Virus replication requires several components including polymerases, transcription, mRNA, tRNA, translation, and ribosomes. Viruses enter plant cells through wounds or vectors and shed their capsids. For single-stranded RNA viruses, the naked RNA induces the cell to form a viral RNA polymerase that copies the viral RNA into complementary RNA. This cRNA then serves as a template to produce more viral RNA and mRNA for protein subunit production using the host's amino acids, tRNA, and ribosomes. The assembled nucleic acids and proteins then form new virus particles (virions) that exit the cell.

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

2. COMPONANTS FOR VIRUS SYNTHESIS
• A polymerase is an enzyme that synthesizes long chains of polymers or
nucleic acids. DNA polymerase and RNA polymerase are used to
assemble DNA and RNA molecule
• Transcription is the process by which the information in a strand of
DNA is copied into new molecule of messenger RNA (mRNA). DNA
safely and stably stores genetic material in the nuclei of the cells as a
reference or template

3. • Messenger RNA (mRNA) carries the genetic
information copied from DNA in the form of a series
of three base code “words” each of which specifies a
particular amino acid

4. • Transfer ribonucleic acid (tRNA) is a type of RNA molecule that
helps decode a messenger RNA (mRNA) sequence into protein.
• tRNA functions at specific sites in the ribosome during translation
which is process that synthesizes a protein from an mRNA molecule.

5. • Translation is the process by which a protein is synthesized from
the information contained in a molecule of messenger RNA
(mRNA)
• Translation occurs in structure called the ribosome which is factory
for the synthesis of proteins

6. Virus infection and replication
• Virus enters into the plant cell through wounds made
mechanically or by vector or naturally by deposition into an ovule
by an infected pollen grain
• Once the virus enters inside the host it becomes naked by
shedding its capsid or coat
• In case of ss-RNA virus the naked RNA inside the host cell
induce the cell to form the viral RNA polymerase.
• This RNA polymerase utilizes the viral RNA strands as a
template and forms complementary RNA (c-RNA)

7. Virus infection and replication
• The complementary RNA soon get separated from the original
RNA strand and serve as template for the synthesis of more viral
RNA strand.
• These synthesized new viral strand or segment of this act as
messenger RNA (m-RNA) for the production of protein subunits.
• For this process, virus utilizes the amino acids, ribosomes and
tRNA of the host for the synthesis of its protein subunits
• When the nucleic acid and virus protein subunits have been
produced the nucleic acid organizes the protein subunits around it
assembled together and form the complete virus particle namely
virions

8. • In case of RNA viruses (ss-RNA or ds-RNA) the entire process
takes place in the cytoplasm of plant cell itself
• In ssDNA virus the virions are formed in the nucleus and then
release into the cytoplasm of host cell. The first intact appear
virions appear in plant cell approximately 10 hrs after
inoculation. The multiplied virus particle exists with in the host
cell as inclusion bodies

9. ds-DNA virus replication
• First viral ds-DNA enter into the cell nucleus and where it
becomes twisted and supercoiled to form a mini chromosome
• This mini chromosome like double stranded viral DNA is the
transcribed into two single stranded RNA’s and transported into
the cytoplasm
• Where one small strand become translated into virus coat
protein and other large RNA strand become encapsidated by
coat protein subunits and is used as a template for the reverse
transcriptase into a complete virion ds-DNA

10. ds-DNA virus replication

11. • In some single strand negative RNA(-ssRNA)
• The freed from the protein coat must be first transcribed into a
positive strand RNA by a virus carried enzyme called
transcriptase and then the remaining process of replication takes
place