Unit 4 Plant Virus

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Unit 4 Plant Virus
Dr. Mingmin Zhao April 8, 2008
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CONTENTS

• Introduction
• Symptoms
• Structure and composition
• Transmission of plant viruses

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What is virus?
1. Introduction

• Virus is a molecular parasite(???)
• Every virus carry proteins and nucleic acids in a
  protective coat. This protective membrane is
  called the capsid(??).
• Viruses consist of a nucleic acid core and a
  protein coat.

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Characteristic of a virus

• Very small
• The big difference between viruses and all else,
  is that fact that viruses are so small that they
  can not be viewed without the help of an electron
  microscope.
• This is because viruses are, on average, smaller
  than a regular wavelength of visible light.
• They can not be seen by the naked eye or a
  regular microscope.

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• Viruses are so small in fact, that the largest
  virus is equal in size to the smallest bacteria.
• The smallest virus measures only 20 nanometers in
  length.

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Shape

• Shape is also a defining characteristic of
  viruses.
• The basic shapes are rods, filaments, crystals,
  helixes, polyhedrons and spheres, with added
  extensions.

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• strictly parasites
• Viruses are not classifiably alive or dead. They
  seem to be in limbo between each state.
• Viruses exist this way because they are strictly
  parasites???.
• That is, they can not survive and thrive without
  a host or group of host cells. The hosts provide
  viruses with all the chemicals and molecules they
  need to survive and reproduce.

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• Viruses can lie dormant within any host or
  environment until the proper conditions for their
  activity are provided.
• This is why we sometimes say that viruses have
  incubation periods of certain lengths.
• For exampleTMV (60 years)

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• Plant viruses attack only plants. They are
  harmless to all other organisms.

• Prevention is the only economic control for
  virus diseases.

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History major events
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Charles de Lieclase (1576) described broken tulip
flowers

• The first record of the symptoms of a plant virus

broken tulip flowers. In Holand
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• so attractive that
• a tulip bulb is equal to several beef
  cattle, pigs, sheep,
• several tons of grain, thousands pounds of
  cheeses and a mill.

????????Rijks?????????1619?????????????????
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The first breakthrough in 1886

• Adof Mayer, TMV
• The healthy plants could be infected by injecting
  their leaf veins with sap taken from diseased
  plants.
• He made a conclusion that the disease was the
  manifestation of a bacterium.

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In 1892, Dimitrij ivanovsky

• Published the results of his study on mosaic
  disease of tobacco.
• He confirmed Mayers report of the
  sap-transmissible nature of the disease
• Further showed the sap to remain infectious even
  after passage through bacteria-proof filter.
• Claimed the causal agent to be a microbe.

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The Father of virology----Dr.Martin Berjerinck

• Base on all the findings, he concluded in 1898
  that the mysterious pathogen was not a bacterium
  but a contagium virum fliudum.
• He thought the contagium to be able to reproduce
  itself in living plants and referred it as a
  virus.
• Therefore, he is rightly considered as the Father
  of Virology.

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Stanley(1935),breakthrough conserning the nature
of plant virus

• Used the newly introduced methods for isolation
  and characterization of enzymes and other
  proteins for purifying TMV.
• He succeeded in isolating it as a proteinaceous
  crystalline substance.
• Was awarded the Nobel Prize for his achievement.

Wendell Meredith Stanley(1904-1971)
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Frederick Charles Bawden (1936), RNA

• Reported TMV containing 5 RNA and 95 protein.

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Kausche, Pfankuch and Ruska(1939)

• Took electron microscope picture of TMV, being
  the first of a plant virus.

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Economic Impact of Plant viruses

• Affect most economic crops, causing reduction in
  yield or quality of the production. Especially in
  tobacco and potato.
• There are 50 plants of the family Solanaceae
  (??) and Cruciferae(????) could be infected by
  plant viruses.
• In flower, causing reduction in yield or quality
  of the production, even affecting the import and
  the export.

