire the virus.
• Retention time: How long the vector retains the virus.
• Viruses in vector hemolymph: The presence of virus in the insect's hemolymph.
• Latent period: Time between acquisition and symptom expression.
• Transovarial transmission: Transmission of the virus from an infected mother to her offspring .
• Transmission characteristics: The way in which the virus spreads.

Additional Notes

• Plant viruses use various mechanisms to move systemically and infect the plant’s cells.
• Many plant viruses rely on invertebrate vectors that carry viruses between infected plants and healthy ones.

Explore the various methods of plant virus transmission, including mechanical, seed, pollen, and other propagation techniques. Understand the efficiency and processes involved in each transmission mechanism in this informative quiz. Test your knowledge on how plant viruses spread and affect agriculture.