Genetically engineered resistance-virus gene derived resistance.pdf

Genetically engineered resistance-virus gene derived resistance

1. Genetically engineered resistance:
Virus/pathogen derived resistance
Lecture: 16

3. Plant Pathogenic Virus
RNA virus DNA virus
Plant pathogenic viruses -450 species
dsRNA
ssRNA(-)
ssRNA(RT)
ssRNA(+)
ssDNA
dsDNA

4. crops
Plant virus and shape

6. Geminivirus
Geminivirus disease complex
Whitefly Plant

8. Transgenic strategies
1.Pathogen-derived resistance through the expression of viral
proteins
Replication associated protein
Coat protein-mediated protection
Movement protein
Satellite RNAs
Defective-interfering viral nucleic acids
2.Pathogen-derived resistance without protein expression
Gene silencing
Antisense RNA
3.Resistance due to the expression of non-pathogen derived
antiviral agents
Virus-induced cell death
DNA binding protein
GroEL-mediated protection
Peptide aptamers
InPAct

9. Pathogen derived resistance
PDR is the first and main antiviral transgenic approach used
Pathogen sequences are deliberately engineered into the host
plant genomes
Cross-protection forms the basis of PDR ie., the presence of
pathogen sequence may directly interfere with the replication
of the pathogen or may induce some host defense mechanism.

10. Pathogen-derived resistance through the
expression of viral proteins
Replicationassociated protein (Reps)
•Viral gene transcrioption regulation
•Initiation & termination of viral replication
•Regulation of host gene expression
Eg. Interaction of geminiviral Rep with host pRBR induce viral
DNA synthesis
•Driving cells into “S” phase
•Activating the expression of “S” phase specific factors

11. Pathogen-derived resistance through the
expression of viral proteins
Coat protein-mediated resistance
•Systemic infection by monopartitegeminiviruses(Rojas et al., 2001)
•TomatoplantsexpressingCPofthemonopartitebegomovirus(TYLCV)
exhibiteddelayedsymptomDevelopment
•CP of bipartite geminivirusesis not absolutely necessary , as NSP can
substitute (Poomaet al., 1996)
•CP-mediated strategy against bipartite geminiviruseswill not produce
a high level of resistance

14. Pathogen-derived resistance through the
expression of viral proteins
Movement protein (MP) -mediated resistance
•Cell-to-cell and long distance systemic spread
•Usedtoengineerresistancetovariousbegomoviruses
•Transgenic plants expressing the defective movement protein were
resistant to both ToMoV & CaLCuV
(Shepherd et al., 2009)

16. Antisense and Ribozymes
constructs have been designed that express a negative sense
RNA molecule that will hybridize with the infecting virus
sequence.
Ribozymesare catalytic RNA molecules capable of catalyzing
the cleavage of the target sense RNA sequence.
The aim is to block replication by the formation of a double
stranded RNA:RNA hybrid and to cut a key region of the virus
genome before it is able to replicate.

17. Pathogen-derived resistance without protein
expression
Gene silencing -mediated resistance

18. Pathogen-derived resistance without protein
expression
Antisense RNA -mediated resistance