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Year 1 Biology Ellie M > Plant Virology > Flashcards

Plant Virology Flashcards

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1
Q

Where was wheat domesticated?

A

Near East

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2
Q

Where was corn domesticated?

A

Central and South America

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3
Q

Where was rice domesticated?

A

India and China

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4
Q

What is the name for the transition from hunter-gatherers to gamers and herders?

A

Agricultural revolution

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5
Q

How much does the population rise by each day?

A

200,000

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6
Q

How has food production paralleled population increase? (2 ways)

A

Increase the amount of land used to produce food

Increase the amount of food produced per season on the land already being used for agriculture

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7
Q

More than 85% of our food comes from how many plant species?

A

6-8 (mostly wheat, corn and rice)

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8
Q

Info about sweet potatoes

A

One of earliest domesticated plants
Origin: South America
Spread to Polynesia in 8th century AD
Spread to Asia in 16th Century

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9
Q

What are sweet potatoes a good source of?

A

Energy, carotene, ascorbic acid, niacin, riboflavin, thiamin and minerals

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10
Q

Food problems:

A

Very little fertile land left to create new farmland
Yields are being pushed to the limits through Green Revolution and biological/technological advancements
Environmental pressures

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11
Q

Name 5 biological and technological advances that revolutionised farming

A 
Introduction of new crops
Mechanisation
New and improved varieties
Inorganic fertilisers
Pesticides / herbicides
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12
Q

What caused introduction of new crops?

A

Exchange of plants between continents after European voyage of discovery in 15th and 16th centuries

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13
Q

When did mechanisation begin?

A

Middle of 19th century - invention of internal combustion engine

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14
Q

When did application of genetics to plant breeding begin?

What % increase in crop productivity did this bring about?

A

18th/19th centuries

40%

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15
Q

What process was invented that allowed nitrogen fertiliser to be produced?

A

Haber process - combining hydrogen gas and nitrogen gas to produce ammonia

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16
Q

What are further crop improvements have been made?

A 
High crop yield
High nutritional quality
Nitrogen fixation
Drought resistance
Resistance to pests
Insensitivity to photoperiod
Plant architecture
Removal of toxic or unwanted compounds
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17
Q

What is plant architecture?

A

Positioning of leaves, branching pattern of stem, the height of the plant and positioning of organs

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18
Q

When was the Irish potato famine and how many people died?

A

1846-1850

Up to a million

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19
Q

When did brown spot of rice occur and what was it? How many deaths did it cause?

A

1942
Weather favoured H. oryzae, and enabled it to suppress rice yields
Rice prices soared
2 million people died

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20
Q

What was African Cassava Mosaic Disease, when did it occur and what happened?

A

Cassava Mosaic Virus Disease spread across East and Central Africa
1980s - early 1990s
In 1994 alone, up to 3000 people died of famine-related illnesses in Uganda
500 million people relied on cassava

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21
Q

What was the first identified virus, and who discovered it in what year?

A

Tobacco mosaic virus
Beijerinck
1898

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22
Q

What is chlorosis?

A

Yellowing of leaves

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23
Q

What was tulipomania?

A

A morphogenetic disturbance of tulips caused pink petals to be bleached white, but with a pink tinge on the edges. These tulips became so valuable that in 1625 they were worth tonnes of grain or many cattle

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24
Q

Definition of a virus:

A

Gibbs & Harrison, 1976

A small transmissible parasite, with a small nucleic acid genome which needs host cell components for multiplication

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25
Q

How small are virus particles?

A

If 10 million particles occupied one plant cell, they would only occupy 1% of the cell’s space

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26
Q

What is the abbreviation for tobacco mosaic virus?

A

Tobamovirus

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27
Q

What are the four types of nucleic acid?

A

Single-stranded (ss) positive sense RNA
Single-stranded (ss) negative sense RNA
Double-stranded (ds) RNA
DNA viruses

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28
Q

What is single-stranded positive sense RNA?

A

This type of genome is ready to function as messenger RNA on entry into the host cell, and is usually infectious. It can be directly translated into the desired viral proteins

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29
Q

What is single-stranded negative sense RNA?

A

A negative sense genome has to be copied into positive sense before it can function. It does not encode mRNA. This copying is carried out by a viral-encoded enzyme found in the virus particles

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30
Q

What is double-stranded (ds)RNA?

A

Viruses with dsRNA also contain a viral encoded enzyme which copies the genomic RNA into mRNAs

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31
Q

What are DNA viruses?

