Biotic Stress – viruses
Modes of virus resistances
Viral coat protein mediated
Non structural protein
Coat protein mediated cross
Ability of first virus to prevent the effect of
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 .
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
Non structural protein mediated
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.
Tobacco, potato, tomato, soybean, rice, citrus
, orange, maize – CP TMV, AMV and TRV.
Milton Zaitlin’s lab, cornell University
, Golemboski et al, 1990 – gene of viral
Use tobacco – 3 terminal TMV 54 kDa
used for encoding repilcase.
MacFarlene and Davies (1992) similar
Not clear mechanism – not effective.
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.
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
Ribozymes are small RNA molecules –
catalytic cleavage of target RNA
Block the replication of RNA.
But not effective .
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
Malyashenko et al (1993) – has cDNA
thermal mutant MP of TMV showed
resistances at 33̇͘ but not at 24˚c.
Small RNA molecules that are unable to
multiple in host cell without helper virus.
Not in replication but affect diseases
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
Mechanism of post-transcriptional gene silencing (PTGS)
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
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!!!