introduction What is virus What is virus resistance plant History Gene use for develop virus resistance plant Coat protein gene cDNA of satellite RNA Defective viral genome Antisense RNA approach and Ribozyme – mediated protection conclusion References

1. Virus resistance plant
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. synopsis
introduction
What is virus
What is virus resistance plant
History
Gene use for develop virus resistance plant
•Coat protein gene
•cDNA of satellite RNA
•Defective viral genome
•Antisense RNA approach and
•Ribozyme – mediated protection
conclusion
References

3. Introduction
As in many years of the past, plant viruses are still
forming a major problem in the cultivation of many
vegetable and ornamental crops throughout the
world. For long times, these pathogens have been
controlled using conventional measures like crop
rotation and other cultivation techniques. Genetic
resistance to plant viruses has been used for control
agricultural losses to viral diseases

4. •What is virus
A virus is a small infectious agent that can replicate only inside
the living cells of organisms. It is a unique bridge between living
and non-living things. Viruses infect all types of organisms, from
animals and plants to bacteria and archaea
•What is virus resistance plant
Transgenic plants contain a gene that has been artificially inserted
into it. The gene sequence that is inserted into it, know as the
transgene, can come from an unrelated plant or even from a
complete different species. In virus resistance transgenic plant the
gene which inserted into plant is derived from the pathogenic
viruses and this type of plants show resistance again pathogenic
viruses, Another term for transgenic plants is a genetically
modified crop, or a GM crop.

5. •History
first virus-resistant transgenic plant (ZW 20
squash developed by Asgrow Seed Company) was
approved by the U.S. Department of Agriculture
(USDA) in 1983.
Powell Abel et al. (1986) showed that transgenic
plants expressing the CP of tobacco mosaic
tobamovirus (TMV) imparted resistance to TMV.

6. •Virus resistance
Several approaches have been used to engineered plants for
virus resistance which are as follows:
•Coat protein gene
•cDNA of satellite RNA
•Defective viral genome
•Antisense RNA approach and
•Ribozyme – mediated protection
All these strategies are based on genes derived from the
pathogenic viruses themeselves. The disease resistance gene
generated by employing pathogen genes is called pathogen –
derived resistance (PDR). PRD has been realized in the cases
of bacterial and fungal diseasea as well.

7. •Viral coat protein-mediated protection
The use of viral CP as a transgene for producing virus resistant plants is
one of the most spectacular successes achieved in plant biotechnology.
When transgenic plants express the gene for a coat protein of a virus that
normally infects those plants, the ability of virus to subsequently infect the
plants and spread systemically is often greatly diminished. Although the
precise mechanism by which the presence of coat protein genes inhibits
viral proliferation is not understood,
it is clear that the antiviral effect occurs early in the viral replication cycle
and, as a result, prevents any significant amount of viral synthesis, this
feature is an advantage because it decreases the probability of selecting for
spontaneous viral mutants that can overcome this resistance and replicate in
the presence of virus coat protein. The viral coat protein gene approach has
been used to confer tolerance to a number of different plant viruses with
this approach, researchers have developed virus-resistance transgenic plant
for a number of different crops. Although complete protection is not usually
achieved, high level of virus resistance have been reported. Moreover, a
coat protein gene from one virus some times provides tolerance to a broad
spectrum of unrelated viruses.

8. the first transgenic plant of this type was tobacco
produced in 1986. It contained the coat protein
gene of tobacco mosaic virus (TMV) strain U1, ). it
showed reduced disease symptoms when
infected with (TMV) symptoms either failed to
develop or were considerably delayed.
•Virus coat protein gene
Transgenic plants having virus coat protein gene
linked to a strong promoter have been produced
in many crop plants. e.g., tobacco, tomato,
alfalfa, sugarbeet, potato, etc.

9. •cDNA of satellite RNA
some RNA viruses have small RNA molecules, called satellites,
which depend on the viral genomes for their replication, but are not
necessary for viral functions. In many cases. Satellites either
increase or decrease the severity of disease produced by the virus
carrying it. The cDNA copies of satellites that reduce disease
severity have been integrated into host genome, expression of the
satellites has been shown to reduce disease symptoms as well as
virus accumulation under both greenhouse and field conditions.
For example, tobacco plants expressing the satellites of cucumber
mosaic virus (CMV) showed reduced disease symptoms when
infected with CMV or with the related tomato aspermy virus
(TAV).

10. •Antisense RNAApproach
Antisense RNA, in its simplest form, can be produced by
inverting a cDNA copy of an mRNA with respect to the
promoter in an expression vector; this yields a full-length
complementary copy of the mRNA sequence. Fragments
smaller than full-length can also be effective.
Antisence RNAmolecules are thought to interact with
mRNA molecules by base-pairing to form double stranded
RNA. Transgenic tobacco plants expressing antisence RNA
of the CMV coat protein gene showed reduced virus
accumulation, and prevention of systemic spread at low
concentrations of CMV inoculum.
But this approach was much less effective than coat protein-
mediated resistance. In contrast, expression in tobacco plants
of an antisense RNA of a TMV coat protein gene segment
was totally ineffective against infection with TMV. Clearly,
this approach has not been very successful so far.

11. AAAAA(A)n
5’ 3’
3’ 5’
VPg or
CAP
Antisense RNA
Target virus RNA
Antisense RNA
Antisense RNA hybridizes with target virus
RNA to interfere with virus replication or to
block virus replication

12. •Ribozyme-mediated protection
Another approach to engineer plants for virus resistance is based on ribozymes.
Ribozymes are RNA molecules that exhibit enzyme activities.The ribozymes used
to generate virus resistance are,in fact, hybrid RNA molecules consisting of
tobacco ringspot virus (TobRV) satellite RNA endoribonuclease catalytic
sequences linked to the antisence RNA of specific genes against which they are
targetted. The strategy consists of (i) producing a ribozyme specific to a part of the
target virus genome, (ii) to produce cDNA of this ribozyme and (iii)to integrate it
into the host plant genome.
Transgenic tobacco plants expressing ribozymes against TMV showed some
resistance to TMV infection.Ribozymes may be useful in producing resistance to
several viruses within a group where conserved sequences exist.Rnase P linked
with external guide sequences is a potential alternative to ribozymes.

13. Ribozyme
Ribozyme cleaves the target virus RNA sequence at a specific
target region to block virus replication
AAAAA(A)n
5’ 3’
3’ 5’
AAAAA(A)nOH
P 5’3’
Vego or
CAP

14. Plant virus diseases cause severe constraints on
the productivity of a wide range of
economically important crops worldwide
There are difference techniques used to produce
virus resistance transgenic plants
A number of strategies have been used to control
plant virus disease with the expression of different
viral sequences, The resistance conferred by these
methods is generally against one specific virus or
closely related viruses.
conclusion

15. References
Text book of plant biotechnology---B.D.Singh
Plant biotechnology-------U.Satyanarayan
www.ncbi.nim.gov
www.ag.auburn.edu
www.accessexcellence.com
www.fao.org
www.ifse.tamu.edu