A

These plant viruses use host enzymes to produce functional mRNAs. These DNA viruses are therefore able to initiate infection in the absence of viral-encoded proteins

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32
Q

What percentage of all plant viruses are positive sense ssRNA?

A

75%

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33
Q

Give an example of a DNA virus with double-stranded DNA

A

Caulimovirus (cauliflower mosaic virus)

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34
Q

Give an example of a DNA virus with single-stranded DNA

A

Geminivirus (maize streak virus)

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35
Q

What is a viroid?

A

Unencapsidated, small, single-stranded RNAs which replicate when inoculated onto plants. They code no protein, and have extensive internal base pairing which gives them rod-like secondary structures. Smallest infectious pathogen known. Classed as a ‘subviral agent’

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36
Q

Give two examples of viroids

A

Potato spindle tuber viroid

Coconut cadang-cadang viroid

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37
Q

Info about potato spindle tuber viroid

A

Natural hosts are potatoes and tomatoes
No form of natural resistance
Symptoms most severe in hot conditions
359 nucleotides

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38
Q

List plant virus symptoms

A 
Local lesions
Chlorosis
Mosaics
Necrosis
Morphogenetic disturbances
Effect on plant size
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39
Q

What is a local lesion?

A

A localised area of diseased tissue (chlorotic or necrotic). The virus is restricted to the necrotic lesion and a few layers of cells at the outer edge

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40
Q

What are mosaics?

A

Yellowing of leaves on a green background. In monocotyledons, a common result of virus infection is the production of stripes or streaks of tissue lighter in colour than the rest of the leaf

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41
Q

What is necrosis?

A

Tissue death, either by stress or via specific plant virus infections

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42
Q

What are morphogenetic disturbances?

A

‘Messed-up’ plants, parts of plants or organs. Growth reduction, colour deviation, wilting, malformation of specific organs, premature leaf drop or curling - all indicative of of aberrant (diverging from the normal type) hormone metabolism

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43
Q

What is synergism?

A

The association of two or more viruses acting at the same time

44
Q

An example of synergism

A

Tobacco mosaic virus and potato virus Y acting together in Surfinia

45
Q

Name some invertebrate vectors (with Latin names) of viruses

A

Whiteflies (Aleyrodidae - family)
Aphids (Aphididae - family)
Nematodes (Nematoda - phylum)

46
Q

Whiteflies as vectors

A

Aleyrodidae
Known to transmit about 70 serious disease agents, mainly of tropical and subtropical plants. They cause problems in greenhouses in colder climates. African cassava mosaic virus is transmitted by whiteflies

47
Q

Aphids as vectors

A

Aphididae

Very successful exploiters of higher plants. They transmit about 66% of viruses with invertebrate vectors

48
Q

Nematodes as vectors

A

They transmit several widespread and important viruses via the soil. They feed on root epidermal cells which can contain virus particles

49
Q

What species of Nematodes transmit Nepoviruses (genus of viruses)?

A

Xiphinema (‘dagger nematodes’ - long stylets to reach tissue of plants)
Longidorus (transmit cacao necrosis virus)

50
Q

What species of Nematodes transmit Tobraviruses (genus of viruses including the species ‘Tobacco rattle virus’)?

A

A species of Trichodorus (genus)

51
Q

Why are nematode vectors so hard to control?

A

Pesticides only kill insects so they cannot spread viruses as easily, but it is very hard to kill nematodes in the soil

52
Q

Besides invertebrates, what is another vector of plant viruses?

A

Fungal vectors

53
Q

Give an example of a furovirus

A

Soliborne wheat mosaic virus

54
Q

How are furoviruses such as the soliborne wheat mosaic virus transmitted? How long can the vector survive?

A

In the resting spores of the plasmodiophoromycete vectors

In these spores the virus may survive in air-dried soil for many years

55
Q

What species of fungus transmits tobacco necrosis virus (TNV)?

A

Olipidium brassicae

56
Q

How does Olipidium brassicae transmit viruses? How long can the vector survive?

A

The viruses are carried in the surface of spores

The zoospores carrying a virus can survive only a few hours

57
Q

What is Rhizomania and what is it transmitted by?

A

A disease of sugar beet caused by the virus beet necrotic yellow vein virus (BNYVV)
Transmitted by the fungus Polymyxa betae

58
Q

Why is it called Rhizomania?

A

It comes from the extensive proliferation of lateral roots, and also necrosis of vascular bundles and severe stunting of plants

59
Q

What % loss of yield does beet necrotic yellow vein virus cause?

