Citrus Virology- Introduction · Citrus Virology- Introduction. Amit Levy. [email protected] 863-956-8704. What is a Virus? • Viruses are very small particles that can infect animals

Citrus Virology- Introduction

Amit [email protected]

863-956-8704

mailto:[email protected]

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.

Outline:

• How are viruses packed?

• How do viruses multiply?

• How do viruses spread?

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

http://viralzone.expasy.org/by_protein/245




Outline:







8.7 kb960 nm long

helical




3.64 kb38 nm length

capsid



nucleocapsids


19.3 kb2000 nm long

helical



8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length





How are viruses packed? Virion

• Virion is the infectious particle

• composed of :• nucleic acid • protein capsid • (+/- envelope)

Icosahedral Helical

Viral Capsids

Wendell M. Stanley1946 Nobel Prize in ChemistryCrystallized Tobacco Mosaic Virus andInvestigated its Biochemistry

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’

Icosahedral- triangular structures laid side by side

T=triangulation number

Icosahedral Helical

Epcot center

Outline:




How do viruses replicate?

DNA OR RNA Shape

Circular Linear

Number One Or more

Strands ss ds + or - if RNA

Virus genome can be:




8.7 kb960 nm long

helical




3.64 kb38 nm length

capsid



nucleocapsids


19.3 kb2000 nm long

helical



8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length






Replicase: RNA Dependent RNA Polymerase

MP- Movement ProteinCP- coat protein

+ strand RNA virus

+ 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

Citrus Psorosis virus:(-) sense RNA virus

(-) sense genome)

Transcription by RDRP

+ sense genome

Protein Products

(-) sense genome)

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

2. Replication


Cellular DNA replication protein Double

stranded DNA genome

Cellular DNA replication proteins


Citrus chlorotic dwarfssDNA virus

Outline:




TMV-GFP

1.Inoculated leaf- local lesions

2.Systemic movement to sink leaves in phloem

Tobacco Mosaic Virus

Size of plasmodesmata ~50 nmWith available space ~5-10 nmCTV is 2000 nm!

Viruses use Movement Proteins to move

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

PD (PDLP1-GFP) 30 K RFP5 3RdRP

MT/HEL

Merge

cell1

cell2

Hipper et al. 2013

2. Systemic movement(Red arrows in the figure)

• 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




8.7 kb960 nm long

helical




3.64 kb38 nm length

capsid



nucleocapsids


19.3 kb2000 nm long

helical



8.7, 5 kb8.4, 3.2, 3.1 kb150 nm length





Agueroet al. 2013


Can be transferred mechanically between plants

1. Local AND systemic movement

2. Local movement Only

Citrus leprosis-

Transmitted between plants by insects feeding on leaf cells

PDS silencing,Hajeri et al. 2014

Transmitted by phloem sucking insects

3. Systemic movement only-

Citrus tristeza virus-

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

Replication: PospiviroidaeUse HOST proteins

RNA dependent RNA polymerase RNA cleavage RNA ligase

Ding et al. 1999

Documents

Citrus Virology- Introduction · Citrus Virology- Introduction. Amit Levy. [email protected] 863-956-8704. What is a Virus? • Viruses are very small particles that can infect animals