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• There are many examples of severe crop losses due
  to virus disease.

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• Cacao swollen shoot virus (CSSV) has been a
  menace to the cacao plantations in West Africa.
  In Ghana more than 100 million cacao trees have
  been cut down since 1945 just to stop the spread
  of the disease.

??????
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• Sugar beet crops in Europe and America have
  suffered serious losses due to sugar beet yellows
  for many years.
• Total losses due to sugar beet yellows in
  Britain in 1957 were about 1,000,000 tons.

??????
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• In India, the losses in potato yield have been
  estimated to be 40-85 due to potato virus Y.

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The utilization of plant viruses

• As a vector in Biotechnology
• It could be used to study the fundamental issues
  in life science.

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Biotechnology

• Plant viruses can be used both to express new
  genes and to inhibit expression of selected genes
  in plants.
• An example of specific gene inhibition (gene
  silencing) is shown to the right.

• A normal pea plant is shown above.
• Below you see the effect when a plant virus is
  used to inhibit expression of a gene involved in
  chlorophyll(???) stabilization.
• When this gene is inhibited the chlorophyll is
  degraded and the plant becomes white.

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2. Virus symptoms

• symptoms? No sign
• Virus infected plants can display a wide range of
  different symptoms.The whole plant can be
  stunted (dwarf-like) and infected leaves can show
  abnormal colorations like mosaics and yellowing.
• Very often infected leaves have a rolling or
  curly appearance.

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Mottling

• If leaves display a pattern of abnormal
  coloration this is referred to as a
  mottle.Mottling can be both light and dark.
• A mottle can be necrotic (dead tissue) and when
  spread to many leaves it is referred to as
  systemic necrosis

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light
Yellow mottling in leaf of naturally infected
Potato mop-top virus
???????
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dark
Cherry Rusty Mottle Virus (CRMV)
???????
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systemic necrosis

• Broad bean (Vicia faba) with systemic necrosis
  due to infection with alfalfa mosaic virus (AMV).

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Mosaic
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• Bean (Phaseolus vulgaris) infected with bean
  yellow mosaic virus (BYMV).

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• Leaf from dahlia (Dahlia x hortorum) infected
  with dahlia mosaic virus (DMV).

???????
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• In monocots,mosaics usually consist of elongated
  light areas referred to as "streaks" or "stripes".

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• Soil-borne cereal mosaic virus (the disease
  formerly known as Soil-borne wheat mosaic virus)

????????
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Beet yellows virus

• Leaf yellowing and necrotic spots in an old leaf
  of field-infected sugar beet.

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• Plants infected with lettuce infectious yellows
  virus. (?????????)

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Vein clearing

• In some viral diseases,veins become light and
  more distinct.

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Leaf spots

•   Some infections are associated with leaf
  spots. Often some of the spots are ring formed -
  these are simply referred to as ring spots.

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• Spotting of tomato leaves caused by tomato
  spotted wilt virus(??????).

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• Yellow ring spots on apricot(?)

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• Impatiens with impatiens necrotic spot virus
• (????????)

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Leaf rolling and curling
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• Leaf roll (Potato Leaf roll Virus/aphids)

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Stunting

• Stunting (or dwarfism ) is the most common
  symptom associated with a virus infection and
  sometimes it is the only observable sign of
  infection.

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• Healthy plant (left) and plant stunted by tomato
  spotted wilt virus.

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3. Virus structure and composition

• Virion, virus particle

geminate
Bullet-shaped
Rod-shaped
Spherical (20-35 nm)
Thin filamentous
filamentous
bacilliform
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Structure of rod-shaped virus Helical symmetry
8nm
TMV
18nm
2100 protein subunits, 130 circles
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Structure of spherical virusIsometric symmetry
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Virus Composition

• Nucleic acids and proteins

Nucleic acids 5-40 Proteins 60-95
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Viral protein

• Viral proteins consist of amino acid.
• The protein shells of plant viruses are composed
  of repeating subunits.
• The amino acid content and sequence for identical
  protein subunits of given virus are constant but
  vary for different viruses and even for different
  strains of the same virus.

