Caulimovirus and Tungro virus

1. Genome structure of
caulimovirus and rice tungro
virus
Presented By
Surabhi ps
2nd Msc biology

2. CAULIFLOWER MOSAIC VIRUS(CaMV)
• The CaMV causes mosaic disease in cauliflower.
• CaMV is prototype of caulimovirus group.
• First known virus of higher plants with DNA as its genetic material.
• Used in plant genetic engineering as prominent vector.
• Also called cabbage mosaic virus or cabbage virus –B.
HOST RANGE- Restricted to members of Brassicaceae(Cruciferae)
• Cause vein clearing or banding Mosaic in Arabidopsis, Brassica sps.,
Raphanus sps.

3. STRUCTURE
• CaMV is an icosahedral virus.
• Diameter -50nm
• Molecular weight -23×10^6 dalton.
• Spherical virus.
• The genome of this virus consistsof dsDNA.
• Capsid is multilayered.
• CaMV contains 35%nucleic acid and 65%protein.
• DNA is present between the 2nd and 3rd layer of capsid.
• The arrangement of capsomers in the capsid is not clear.
• Virion has two major protein and two minor proteins.

4. Genome of CaMV
• Circular dsDNA.
• Size 8kbp
• Two strands.
1.(+)strand –beta strand
2.(-) strand-alpha strand
• (-) strand –single discontinuity or gap
• (+ )strand- two gaps.
• Gaps are primer binding sites for replication.
• At the gaps, one end is slightly overlapping the other.
• The overhangs are 8-20 nucleotide long.
• Closely packed gene- open reading frames(ORFs).
• Small intergenic sequence – lS

5. • ORF1- codes for factors required for cell to cell spreading of virus
particles.
• ORF2- responsible for aphid mediated transmission of the virus.
• ORF3 and ORF4- encodes for structural protein of virus capsid.
• ORF5- code for viral reverse transcriptase.
• ORF6- codes for proteins of viroplasm that take’s part in induction of
disease symptoms.
• ORF7-may involve in DNA binding activity.
• IS – occurs between ORF7 and ORF6.

6. Replication of CaMV
CaMV transmitted to plants mainly by aphids.After entry uncoating and
release of CaMV DNA occur within the cytoplasm.
• Viral DNA transported to the cell nucleus.
• Removal of overhangs by host encoded DNAse and closing of gaps by host
encoded DNA ligase.
• Viral DNA becomes associated with histone proteins of the host cell to
form minichromosome configuration.
• Two RNA transcript are generated as result of transcription and
transported to the cytoplasm of host cell.
• 35S RNA codes for Structural protein.
• 19S RNA is involved in replication of genome

7. • ds DNA virus is synthesized from RNAs by the enzyme reverse
transcriptase.
• Host RNA act as a primer for synthesis of viral DNA.
• Encapsidation Occurs in the cytoplasm to form progeny virion.
• Newly formed virus particles aggregate together to form inclusion
bodies in the cytoplasm, regulated by the gene 2 and 6.
• Mature virions escape from the Infected cell and infect new cells.
• As a result of replication, disease symptom appear in the host.

9. BADNA VIRUS
Rice tungro virus disease
• Its one of the most damaging and destructive of rice in south east
Asia and also in southern parts of china.
• Tungro is the result of concurrent infection by two viruses.
1. ssRNA virus –Rice tungro spherical virus (RTSV)
2. dsDNA virus- Rice tungro bacillus virus (RTBV)

10. RICE TUNGRO BACILLIFORM VIRUS (RTBV)
• Member of the genus tungrovirus.
• Along with members of the genus Badnavirus.
• RTBV is readily distinguished from other genera in the Caulimoviridae by its
bacilliform-shaped virions.
• The genome organization of RTBV is very similar to that of the genus Badnavirus,
it differs by the presence of a fourth ORF (ORF4).
• RTBV is a pararetrovirus belonging to a monospecific genus, Tungrovirus, in the
family Caulimoviridae.
• It has bacilliform particles of about 130 nm length (though there can be longer
ones in some isolates) and 30 nm diameter .
• Structure is based on a T = 3 icosahedron cut across its threefold axes, the tubular
portion being made up of rings of hexamer subunits with a repeat distance of
about 10 nm.

11. • The particles contain a circular double-stranded DNA genome of about 8
kbp which has one discontinuity at a specific position in each strand.
• The genomes of several isolates have been sequenced and the virus has
been shown to have four open reading frames (ORFs), all on one strand.
• ORF code for protein more than 10kDa.
• First three ORF closely packed and interfaces with the sequence ATGA
• ATG-start codon of the downstream ORF
• TGA- stop codon of upstream ORF.
• ORF4 separated from ORF3 by short non coding region.
• ORF1 is separated from ORF4 by longer non coding region.

12. • The genome is transcribed asymmetrically to give a more-than-genome-length RNA,
which is the template for reverse transcription and is also the templatefor the translationof the
first three ORFs.
• The fourth ORF is translatedfrom an mRNA spliced from the more-than-genome-length
transcript .
• The doublecomplete circles represent the dsDNA genome, the positionsof the
discontinuities(D1 and D2) being shown.

13. • In this Picture the genome of RTBV.
• Inner genome with the position of the discontinues D1 and D2
• Arcs show the position of the 4 open reading frame (ORF).
• ORF1 shaded lighteras it does not haveconvenitalAUG start codon.
• The positionof the sequence motif for coat protein (CP), RNA bindingRNAse H(RH), aspartateprotease
(PR), reverse transcriptase (RT),RNA binding‘cys’ sequence(RB), on ORF3 polyprotein areindicated.
• Outer circle 35s RNA with terminal redundancy,the spot being the 5’ end and arrow head 3’ end.

14. Thank you!