A

80%

60
Q

What is mechanical transmission of viruses?

A

The introduction of infective virus or RNA into a wound made through the plant surface

61
Q

What are some examples of plants that use mechanical transmission?

A

Tobacco mosaic virus (TMV) and potato virus X (PVX)

Neither have insect vectors

62
Q

How does sexual transmission work?

A

Virus transmitted through the seed of infected host plants
Viruses can persist in seeds for long periods of time, so that commercial distribution of seed-borne viruses can occur over long distances

63
Q

What is an example of how a seed can become infected with a virus?

A

Sexual transmission via pollen

64
Q

What fraction of plant viruses are transmitted via the seeds of host plants?

A

1/5

65
Q

What are the different methods of virus transmission in plants?

A 
Sexual transmission
Mechanical transmission
Fungal vector
Invertebrate vector
Bacterial vector
66
Q

Who discovered tobacco mosaic virus and when?

A

Adolf Mayer, a German agricultural chemist working in Holland. He classified it as a ‘mosaic disease of tobacco’ and failed to culture it
1886

67
Q

How was it proved that TMV was a disease smaller than anything previously described?

A

In 1892 Russian scientist Dimitrii Ivanovsky was studying TMV and reported that the sap of infected leaves remained infectious even after being filtered through Chamberland filter-candles (has pores smaller than bacteria)

68
Q

How was the virus finally recognised?

A

In 1898, Martinus W. Beijerinck showed the infectious agent was able to replicate in leaves but not in filtered solutions

69
Q

What are the firsts TMV is known for?

A

The first virus to be shown to consist of RNA and protein
The first virus to be characterised by X-ray crystallography
The first virus to be used to be used for electron microscopy
The first virus to be used for solution electrophoresis and analytical centrifugation

70
Q

What is the size and shape of TMV? What is it’s genome like?

A

18 x 300 nm rigid rods
Positive sense ssRNA genome
6395 nucleotides
Encodes 4 viral proteins

71
Q

What does TMV have at the 5’ (5 prime) end?

A

5’ CAP - a methylated guanine nucleotide

The same as in normal eukaryotic mRNAs, where ribosomes bind and begin translation

72
Q

What does TMV have at the 3’ terminus?

A

A tRNA-like structure (folded RNA secondary structure) which is unlike eukaryotic mRNAs, which have a poly(A) tail at the 3’ terminus

73
Q

What is the purpose of a poly(A) tail

A

It stops RNA being eaten by enzymes so provides protection in eukaryotes

74
Q

How does translation work in eukaryotes?

A

The ribosome moves along the mRNA strand and when it reaches a stop codon at the end of an open reading frame it ‘falls off’ the sequence and cannot bind to the RNA further down the sequence

75
Q

Why is eukaryotic translation fine for eukaryotes?

A

Because each mRNA strand only codes for one protein

76
Q

Why is eukaryotic translation a problem when translating viral RNA?

A

The one piece of single-stranded positive sense viral RNA codes for 4 proteins, so as a result there are silent / untranslatable open reading frames - the second open reading frame can never be translated, meaning that only one protein can be produced each time

77
Q

What are the 4 proteins encoded for by viral RNA - what size are they and what is their purpose?

A

183kDa - replicase enzyme
126kDa - replicase enzyme
30kDa - transport protein
17.5kDa - coat protein

78
Q

What is the solution that allows ribosomes to encode both the replicase proteins?

A

The genomic RNA acts as mRNA for a 126kDa protein, and about 10% of the time the ribosome reads through a ‘leaky’ stop codon (UAG), meaning that the RNA sequence continues to be translated until the 183kDa protein is produced

79
Q

What are the replicase proteins also known as?

A

RNA-dependent RNA polymerases - both required for replication

80
Q

The 30kDa and 17.5kDa proteins cannot be translated from genomic RNA as both open reading frames are internal - not at the 5’ end of the molecule. How are they translated?

A

The virus must generate sub-genomic RNAs with the open reading frames at the 5’ ends

81
Q

In the replication of TMV, what type of RNA do the replicator proteins attach to and what type of RNA do they produce?

A

They associate with the 3’ end of the positive sense viral RNA and produce negative sense RNA

82
Q

What type of RNA, produced by the replicator proteins, acts as a template to produce both full-length positive sense RNA and positive sense sub-genomic RNA?