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• Coat protein 20 amino acid
• Function of coat protein
• Protecting nucleic acids
• Identifying host
• Antigenic determinants

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Nucleic Acid
RNA and DNA According to their function in the
replication process, they could be divided into 5
types as follows

• Positive single strand RNA, ssRNA
• Negative single strand RNA, -ssRNA
• Double strand RNA, dsRNA
• ssDNA
• dsDNA

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• Monopartite genome a single strand RNA
• Monopartite virus (TMV,potato virus X)
• Multipartite genome several different single
  strand RNA
• Multipartite virus (CMV, AMV)

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4.Virus Transmission
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• Mechanical transmission
• Graft Transmission
• Transmission through seeds and pollens
• Transmission through vectors (more important)

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(?)Transmission through vectors

• Aphids
• White flies
• Mealybugs(??)
• Lesf hoppers and plant hoppers(??)
• Nematodes
• Fungal vectors
• Dodder transmission

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Transmission periods of vectors

• Acquisition period(???)????????????????
• Incubation period(???)????????????????
• ??,???????????????
• Inoculative period(???)??????????????
• Retention period(???)???????????????

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Relationship between vector and virus
Based on the viral circulation in vectors

• Circulative(?????)
• ?? ???? ???? ????
• ????
• ???
• ????????????,??????????
• Noncirculative(??????)
• ?????????

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Relationship between vector and virus
According to retention period

• Nonpersistent(????)
• Semipersistent(????)
• Persistent(???)
• ??????????

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Aphids

• Nonpersistent ,
• Virus is easy to be transmitted with plant sap by
  friction.

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Lesf hoppers and plant hoppers

• Circulative
• ??????.
• In general, they couldnt transmit nonpersistent
  virus.
• A few hoppers could transmit semipersistent
  virus.

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Fungal vectors

• Most fungal vectors come from soil.
• For example. ???????????,
• ????(Olpidium)
• ????(Polymyxa)
• ????(Spongospora)
• In addition, ???????????????
• ?????????????
• persistent and nonpersistent

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Nematodes

• ??5?38??????? ??????????????????,????(Dorilaimida)
  ,?????????
• ???????????????(Nepovirus)????????(Tobravirus)??
• ????????????????????????
• ??????(????,?????,??????
• ???,????????)

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(?)??????????

• 1.????(sap transmission)
• ???????????????????????????????,???????
  
• ??????????????????,?????????????
• ????????????????,??????????????
• ???????????????????????,??????????????
  ?

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• 2.????(seed transmission)
• ????????????????????
• ????????????????????????????????
• ?????????????,??????????????

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• 3.????(graft transmission)
• ????????????????????????,?????????????
  
• ????????????????(???)???????????,???????????
  ??????????????????????????

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• 4.?????(dodder transmission)
• ?????????????????,?????????,????????????
  ???????
• ???????????????,?????????
• ?????????????????????????????????????????????
  ????????,???????????

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5. Virus transport

• In order to spread in the plant viruses take
  advantage of the plants own transport system.
• This involves plasmodesmata (????)connecting
  individual cells and the phloem vessels which can
  transport the virus to distant sites in the
  plant.

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• However, virus particles (blue) cannot spread
  through the plasmodesmata unless these are
  modified by the virus.For this purpose plant
  viruses express various movement proteins (red)
  which increases the size of the plasmodesmata.
  Several different mechanisms seems to be
  involved in this process.

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• Virus transport by phloem is very spreading
  quickly.
• Mechanism of distant transport movement protein
  encoded by virus could involve in the transport
  process.
• For example Coat protein of TMV is
  necessary for virus distant transport.
• The direction of virus transport
• Up or down
• consisting with the flowing direction of
  plant nutrition.

