plant virus replication, attachment, penetration, uncoating, transcription, translation, genome replication, assembly, release of virion, mRNA, tRNA, ribosome, RNA polymerase, three base code words, protein synthesis DNA dependent RNA polymerase, host cell machinery mRNA to protein

1. ANNAMALAI UNIVERSITY
FACULTY OF AGRICULTURE
DEPARTMENT OF PLANT PATHOLOGY
PAT-502 PLANT VIROLOGY
TOPIC:VIRUS REPLICATION
BY
V.AJAYDESOUZA
1ST YEAR M.Sc.,(Agri) Plant Pathology
COURSE TEACHER
A.MUTHUKUMAR
ASSOCIATE PROFESSOR
DEPARTMENT OF PLANT PATHOLOGY

2. STAGES OF VIRUS REPLICATION
ATTACHMENT OF
VIRUS
PENETRATION OF HOST
TRANSCRIPTION
TRANSLATION
ASSEMBLY
UNCOATING
RELEASE OF VIRION

3. ATTACHMENT (ADSORPTION)
• This is the first steps in virus
infection in which
interaction of virus with a
specific receptor site on the
surface of host cell occurs
• Viral protein on the capsid
or phospholipid envelope
interact with specific
receptors on the host cellular
surface. This specificity
determines the host range
(tropism) of virus

4. PENETRATION
• The virus enters the plant cell by
wounds created artificially, by
vector, or naturally when an infected
pollen grain deposits itself inside an
ovule
• The process of attachment to a
specific receptor can induce
conformational changes in viral
capsid protein or the lipid envelop
that results in fusion of viral and
cellular membranes

5. UNCOATING
• Once within the host, the virus sheds
its capsid or coat and becomes
naked.
• Uncoating is defined as release of
viral genome from capsid and is
accessible to enzyme required to
translate, transcribe and replicate it

6. TRANSCRIPTION
• The process of transcription involves copying information from a
strand of DNA into a new messenger RNA molecule (mRNA).
DNA preserves genetic material in the cells' nucleus securely and
permanently as a template or reference.
• Transcription of viral genome is usually the next step in all virus
except in those virus whose genome acts directly as mRNA (eg.
Picorna virus)

8. • RNA viruses that carry minus(-) stranded RNA first transcribe
their RNA to plus (+) stranded RNA that functions as mRNA
(transcriptase)
• The transcription is catalyzed by viral RNA polymerase released
during uncoating
• The genetic information replicated from DNA is carried by
messenger RNA (mRNA) in the form of a sequence of three base
“code words” that each designate a certain amino acid.

9. TRANSLATION
• A process by which viral mRNA is translated into viral protein, using
the host cellular machinery (amino acid, ribosomes, t-RNA of host).
• The ribosome, a structure that is a factory for the creation of proteins,
is where translation takes place.

10. • A form of RNA molecule called transfer ribonucleic acid (tRNA) aids
in the translation of a messenger RNA (mRNA) sequence into protein.
• During translation, the process by which an mRNA molecule is
converted into a protein, tRNA performs specialized roles at various
locations inside the ribosome.

11. REPLICATION OF GENOME
• Replication is the process of creating new RNA molecules that
are identical to the template RNA.
• The virus specific enzyme that replicates proteins all (+) ss-RNA
viruses that encode one or more proteins are replicated by an
enzyme called RNA polymerase (RNA dependent).
• After nucleic acid replication many copy of progeny nucleic acids
formed
• The viruses begin to synthesis mRNA utilizing host cell
machinery for the massive synthesis of viral RNA particles that
come.

13. ASSEMBLY
• Once the virus's nucleic acid and protein subunits have been
created, the virus’s nucleic acid arranges the protein subunits
around it to form virions, the entire virus particle.
• With RNA viruses (ss-RNA or ds-RNA), the entire process occurs
in the plant cell's cytoplasm.
• The virions of the ss-DNA virus are created in the nucleus and
released into the cytoplasm of the host cell.

15. RELEASE
• The mechanism of virus release vary with types of virus
• The naked viruses are generally released by cell lysis
• The enveloped viruses are released by budding through special
area of host cell membrane during which virion acquire a portion
of host cell membrane
• In some animal and plant virus host cells are not killed the virus
release through special channels
• The formed virus particles are released into various plant sections
via physiological plant processes.

18. ds-DNA VIRUS REPLICATION
• The cell nucleus is where viral ds-DNA first enters and gets
twisted and supercoiled to produce a mini chromosome.
• This double-stranded viral DNA, which resembles a mini
chromosome, is then translated into two single-stranded RNAs
and carried into the cytoplasm.
• In this process, one tiny strand is translated into the virus coat
protein, and the other big RNA strand is encapsulated by coat
protein subunits and utilized as a template for reverse
transcription to create the entire virion ds-DNA