- 2- versions of the non-structural replication protein and - 2 protiens translated from subgenomic RNAs

Section 5 Flashcards by Sarah Ahmed Duraid

Plant viruses have the longest history in virology because

first virus discovered is the TMV (tobacco mosaic virus)

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Most plant viruses are ______ genomed and there is no normal dsDNA viruses

RNA

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plant viruses have diff particle morphologies but high occurrence of _________ structures
and some are related to animal or protist viruses

filamentous

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Plant virus common characteristics:

1- most plant virus capsids are made of single protien
2- most are icosohedral
3- most have evolved to get their lipid layer from the cells membrane
4- most geminate making “pairs” of two capsids that come together

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Some plant viruses are shaped like a bacillus (rod) called ________ that are helical and filamentous

bacilliform

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TMV characteristics

1- perfectly regular helical shape
2- showed that RNA encodes protein
3- good model virus
4- very stable
5- replicates to high density and easy to purify a lot
6- has ONLY two components: RNA genome and capsid protien

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packaging of TMV does not start at the end but rather, the RNA has a specific sequence that makes ________ where it goes in first

hairpins

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TMV packaging stages

1- RNA specific structure forms hairpin
2- hairpin goes in and forms into a helical structure as protein (capsid) wraps around the outside
3- RNA is fed through the bottom of the capsid as it assembles toward the 5’ end

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TMV will spontaneously assemble in vitro when the RNA and capsid protein are mixed together meaning no ____ are required

cofactors

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TMV is a great example of efficient use of limited genome size because it encodes _____ different proteins that are

4 different proteins:
2- versions of the non-structural replication protein
- short version ORF1 is a helices required for efficient replication
- long version ORF2 has RdRp region for RNA synthesis**

** (made in smaller amounts cuz ribosome passes through stop codon after ORF1)

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the 4 protiens are:

2- versions of the non-structural replication protein

and

2 protiens translated from subgenomic RNAs

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2- versions of the non-structural replication protein are:
(for making -ve sense RNA)
(don’t go into cell)

short version ORF1 is a helices required for efficient replication
- long version ORF2 has RdRp region for RNA synthesis**

** (made in smaller amounts cuz ribosome passes through stop codon after ORF1)

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2 protiens translated from subgenomic RNAs means:

this means translation of ORF1-2 from the genomic RNA
needs to happen after infection, and then the RdRp can make
a –ve sense version of the RNA and the sub-genomic RNAs
can be transcribed from that -ve sense copy by RdRp
individual promoters before those ORFs for their transcription

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2 protiens translated from subgenomic RNAs are

CP = capsid protein, MP = movement protein

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How do viruses move within plants?
(not like animals where they spread within the host as assembled particles)

initial local movements between
neighboring cells (without even making complete virions) by MP
followed later by systemic transmission through the plants’ circulatory system (phloem)

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what does MP “movement protein” do?

MP = movement protein: allows infection of neighboring
cells by transporting the viral RNA between cells

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what happens if virus that does have ORF for CP gets injected?

can spread to neighbouring cells within
the plant but there will not be a systemic infection

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viral RNA moves through plant cell structures called __________ (with the requirement of MP)

plasmodesmata

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neither the MP nor viral RNA can pass through
plasmodesmata on their own but when ________, they get through

together

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MP binds to the viral ssRNA in
_______ regions to move them between plasmodesmata

non-folded

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some spherical viruses move between
cells as complete __________
where MP forms a ______ through the
plasmodesmata

nucleocapsids
tube

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Cucumber mosiac virus fun facts (2):

largest host range of any known virus (infects >1200 species of plants)
infects crops worldwide and is a problem for agriculture

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why is cucumber mosaic virus a good model virus

can infect cells by injecting RNA (without having to make virus particles)
high yields of particles
infects plant cell protoplasts (plant cell cultures, don’t need whole plant)

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Cucumber mosiac virus genome is

+ve ssRNA segmented genome
RNAs 1, 2, ,3 required for infection

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Cucumber mosiac virus also makes

also makes subgenomc RNAs during infection for protein synthesis

Cucumber mosiac virus: RNAs 1 and 2 are _____ ______ whereas RNAs 3 and 4 are also _____ _______ (RNA 4 can be made, doesn't need to come in virion "sub-genomic")

packaged together

Cucumber mosiac virus needs 3 visions to be transmitted for infection making it a ___-______ ____

multi-partite virus (segmented genome)

cellular enzymes think CMV RNA is tRNA and add an amino acid to it because

3' ends of CMV fold into tRNA like pseudoknot

CMV folding into tRNA like pseudoknot to trick the cell for many reasons (3):

1. protect RNA from being degraded by nucleases 2- increase translation of RNA 3- help avoid RNA replication on RNAs that are being translated

CMV encodes ___ proteins

FIVE

the five CMV protiens are

2 replicase 1 movement within plant and immunity against host defences 1- movement 1 capsid

where does CMV RNA replication occur?

in membrane vesicles attached on the inside of cells vacuole (gas chamber) (membrane vesicles made by viral proteins and they bring the RNA template there)

How does CMV RNA replication happen in membrane vesicle

replicase interacts with sequences in 5' and 3' region of the RNA to initiate replication (also requires host protiens)

