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General Virology- Exam 3 > Viruses that Infect Plants > Flashcards

Viruses that Infect Plants Flashcards

1
Q

How are viruses tools for Exploring Basic Cellular Processes?

A

simple systems to manipulate and investigate the functions of cells.

provide valuable information about many aspects of cell biology: (Ex. Source of promoters, delivery systems for gene expression, have simplified the study of genetics)

Increased understanding of the basic mechanisms of molecular genetics (DNA replication, transcription, RNA processing), translation (genetics), protein transport, gene silencing, and immunology.

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2
Q

TMV vector

A

no known vector

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3
Q

Viruses are being used as plant expression vectors for the synthesis of proteins and peptides of commercial interest

A

ex: TMV

Coat protein
Once the capsid protein is expressed- tobacco mosaic virus

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4
Q

Viruses are being used as models and delivery systems for nanotechnology

A

modified TMV

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5
Q

plant viruses are important pathogens because…

A

They cause economic losses in food and fiber production. World-wide losses estimated to be $66 Billion.
Not always readily recognized, identified, distinguished or managed.

Approximately 1/4 of all known virus species (~1100) infect plants

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6
Q

Types of Direct Loses due to Plant Viruses

A

Reduction in growth
Reduction in Vigor
Reduction in Quality or Market Value

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7
Q

Reduction in Growth

A 
yield reduction (including symptomless infection)
crop failure
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8
Q

Reduction in Vigor

A

increased sensitivity to frost & drought

increased predisposition of pathogens and pests

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9
Q

Reduction in Quality or Market Value

A

defects of visual attraction: size, shape, color
reduced keeping quality
reduced consumer appeal: grade, taste, texture,
reduced fitness for propagation

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10
Q

Initiation of Infection

A

Plant viruses lack an active mechanism for cell entry= passive entry

Host receptors are not known for plant viruses.
(NO entry via receptor-mediated endocytosis)

Virus must enter via a wound in the plant cell wall and must be at the site during injury.

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11
Q

Cell Walls

A

Polysaccharides and structural proteins make up the cell walls; waxy layer & pectin; cellulose
No receptor

no virus has evolved a mechanism to directly penetrate the plant cell wall and enter a plant cell

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12
Q

Plasmodesma

A

mechanism to get from cell to cell

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13
Q

Plant Virus Transmission from Plant to Plant (Nature)

A

Contact
Seed
Pollen
Vectors

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14
Q

Plant Virus Transmission from Plant to Plant (Experimental)

A

Contact
Vectors
Particle bombardment (cloned DNA)
Agrobacterium (cloned DNA)

ex: sap

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15
Q

Contact

A

a purely mechanical injury that breaches the cell wall and transiently breaches the plasma membrane of underlying cells

ex: Field/Greenhouse:
Tools, Equipment,
Hands, Water, Soil

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16
Q

Transmission

A
  1. contact
  2. gross injury caused by the mouthparts of a herbivorous arthropods, such as thrips, beetles, mites
  3. injection directly into cells through the piercing mouthparts of sap-sucking arthropods or nematodes (whitefly, aphids, nematodes, leafhopper)
  4. Carriage into plant tissue on or in association with fungal or plant parasites
  5. Grafting of infected tissue onto healthy tissue.
  6. Vegetative propagation
  7. Vertical transmission via seed
  8. Vertical transmission via pollen
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17
Q

Arthropod virus vectors

A

carry virus from diseased to healthy plants
very efficient methods of transmission and movement
viruses and arthropods have very specific relationships

whiteflies, aphids, thrips, leafhopper, mites, beetles

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18
Q

Types of Insect Transmission

A

Non Persistent Transmission (viruses become attached to the distal tip of the stylet of the insect and on the next plant it feeds on, it inoculates it with the virus)

Persistent Transmission

Propagative Transmission (replicate in both the plant and the insect)

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19
Q

Plant Responses to Virus Infection

A 
latent infections- no obvious symptoms
systemic symptoms (macroscopic)
localized symptoms (macroscopic)
microscopic symptoms (cytological changes)
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20
Q

Cytological Changes (microscopic symptoms)

A

Symptoms are caused by deregulation of normal cellular physiology – interference with expression developmental host genes, movement of metabolites, etc.

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21
Q

Abnormal Growth And Developmental- Malformations

A

stunting, twisting of the growing tips, Leaf curling, Leaf distortion

  • Epinasty (unequal growth of two surfaces leading to curling of the whole leaf)
  • Enations (outgrowths from upper or lower surfaces of leaves)
  • Delayed senescence (plants remain vegetative)
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22
Q

Potyvirus

A

genus of viruses in the family Potyviridae
host= Plants
vector= aphids
linear, ssRNA(+) genome
currently 158 species in this genus including the type species Potato virus Y

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23
Q

Systemic Symptoms (growth & developmental abnormalities)

A 
Mosaics
necrosis
chlorsis/yellowing (color changes in the plant)
variegation
ring spots
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24
Q

Mosaics

A

pattern of light and dark areas in dicots, streaks or stripes in
monocots. Due to breakdown of chlorophyll in yellow (light) areas.
Virus Infection may also interfere with normal chloroplast development