TMV transport in tomato
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6. Infection and replication of Plant virus

• ?????????
• ??????????????
• ?????????

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• ????????,?????????????????
• ?????????(replication),?????????????????,???
  ?????(Gene transmission)
• ???????????(gene expression)??????RNA????????
  ??.

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?????????

• ?????????
• ?????????(????????????)??????????????????????????
  ?
• ?????????????????????(Po1ymerase),?????(????)?

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??????????????

• ?????????????????
• ????????????(mRNA)????
• ????????
• ?????????????(???\???????),????????,???????.

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????????mRNA???
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(?)?????????

• ???????????????????RNA????????????.
• ??????mRNA??,????mRNA????????(open reading
  frame,ORF),?????(ATG?????,?????????????,??????????
  , ???????, ??????(TGA,TAA?????),?????

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???????????????????????????,??ssRNA??????????????
??????????

• 1.????RNAs??????3??????????????(sub
  genomic)RNA,???????5????????????????,?????????
• 2.??????????????????????,?????????????????,??????
  ?(polyproteins)????????????,??????????????,????Y??
  ??

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• 3. ???????????????????????,???????5?????,???????
  ????,?????????
• 4. ????(read-through)????5????????????????(1eaky
  ),?????????????????,??????????,??????????????,????
  ???????????
• 5. ?????(trans-frame)????????????????????,???????
  ???(?????????),????????UAG??????????,?????????????
  ??,??????????

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• ??????????????,??RNA????????45?,??????9??????????
  ?????????????????????????????????????????????????
  ??????,??????????,?????(inclusions)?
• ????????????,???????????????

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???????
??????????
??????????
????????????
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(?)?????????????(?)

• ????????????,????????????????????,????????????????
  ???????????,???????
• gene bank??????????????

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7. ??????????

• ???????

• ???????????????????(Committee on Taxonomy of
  Virus,ICTV)?????????
• ????????????????????????????????????????(group),??
  ????????(member)?

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• 1995?,ICTV???????????????,?????????????????????
  ??????????????????????,????????????
• ICTV?????????????????????????

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• ???????????????????,?????????????????????
  ????????????????????????????????????????????????
  
• ????????????(strain)??????????,????????????,
  ?????????,??????(isolate)?

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• ??1995?,?ICTV?????????3600?,?????????788??
• ICTV????????47??,??????11???1??????????5????
• 1.??DNA(ssDNA)????
• 2.??DNA(dsDNA)????
• 3.??RNA(dsRNA)????
• 4.???RNA(-ssRNA)????
• 5.???RNA(ssRNA)????

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• ????????????,???????????????????????????
  ???????,?????????????????,??????????????????????
  ????????????,?????????????,???????????????????????
  ??

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???????

• ????????????
• ??????
• (?????,?????)
• ??????(tobacco mosaic virus,TMV)
• ??????(cucumber mosaic virus,CMV)
• ?????????????,????X??(potato virus
  X,PVX)????Y??(potato virus Y,PVY)??

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• ????????????????????????????,?????????
  ??????,?????????????,??????????????????????67??470
  ?????

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• ??????????????????????
• ?????????
• ?Tobacco Mosaic Tobamovirus
• ?????????
• ???????-virus??,?????????(??????)????????(??????)
  ??virus????,???????
• ??????????Cucumovirus?
• ?????????-viridae?-virales???,????????

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8. ???????????

• ???????
• (?)?????
• 1. ????
• ???????????????????????????????????????
  ??????????????????????????????????????????????????
  ??????????????????????????

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• ????????????,???????,??????????????????,??????????
  ???,??????
• ???????????,??????????

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• 2.??????????
• ????????,????????????(???????????????
  )???
• ?????????????,????????????????,???????
  ?????????????????????

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• ? ????(Thermal inactivation point,TIP)
• ?????????,???????10??????????????
• TIP????????????,??45?
• ??????????,?93?
• ?????????5570??
• ???????????????????,???????????????