WHY does CMV RNA replication occur in membrane vesicles

to keep viral RNA out of cytoplasm and away from anti dsRNA defense

Turnip Yellow Mosaic virus also uses intracellular vesicles to replicate, the vesicle is

outer membrane of chloroplasts

TMV makes vesicles in

endoplasmic reticulum

replication in vesicles is an old strategy as it occurs in primitive cells (ancestors of plants) such as ______ that replicates in vesicles around edges of ER

HaRNAV (relative of polio) infects unicellular photosynthetic protists

_________ forms harmful algal blooms and releases a toxin that kills fish

HaRNAV

Geminiviruses (NEW!) increase packaging size of their simple visions because they have

2 icosahedrons fused together

Geminiviruses (due to their 2 fused icosahedrons)

can package -3000 bases of circular ssDNA and increase the amount of nucleic acid they can package (some are made of 2 pieces of DNA each in separate capsids and both need to be transmitted for infection)

some Geminiviruses are made of 2 pieces of DNA each in separate capsids and both need to be transmitted for infection making them ALSO _____-______

multi-partite

Geminiviruses do not encode their own _____ so so are dependent on the host enzymes DNA polymerase for synthesis of the dsDNA version from ss genome that enters the cell from virion

polymerases

once Geminiviruses use the cells DNA pol to make dsDNA from the ssDNA that enters the cell, this dsDNA then becomes: (2 things)

1- template for transcription (by host RNA pol) 2- replication of more ssDNA genome copies for packaging into new virions

Geminiviruses have ___________ _____ that go in two directions away from the intergenic region (IR, top)

overlapping genes

________ _______ (IR) contains (no protein coding) important sequences for replication and gene expression

intergenic region

commonalities of geminivirus with TMV and CMV, even though it is a ssDNA virus as opposed to RNA

MP CP and Replication protein(s) (don't do the replication but make it happen)

Key viral protein for geminivirus is _____ that brings cells host DNA pol to perform rolling circular replication

Rep

after Rep is done, it displaces the __ _____ _______ circles that are packaged

+ve ssDNA

Rep binds to a specific sequence in ____ near the stem loop structure and it makes a _____ in the loop portion making the 3' end needed for DNA synthesis

IR cut

IR also has promotors for transcription called _________ boxes on both sides to allow gene expression in two directions

TATAA

after completion of a replication cycle, +ve sense DNA circle (template) gets sent back (released) and new stand gets ______ by Rep to make it into a closed circle (can be packaged or used to make more DNA)

ligated

________ have 10 individual ssDNA circles that make up the genome and package each into its own icosahedral capsid

nanoviruses

plant cells have thick walls which makes it difficult for a virus to get through so they use _____ _______ to break through the plant cell wall and allow transmission

other organisms (ex. insects that feed on plants, ex. worms)

The transmission insects for each viruses are very ____ and _____

specific and limited (ones that feed on that plant)

transmission of plants can also occur vertically through:

seed via infected pollen or ovule

Types of insect transmitted plant viruses

propagative non-circulative circulative

Some plant viruses replicate in plant AND in transmission vector species called __________

propagative

Others just stick to the mouth part of the insect and get transmitted to the next plant it eats called ____-______

non-circulative

finally, some intermediate ones move within the insect and pass through cells and tissues but don't replicate in insect called _________

circulative

Insect transmitted viruses need to be able to interact with _____ ______ cells AS WELL AS the _______ that will carry them by having receptors for that vector on their capsid

plant host vector

Cucumber necrosis virus (CNV) is transmitted between plants by _____

Fungus

sub viral pathogenic agents common in plants are (2)

satellites viroids

satellites

- require helper virus for replication (but they are not required for the replication of the helper virus and they don't share sequence homology with it) - do not encode their own protiens for replication (in plants)

satellite viruses

encode their own capsid protein that packages the genome but need help for replication

satellite nucleic acids

packaged in helper protein capsid

satellite are _____ of helper

parasites

satellites effect the diseases caused by helper sometimes __________ it and sometimes ________ it

attenuating it making it more severe

satalties are not a ___________ taxonomic group they have dsRNA ssDNA and circular ssRNA

homogenous

satellite tobacco mosaic virus (STMV) has ________ genome and and has 3' untranslated region UTR similar to that of TMV so that when TMV replicates it replicates the satellite too by accident

ssRNA UTR

STMV encodes 2 proteins:

1- unknown function 2- capsid

STMV causes _________ disease symptoms of TMV

enhanced

there are satellites that don't encode proteins but compete w viral RNA for replicase enzyme and packaging called _________

non-messenger satellite RNAs

non-messenger satellite RNAs example folds into structure that is recognizable by CMV replicase

satelite cucumber mosaic virus

Viriods:

- only exist as generic material (not packaged inside capsids) - exist as ssRNA molecules - get transmitted mechanically (attached through something and penetrate the cell wall) through machines etc

viroids are _______ but fold to look like double stranded RNA circle (rod shape)

ssRNA

you can tell viroids by their sequences

beneficial plant viruses (2)

1. endogenous pararetroviruses: (package DNA) and protect against infection by exogenous pararetroviruses 2. plants infected with some viruses are more resistant to cold temps 3. virologists found a fungal virus that is beneficial to plants (grass can survive over 50 deg if it has been infected by fungal virus)

Section 5 Flashcards

(77 cards)