Virus infection and replication

Detailed explanation on Virus infection and replication

1. Virus infection and
replication
N. H. SHANKAR REDDY
Ph.D., Plant Pathology
AnnamalaiUniversity

2. 1. Attachment
•The virus attaches to the host cells

3. 2. Penetration (entry into the host cells)
Virusesenterintothehostcellsthroughwoundsormechanicalinjuriescreatedby
vectorsorbyotherfactors
Mostoftheplantvirusesenterintotheplantcellsthroughinsectdamagesduringfeeding
Mode of entry of plant viruses
Mode of entry Virus name
Mechanicalwounds TMV,PVX,BCMV
Woundsmadebyvectors PLRV,WTV,TLRL
Seeds or vegetative
propagation
CMV,BCMV,Peastripevirus

4. 3. Uncoating of viral genome
Allvirusesareencapsulatedbyprotein
coatwhichprovidesprotectiontothe
nucleicacidwhichispackedinside.
Onceplantvirusentersintothehostcell,
itstartstoshreditscapsid/coatprotein
toreleasenucleicacidintocytoplasm
forreplicationprocess.
Theabilityofuncoatingdependsupon
structureofviruscoatprotein.

5. 4. Synthesis
i.Transcription (production of mRNA)
IftheviralgenomeissinglestrandedRNA(ssRNA),thenakedRNAinduces
hostcelltoproduceRNApolymerase.
ThetranscriptionofmRNAfromDNAvirusesinvolveshostDNAdependent
RNApolymeraseoperatingonadoublestrandedDNA.

6. ii. Translation of mRNA into proteins
ThesynthesizedviralRNAservesasmessengerRNA(mRNA),
immediatelybindswithribosomeandforcestoproducevirusspecific
proteinsubunits.
Thevirusesutilisehostcellmachinery(aminoacids,ribosomes,
ribosomesandtRNAofhost)fortheproductionofproteinssubunits.

8. 5.Viralgenomereplicationandgene
expression
•Production of new RNA molecule identical to template RNA is called Replication.
•The protein specific viral replicating enzymes RNA polymerase (RNA dependent) is
responsible for viral replication of all (+)ssRNAviruses that encode one or more proteins.
Host cell strategies
Nucleic acid conversion Enzymes for replication
RNAtoRNA RNAdependentRNApolymerase
RNAtoDNA RNAdependentDNApolymerase
(reversetranscriptase)
HostcellDNAtoRNA DNAdependentRNApolymerase

9. 6. Production of viral genome
•Byusinghostcellmachinery,thevirusesstarttoproducemRNAforthefurtherhuge
productionofviralRNAparticles.

10. 7.Assemblyofvirions/maturationof
virions
Assemblyofnewlysynthesisedviral
componentsintocompletevirions.
Oncethenucleicacidandproteinsubunits
areproducedseparatelyinacell,they
assembledtogethertoproduceintactvirus
particlecalled“virion”.
Experimentalevidencessuggestedthatmany
viruses,especiallyRNAvirusescanbe
disassembledintotheirconstituentcoat
proteinandnucleicacidandagaincanbe
reassembledinvitro

11. 8.Locationofthegenomeproduction
IncaseofRNAviruses(ssRNAanddsRNA)theentireprocesshappensin
cytoplasmofplantcell.
IncaseofDNAviruses(ssDNAanddsDNA)entireprocesstakeplacein
nucleusandreleasedintocytoplasmofplantcell.

12. 9.Releaseandspreadofvirusesinplants
Theassembledvirusparticlesaredeparturetodifferentplantpartsusingplant
physiologicalprocess.
Therearetwoformsofspreadofviruseswithinaplant:shortdistanceandlong
distance.
Theshort-distancespreadisfromcelltocellandthe
longdistancespreadistodistantpartsoftheplant.

14. Video available at you tube
Channel –Geeky Researcher