citrus virology- introduction · citrus virology- introduction. amit levy. [email protected]...
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What is a Virus?• Viruses are very small particles that can infect
animals and plants and sometimes make them sick.
• Viruses are made up of genetic materials like DNA or RNA and are protected by a coating of protein (CP).
• Are all sub-microscopic
• Viruses hijack the cells of living organisms. They then use the cell to replicate and take over more cells. Only reproduce in living organisms.
• Are viruses alive?Most scientists will say they are non-living because they cannot reproduce without the aid of a host. Viruses also do not metabolize food into energy or have organized cells, which are usually characteristics of living things. Also do not divide like bacteria.
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Outline:
• How are viruses packed?
• How do viruses multiply?
• How do viruses spread?
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Name Genus Genome Size particle
Citrus leaf blotch virus
Citrivirus Linear ssRNA(+) genome
8.7 kb960 nm long
helical
Citrus chlorotic dwarf
Geminiviridae(family)
circular, ssDNA genome
3.64 kb38 nm length
capsid
Citrus psorosis virus Ophiovirus Segmented negative-stranded RNA
RNA1- 7.8kbRNA2- 1.7kbRNA3- 1.5kbRNA4- 1.4kb
nucleocapsids
Citrus tristeza virus Closterovirus Linear ssRNA(+) genome
19.3 kb2000 nm long
helical
Citrus leprosis Cilevirus / Higrevirus
Bipartite/ tripartite ssRNA(+) genome
8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length
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Outline:
• How are viruses packed?
• How do viruses multiply?
• How do viruses spread?
![Page 6: Citrus Virology- Introduction · Citrus Virology- Introduction. Amit Levy. amitlevy@ufl.edu 863-956-8704. What is a Virus? • Viruses are very small particles that can infect animals](https://reader030.vdocuments.site/reader030/viewer/2022041009/5eb6a68d2ba4201c7124111f/html5/thumbnails/6.jpg)
Name Genus Genome Size particle
Citrus leaf blotch virus
Citrivirus Linear ssRNA(+) genome
8.7 kb960 nm long
helical
Citrus chlorotic dwarf
Geminiviridae(family)
circular, ssDNA genome
3.64 kb38 nm length
capsid
Citrus psorosis virus Ophiovirus Segmented negative-stranded RNA
RNA1- 7.8kbRNA2- 1.7kbRNA3- 1.5kbRNA4- 1.4kb
nucleocapsids
Citrus tristeza virus Closterovirus Linear ssRNA(+) genome
19.3 kb2000 nm long
helical
Citrus leprosis Cilevirus / Higrevirus
Bipartite/ tripartite ssRNA(+) genome
8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length
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How are viruses packed? Virion
• Virion is the infectious particle
• composed of :• nucleic acid • protein capsid • (+/- envelope)
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Icosahedral Helical
Viral Capsids
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Wendell M. Stanley1946 Nobel Prize in ChemistryCrystallized Tobacco Mosaic Virus andInvestigated its Biochemistry
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Tobacco mosaic virus is a ssRNA virus composed of 6000 nucleotides. The capsid is made of 2100 copies of a single protein subunit that contain 158 amino acids.
Helical- protein forming a ‘tube shape’
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Icosahedral- triangular structures laid side by side
T=triangulation number
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Icosahedral Helical
Epcot center
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Outline:
• How are viruses packed?
• How do viruses multiply?
• How do viruses spread?
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How do viruses replicate?