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25
Necrosis
apoptotic response | death of tissues, organs or whole plants. Disruption of starch translocation.
26
Chlorsis/yellowing
color changes in plant | clearing or yellowing of the veins and general yellowing of all tissues
27
Variegation
breaking in the color of petals The color breaking consists flecks, streaks, or sectors of tissue with a color different from normal Breaking of petal color, the result of anthocyanin pigment loss, revealing the underlying coloration due to plastid pigments.
28
localized symptoms
“Local lesion” or “hypersensitive” response is an apoptotic response
29
Microscopic Symptoms
light microscopy with selective protein and nucleic acid stains
30
Geminivirus
ssDNA plant virus
31
Plant Virus Classification
virion morphology genomic organization biology - vector transmission, host range (Characteristic symptoms & Common name of host species)
32
Virion morphology
Rod/filamentous shaped viruses Isometric viruses Bacilliform morphology Geminate- fusion of two incomplete icosahedra (unique to plant viruses)
33
Genome Structure
Plant viral genomes very small in comparison to genomes of other viruses - only about 2,700 – 26,000 nucleotides Genomes can be RNA or DNA
34
Viral genomes of RNA plant viruses
most are: single-stranded, linear, messenger sense RNA genome
35
Monopartite viruses
carry genomic information in a single virus particle | ex: Tobamoviruses
36
Multipartite genome
a virus with a segmented genome which is divided between two or more molecules of nucleic acid. Ex: reoviridae, bunyaviridae
37
Bipartite, tripartite and quadripartite genome viruses
information is divided among two, three and four genomic molecules, respectively
38
Bunyaviridae
all genomic segments packaged into one particle (virion) Negative/ambisense sense, multipartite RNA Genus Tospovirus
39
Reoviridae
Double-stranded, multipartite RNA genome | The 10-12 pieces of genomic RNA are encapsidated within a single virion
40
(+) ssRNA viruses
do not have envelopes and have monopartite, bipartite or tripartite genomes ``` bromoviridae comoviridae sequiviridae tombusviridae ourmiavirus etc... ``` Bromoviridae and comoviridae= free nucleocapsids -All nucleocapsids must be there for the insect to be able to transmit it into plants
41
(-) ssRNA viruses
Rhabdovirus & Bunyavirus are enveloped are transmitted by insects members of both families infect both plants and animals.
42
dsRNA viruses
Reovirus Family | members encompass plants & animals
43
ssDNA
Geminiviruses and Nanoviruses no close animal virus relatives replicate by a rolling circle mechanism like members of the Microviridae (phage)
44
dsDNA
Caulimoviridae (pararetroviruses) - show genomic organizational similarities to Hepadnaviridae replicate via reverse transcription
45
Virus Properties
Plant viruses are often simpler than animal viruses May have ss or ds RNA or DNA genome - most plant viruses have ssRNA genomes
46
Host Ranges
Presentation of disease system is the main differentiation between plants
47
Plant Responses
Non-host response (non-host resistance) Host resistance (either active/constitutive) Systemic Acquired Resistance (included) (SAR) Transgenic Resistance
48
Non-host response (non-host resistance)
Plant is immune, no or limited viral replication occurs, no cell-to-cell movement, no systemic movement most common one mechanism we know: PTGS (post transcriptional gene silencing)
49
PTGS (post transcriptional gene silencing)
A type of defense system that operates at the nucleic acid level but the specificity is not genetically programmed 1. dsRNAs processed into small interfering RNA (siRNAs) by Dicer (enzyme, RNase III-like). 2. siRNAs are incorporated into an RNA-induced silencing complex (RISC) to guide degradation of complementary mRNAs 3. RISC moves systemically throughout the plant and is associated with the accumulation of 21-23 nt RNAs
50
What elicits PTGS for virus resistance?
dsRNA (dsRNA from mRNA, dsRNA viral genomes, replicative intermediates, viroids) mRNA from Hairpin sequences of DNA Excess amounts of RNA
51
Viral Silencing Suppressors
Mechanism of how and where each gene suppresses silencing varies among viruses in different genera or families Effectiveness (“strength”) of the suppressors vary
52
Host Resistance
either active or constitutive Plant genes that confer resistance to viruses= R genes Most commercial development uses this type of resistance
53
mechanisms of R genes (host resistance)
R gene may be an active response to a viral protein R gene may be the absence of a host factor necessary for replication or transport R gene may code for a host factor that contains a mutation that prevents completion of the viral infection cycle
54
Host Resistance- active
only turned on after infection with the virus response is mediated by a single gene which is turned on by a specific viral protein
55
Host Resistance- constitutive
always present Each resistance gene is limited to viruses within a species or genus, does not have any effect with most plant viruses
56
Systemic Acquired Resistance
Active response by host in response to damage that cause necrotic cell death, resulting in diminished susceptibility to later pathogen attack. not specific for the virus and responds to many viruses Plants produce protective compounds, at the site of the attack or systemically to protect distant and as-yet unchallenged tissues. Resistance is not that strong, but can reduce symptom severity resistance can be induced by elicitors other than viruses ex: dispersal of salicylic acid = increased resistance to further infection
57
Plant Activators (Elicitors) of SAR
have no direct effect on pathogens induce plants to produce natural disease-fighting compounds ex: Acibenzolar (Actigard) Biological control organisms (plant growth promoting bacteria) Salicylic acid 2,6-dichloroisonicotinic acid (present in some insecticides)
58
Transgenic Resistance
Engineered resistance and tolerance to plant viruses Uses transgenes derived from a wide range of organisms - plant-derived natural R genes - pathogen-derived transgenes - non-plant and non-pathogen-derived transgenes Coat protein gene: + mRNA with - RNA
59
Control of Vectors
insecticides reflective mulches screens & nets soil fumigation
60
Exclusion of Plant Viruses
quarantine and certification of imported plant material | virus- free certification of seed root stocks, fruit tree propagative material
61
avoidance of plant viruses through cultural practices
timing of plantings removal of old plantings roguing infected plants elimination of alternate hosts of the virus
62
physical barriers
plastic covers insect proof screen UV absorbing plastic and screens

General Virology- Exam 3 (6 decks)

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