Virus resistance plant, production

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 RNA Approach 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)n OH 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