DNA OR RNA Shape
Circular Linear
Number One Or more
Strands ss ds + or - if RNA
Virus genome can be:
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Name Genus Genome Size particle
Citrus leaf blotch virus
Citrivirus Linear ssRNA(+) genome
8.7 kb960 nm long
helical
Citrus chlorotic dwarf
Geminiviridae(family)
circular, ssDNA genome
3.64 kb38 nm length
capsid
Citrus psorosis virus Ophiovirus Segmented negative-stranded RNA
RNA1- 7.8kbRNA2- 1.7kbRNA3- 1.5kbRNA4- 1.4kb
nucleocapsids
Citrus tristeza virus Closterovirus Linear ssRNA(+) genome
19.3 kb2000 nm long
helical
Citrus leprosis Cilevirus / Higrevirus
Bipartite/ tripartite ssRNA(+) genome
8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length
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Citrus leaf blotch virus
Replicase: RNA Dependent RNA Polymerase
MP- Movement ProteinCP- coat protein
+ strand RNA virus
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+ sense genome Translation by cellular ribosomes
Protein production (RDRP- RNA dependent RNA polymerase replicase)
Transcription by RDRP
(-) sense genome)Internal promoters sgRNAs
Translation by cellular ribosomes
Proteins: structural-Movement Protein, Coat protein- assembly and exit
Replication by RDRP
Citrus leaf blotch virus+ strand RNA virus
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Citrus Psorosis virus:(-) sense RNA virus
(-) sense genome)
Transcription by RDRP
+ sense genome
Protein Products
(-) sense genome)
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Citrus chlorotic dwarfssDNA virus
1. Synthesize proteins:
Single strand DNA genome
Cellular DNA replication protein Double
stranded DNA genome
Transcription by host cell RNA polymerase
mRNA
Proteins
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2. Replication
Single strand DNA genome
Cellular DNA replication protein Double
stranded DNA genome
Cellular DNA replication proteins
Single strand DNA genome
Citrus chlorotic dwarfssDNA virus
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Outline:
• How are viruses packed?
• How do viruses multiply?
• How do viruses spread?
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TMV-GFP
1.Inoculated leaf- local lesions
2.Systemic movement to sink leaves in phloem
Tobacco Mosaic Virus
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Size of plasmodesmata ~50 nmWith available space ~5-10 nmCTV is 2000 nm!
Viruses use Movement Proteins to move
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Movement Proteins:
• Alter the formation or function of PD• Increase the available space inside PD
• Coordinating replication of viral gnome with transport to and across wall
• Associate with membranes• Function is highly regulated
MP:GFP in PD
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PD (PDLP1-GFP) 30 K RFP5 3RdRP
MT/HEL
Merge
cell1
cell2
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Hipper et al. 2013
2. Systemic movement(Red arrows in the figure)
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• Plant viruses spread directly cell-to-cell within a leaf without an extracellular phase (local movement)
• For systemic long distance infection an extracellular form is transported leaf- to-leaf through the phloem
• For most plant viruses the extracellular form is the virus particles
• Some viruses move only systemically (no local movement) and some will move only locally (no systemic movement)
• Plant-to-plant movement it tied to systemic movement strategy
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Name Genus Genome Size particle
Citrus leaf blotch virus
Citrivirus Linear ssRNA(+) genome
8.7 kb960 nm long
helical
Citrus chlorotic dwarf
Geminiviridae(family)
circular, ssDNA genome
3.64 kb38 nm length
capsid
Citrus psorosis virus Ophiovirus Segmented negative-stranded RNA
RNA1- 7.8kbRNA2- 1.7kbRNA3- 1.5kbRNA4- 1.4kb
nucleocapsids
Citrus tristeza virus Closterovirus Linear ssRNA(+) genome
19.3 kb2000 nm long
helical
Citrus leprosis Cilevirus / Higrevirus
Bipartite/ tripartite ssRNA(+) genome
8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length
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Agueroet al. 2013
Citrus leaf blotch virus
Can be transferred mechanically between plants
1. Local AND systemic movement
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2. Local movement Only
Citrus leprosis-
Transmitted between plants by insects feeding on leaf cells
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PDS silencing,Hajeri et al. 2014
Transmitted by phloem sucking insects
3. Systemic movement only-
Citrus tristeza virus-
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Viroids:
Viroids are “sub-viruses” composed exclusively of a single circular strand of nucleic acid (RNA)
No coding capacity -do not program their own polymerase, no coat protein
Use host-encoded polymerase for replication.
potato spindle tuber viroid (Pospiviroidae)-rod like structurre
peach latent mosaic viroid (Avsunviroidae)- complex structure
Citrus viroids
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Replication: PospiviroidaeUse HOST proteins
RNA dependent RNA polymerase RNA cleavage RNA ligase
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Ding et al. 1999