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• ? ????(Dilution end point,DEP)
• ?????????,????????????????????????.
• ?10-1,10-2,10-3???
• ???????DEP?10-210-3?
• ?????????????????,????,????????????????
  ?????????????????????????????????????,????????????
  ??

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• ? ?????(Longevity in vitro,LIV)
• ?????????,??2022????,?????????????
• ??????LIV???????
• ????????????????????,???????????????????
  ?,??????????????????

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• (?)????
• ????????,???????????????
• ?????,???????????,????????????????,????????????,??
  ?????????????

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(?)?????

• ??(antigens)?????????????????,???????????
  ???????
• ??(antibody)???????????????????
• ????????????????
• ???(antiserum)????????
• ???????????????,????????????????????????
  ????

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• ??????
• ????,
• ?????(???????),
• ????????

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• ??????(p214)
• ???????(Enzyme LnkedImmuno Sorbent Assay,ELISA)

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(?)???????

• 1 ???????(PCR)
• ???????(Polymerase Chain
  Reaction,PCR)????????????????DNA??????????,???????
  ????????
• ???????????????

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• PCR???????
• (1)?????(??DNA???1???2?Mg2?4?dNTP?Taq
  DNA???)??????(?????DNA???????)
• (2)???)???(???????3???,??????DNA)
• (3)????,??Taq DNA???????5??3???,??4?dNTP???????D
  NA???,??????????????????
• ????????,??????????????DNA??????????

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• ????DNA???20????,??106?
• ?DNA??????????,?????,???????,?????????
  ?????????????,???????????????DNA???

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• ???????????RNA,?Taq DNA??????RNA?????DN
  A?,???????????????,?RNA???????????DNA,????????PCR?
  ?,?????????PCR(Reverse transcription PCR,
• ??RT-PCR)?

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• 2 ????
• ??DNARNA???????
• ??DNARNA??????????
• ?????????????????????(probe)????????
  ??,??????????????

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9. ?????????

• ????????????????,????????????????????
• ????????????????????,????????????,????????????
• ?????????????????????????????????????,???????????
  ???????????,??????????????????????????????????????
  ????????????????

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• ?????????????
• ????????????,?????????????

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• ????(?????)???????????????????????.
• ???????????????????,???????????????
• (1)?????????,????????????????????????????????X??,
  ??????????????????,?????????,?????????????,???????
  
• (2)?????????????????????????????,????????????????
  ???Y??????

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• (3)??????????????????????????????????????????????
  ???????,??????????
• ????????????????????(?????????)?????
  ???????????????

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10. ???

•   ???(Subvirus)?????????????????????.
  1981????Lwoff??.
•  ?????(viroid)
• ????????????????????RNA,??????,?????,???
  ????
• 1971?Diener??????????????????????(vir
  oid)??????????????????????????

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• ???????Chrysanthemum stunt viroid
• Affected flowers in the foreground are also
  showing premature opening and colour break.

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• Chrysanthemum stunt viroid
• Affected flower (right) The flower is reduced in
  size and showing marked colour bleaching.

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• ????????RNA
• ??????,??????????????RNA?,????????RNA,?
  ????????????????,?????,?????????(??????)??????????
  ?????????????(virusoid),????????????RNA(satellite
  RNA,sRNA)?
• ??????????????RNA???,?CMV??RNA??

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• ??????
• ??????????????,??????(??????)????????????
  ????,????????????????????????????????,????????????
  ????????????????????????????????????????????
• ?????????(Satellite tobacco necrosis
  virus,STNV)????????????(Maize white-line mosaic
  satellite virus)??

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? ?

• ????????? ?????????????????,?????????????????????
  
• ?????????RNA??????RNA?????RNA?????DNA?????DNA???
• ???????,??????????(????????,?????????)??????(?????
  ????????)?
• ????????????????????????????

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• ???????(??)?
• ??????????????????????????????????????????????