Choosing the Right CBSE School A Comprehensive Guide for Parents
MCB3707.ppt
1. Plant Viruses
Dr. Ernest Hiebert
Plant Pathology, 1444 Fifield Hall
392 3631 216
ehi@ifas.ufl.edu
2. Introduction
Overview of plant viruses.
Life cycle of a typical RNA plant virus
Genomic organization and replication
strategies of selected plant viruses
How are plant viruses controlled?
3. Relative sizes and comparative virion structures resolved by x-ray crystallography
8. Genus Tobamovirus
ssRNA(+), rod-shaped virion morphology, no known vector
Tobacco mosaic virus
MT = capping,
HEL = helicase,
POL = polymerase,
6395 nts
Cap at 5’
9. Genomic organization and expression of type member
Tobacco mosaic virus of the genus Tobamovirus
•Rod-shaped virions 18 nm diameter and 300 nm long.
•
•Virions very stable.
•Coat protein MW = 17.5 kDa
•No known vectors.
10. Genomic organization and expression of type
member Tobacco mosaic virus of the genus
Tobamovirus
Genome ssRNA, messenger sense, monopartite, 6395
nucleotides, contains at least four genes.
•Capped 5’ end, t-RNA at 3’ end.
•Viral RNA consists of a 5'-end untranslated region of 68
nts.
•Open reading frame at the 5’end codes for a 126 kDa
protein and a readthrough of the UAG terminator signal
by plant suppressor Tyr-tRNA to produce 183 kDa protein.
•Genes downstream expressed via subgenomic RNAs.
Genome expression strategies involve subgenomic RNAs,
and read-through translation
11. How do plant viruses initiate infection?
Virus must enter via a wound in
the plant cell wall and must
be at the site during injury.
15. Virus spread from infection
site
Replication within infected cell
Virions or viral genome move cell-to-cell
via plasmodesmata
Facilitated by a virus-encoded movement
protein.
Long distance movement via vascular tissue
22. Viral translation strategies
Polyprotein synthesis
Picornaviruses- Entire (+) sense RNA genome is translated into a single
large polyprotein. Processing is carried out by two virus encoded
proteases 2A pro and 3C pro.
Flaviviruses- Viral precursor proteins are processed by cellular proteases.
The (+) sense RNA genome is translated into a polyprotein precursor
processed by viral serine protease and by host signal peptidase.
Potyvirus group of plant viruses- Potato virus Y and tobacco etch virus
contain a (+) sense genome RNA of around 10,000 bases which has a
single open reading frame. This polyprotein is processed by viral
encoded proteases.
Potyviruses
Comoviruses
23. Family Bunyaviridae, genus Tospovirus, type member Tomato spotted
wilt virus (TSWV) Negative and ambisense , single-stranded RNA
Negative sense single stranded
RNA virus
25. Family Bunyaviridae, genus Tospovirus, type member tomato spotted
wilt virus (TSWV) vectored by thrips, replicates both in the vector and
in the plant host
28. Family Bunyaviridae, genus Tospovirus, type member Tomato spotted
wilt virus (TSWV)
The ORFs of the M and S RNAs are expressed by subgenomic
mRNAs.
Expression strategy includes tripartite genomic organization,
cap snatching, negative/ambisense coding, subgenomic mRNAs,
and proteolytic processing.
31. Circular ssDNA Family Geminiviridae
Genus Begomovirus Tomato yellow leaf curl virus
V2 movement
V1 coat protein
C1 replication
C2 suppression of host
C3 replication enhancement
C4 pathogenicity IR origin of replication
2700 nts
34. Conventional Approaches for the control of plant
viruses
•Breeding for resistance to plant viruses and virus vectors
•Control of plant viruses by cross-protection
Control of Vectors
•Insecticides
Exclusion of Plant Viruses
•Quarantine and certification
•Avoidance of plant viruses through cultural practices
•Certification for plant viruses
•Seed, root stocks, fruit tree propagative material
Elimination
•Heat treatment, meristem tip culture, and tip micrografting
35. Molecular Approaches for the control of plant
viruses
Pathogen-derived resistance - gene silencing
36. RNA silencing acts as a natural defense mechanism
against invasive nucleic acids, including viruses,
transposons and perhaps other highly repetitive
genomic sequences.
RNA silencing also plays a pivotal role in plant and
animal development by providing an elegant system of
gene control that can occur through RNA degradation,
translational inhibition or chromatin modification.
Post-transcriptional gene silencing
42. Yehezkel Antignus . 2000. Manipulation of wavelength-dependent
behaviour of insects: an IPM tool to impede insects and restrict epidemics
of insect-borne viruses. Virus Research 71 (2000) 213–220
An article in “Discover” Magazine January 2000 describes how
ultraviolet absorbing film over greenhouses can protect against
insect-borne viruses.