A

Negative sense viral RNA

83
Q

How do viruses move between cells in a plant?

A

They move through plasmodesmata, and travel in the phloem to other areas of the plant

84
Q

What is the problem encountered by viruses when they try to move between plant cells?

A

The virus particles are too large to travel through plasmodesmata

85
Q

How do viruses solve the problem of being too large to travel through plasmodesmata?

A

Viruses encode the 30kDa movement protein, which moves towards the plasmodesmata, binds to it and expands it. It then chaperones the virus particles through the plasmodesmata

86
Q

What are the role of the 17.5kDa coat proteins?

A

They encapsidate the genomic RNA and form the virus particle

87
Q

What are the 3 ways to prevent virus epidemics?

A

1) Plant healthy seeds/tuber that are tested to ensure they are virus-free. However, this is expensive and labour intensive
2) Keep plants virus-free e.g. by using insecticides to kill insect vectors
3) Use virus resistant plants by breeding them to be resistant. However, these can take years to produce and viruses can mutate rapidly to overcome this

88
Q

What is cross-protection?

A

Mild strains of viruses inoculated onto plants to prevent more virulent strains from infecting the plant

89
Q

Who first demonstrated cross-protection and when?

A

McKinney

1929

90
Q

What is the issue with cross-protection?

A

Viruses can mutate and viruses may not be mild any more if they do

91
Q

What is the benefit of plant genetic engineering to induce resistance to viruses?

A

Every cell would express the coat protein of the virus like any other plant gene

92
Q

How would it be possible to achieve expression of a viral gene from the plant’s nucleus?

A

Clone the viral gene as double-stranded cDNA then insert it into the plant’s chromosomes within the nucleus, ‘transforming’ the plant

93
Q

What bacteria allows us to transform plants?

A

Agrobacterium

94
Q

How does agrobacterium transform plants?

A

It binds to a plant cell and enters the cell’s nucleus, then inserts its genes into the nucleus

95
Q

Why does Agrobacterium insert its DNA into plant cells?

A

It does this to cause tumours that it can feed off, hence it can be used to insert other desired genes into plant DNA such as virus resistance

96
Q

How is the desired gene placed in the bacteria?

A

In a DNA section called a plasmid, which as transferred into the bacterium

97
Q

How is the transferred gene activated, causing the plant to develop the desired trait?

A

A ‘promoter’ (a trigger which activates the gene), is included with the desired gene on the plasmid. The promoter activates the transferred gene

98
Q

What must be done to viral RNA genes to insert them into the plant genome?

A

They must be converted to DNA

99
Q

What is an example of a promoter which allows plant expression of the TMV coat protein?

A

CaMV35S

100
Q

Who first transformed plants and when?

A

Powell-Abel et al.
1986
Transformed TMV plants more resistant to TMV infection and symptom development was delayed in progeny

101
Q

What is the name for when a plant expresses viral coat proteins and is resistant to the virus?

A

Coat protein-mediated resistance (CPMR)

102
Q

How does coat protein-mediated resistance work?

A

When a virus infects a non-resistant plant, the viral coat proteins relax to expose viral RNA and allow ribosomes to attach
In a transgenic plant, when the viral RNA is exposed, coat proteins identical to that of the virus but produced by the plant itself should rapidly bind to the viral RNA, so a ribosome can’t attach to the RNA and there is no virus translation

103
Q

What risks are associated with transgenic CPMR plants?

A

The plants’ DNA contains antibiotic markers, to select which plants had been transformed - could spread antibiotic resistance
Plants will be expressing the viral coat protein - is this foreign protein safe to eat?
Plants will also contain viral sequences - the sequences may interact with another unrelated virus and make the symptoms worse (synergism)

104
Q

What is an example of a species of bacteria that produces proteins that kill insect larva if they ingest the proteins?

A

Bacillus thuringiensis

105
Q

What protein does Bacillus thuringiensis produce, and how does it kill insects?

A

Bt protein

It causes severe damage to insect larvae guts, so they die of starvation

106
Q

Why can’t Bt protein be sprayed or used as powder on plants?

A

It is not stable after it is dusted onto a plant, and it only works on insect larvae that live on the surface of plants, not those in plant tissue or the soil.
The spray may also drift into neighbouring areas and cause damage

107
Q

What is the alternative possible way to use the Bt protein?

A

Genetically engineer plants to express their own Bt gene, killing insects anywhere near the plant. It is also cheap, stable and environmentally friendly

Year 1 Biology Ellie M (28 decks)

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