This document discusses various mechanisms of viral resistance in plants, including coat protein-mediated resistance, non-structural protein resistance, antisense RNAs, ribozymes, movement proteins, and satellite sequences. It provides details on experiments demonstrating coat protein-mediated cross protection using tobacco mosaic virus sequences. Non-structural or replicase proteins from viruses like tobacco mosaic virus have also been used to generate resistant plants but the mechanisms are not clear. Antisense RNAs work by hybridizing with and blocking mRNA from the target gene. Ribozymes and satellite sequences have also been explored as resistance mechanisms but were not very effective. Gene silencing is another potential mechanism of viral resistance in transgenic plants.

1. Viral resistance

2. STRESS
Abiotic Component
Biotic Component
Sunlight
 Salt concentration
 Drought conditions
 Temperatures
 Soil condition
 Oxidative agents
 Cold conditions
 Metal toxicity


Virus
 Fungal pathogens
 Bacteria
 Nematodes
 Insects
 Weed
 Parasitic angiosperms

3. INFECTED LEAF
Biotic Stress – viruses
 Modes of virus resistances
 Viral coat protein mediated
 Antisense
 Ribozymes
 Satellite sequences
 Non structural protein
resistance
 Gene silencing


4. Coat protein mediated cross
protection
Ability of first virus to prevent the effect of
second virus.
 Sanford and Johnston (1985)
 Powell – Abel et al.(1986)
 Part of viral genome
 Focused on codes of coat protein of TMV
 Well studied + easily transformed by
Agrobacterium tumefaciens .


5. Cont…..
 CP
coding seq
Engineered CP coding seq
cassette vector (pMON316)
* 35 CaMV promoter
* NOS terminator signal
 In agrobacterial cells
 Tobacco leaf disc – kanamycin medium
 Plant with TMV
Notes:- 3:1 ratio, increased infection = late
symptoms

6. Non structural protein mediated
resistances
Non structural “replicase” protein
 54 kDa ORF of TMV – Golemboski et al. (1990)
 Pinto et al. (1999) oped rice yellow mosaic virus
resistant transgenic crop by replicase.
 Eg.
Tobacco, potato, tomato, soybean, rice, citrus
, orange, maize – CP TMV, AMV and TRV.


7. Cont…..
Milton Zaitlin’s lab, cornell University
, Golemboski et al, 1990 – gene of viral
replicase.
 Use tobacco – 3 terminal TMV 54 kDa
used for encoding repilcase.
 MacFarlene and Davies (1992) similar
expt.
 Not clear mechanism – not effective.


8. Antisense RNAs
A Complementary DNA strand of a gene can
be inserted in reverse orientation this is
referred as antisense gene.
 mRNA by normal gene complementary to
mRNA of antisense gene.
 Hybridize
 Block the specific gene expression.
 Sanford and Johnston (1985).
 Eg. Beta 1,3-glucanase was down regulated
by antisense RNA in Tobacco + tolerance
mosaic virus+ delayed spread+ reduced virus
yield.


9. Ribozymes
Ribozymes are small RNA molecules –
catalytic cleavage of target RNA
 Block the replication of RNA.
 But not effective .


10. Movement proteins
rapid spread of virus.
 30kDa protein of TMV
 32 kDa protein of brome mosaic virus
 transgenic tobacco plant – mutated
30kDa of MP.
 hence competes with TMV virus
 Develop resistance
 Malyashenko et al (1993) – has cDNA
thermal mutant MP of TMV showed
resistances at 33̇͘ but not at 24˚c.
˚c


11. Satellite sequences

Small RNA molecules that are unable to
multiple in host cell without helper virus.
 Not in replication but affect diseases
symptoms
 cucumber mosaic virus cucumovirus (CMV)
symptoms – reduced – carrying satellite
 Transgenic tobacco and tomato plant with
CMV satellites – china – (1990 - 1992)
 not good- sever disease symptoms
 Satellites mutates very fast
 Recombination bt satellites – serious

12. Mechanism of post-transcriptional gene silencing (PTGS)

13. Gene silencing in transgenic plants
It was firstly reported when introduction of
additional chalcone synthase gene was
transformed to petunia flower to intensify the
voilet color of flower
 Obtained flowers (transgenic lines) were both
1. intensed violet colered type- transgenesis
worked
2. and white colored as well-Both native and
transgenic chalcone synthase turned off
 Stable integration and expression of transgene
is required for commercial exploitation.
 Expression of introduced gene can be abberant
- GENE SILENCING!!!


14. bhendi yellow vein mosaic virus – gene silening in
varoius plant

15. References
H.S Chawla, Introduction to plant
Biotechnology(2002) oxford and IBH
publishing co. pvt ltd.
 U. Satayanaryana, Book of Biotechnology
(2010) 6th ,Uppala author-publish interlinks.
John barton, transgenic plants
(1992), imperial college press.
A.Slater, N.Scott and M.Fowler, Plant
biotechnology (2003),oxford university
press.
Google images.


16. THANK
YOU