3. Fraenkel-Conrat
1955-56
• Complete, infectious TMV
particles can be
reconstituted in vitro from
the RNA and protein
components
• RNA alone is infectious
• RNA can be
“transcapsidated” in protein
from closely related virus;
resulting virus has
properties of RNA strain
reconstitute
in vitro
Virus Aa:
RNA A
capsid a
RNA
protein
symptoms (A)
extract virus
virus Aa
inoculate plants
4. Fraenkel-Conrat – 1955-56 Transcapsidation
inoculate plants
Virus Aa:
RNA A
capsid a
RNA
protein
symptoms (A)
no
symptoms
extract virus
no virusvirus Aa
inoculate plants
Virus Bb:
RNA B
capsid b
RNA
protein
symptoms (B)
no
symptoms
extract virus
no virusvirus Bb
inoculate plants
Virus Ab:
RNA A
capsid a
RNA
protein
symptoms (A)
no
symptoms
extract virus
no virusvirus Aa
5. Bill Dougherty – 1991
• RNA was critical component in
resistance in pathogen-
mediated resistance
• All of the hallmarks that later
came to be associated with
PTGS and RNAi were first
observed with Tobacco etch
virus (TEV) (1993 Lindbo et al.,
Plant Cell 5:1749-1759)
6. Brome mosaic virus
• Relatively little studied prior to 1980
• Relatively narrow host range
• Causes no important disease
• Mechanically transmitted, probably not vectored
• Similar to Alfalfa mosaic virus and Cucumber
mosaic virus, two important plant pathogens
• Now most thoroughly understood plant virus at
RNA level
7. BMV structure
• Rigid isometric particles 27 nm
• RNA1 (3.2 kb) and RNA2 (2.9 kb)
packaged alone; RNA3 (2.1 kb) and
RNA4 (1.2 kb) packaged together
• Particle is held together primarily by
protein/RNA interactions
• With RNA, 180-subunit, T=3 particles
predominate; without RNA, 120-
subunit, T=1, particles
