Virus resistant transgenic plants

virus resistant transgenic plants

1. virology Virus Resistant Transgenic Plants

2. {Tulip breaking virus (TBV)} (https://burleytobaccoextension.ca.uky.edu/content/tobacco-mosaic-virus-tmv) (https://en.wikipedia.org/wiki/Tulip_breaking_virus) {Tobacco mosaic virus (TMV) symptoms on tobacco leaf}   Martinus Beijerinck Contagium vivum fluidum “Contagious living fluid"  Plant viruses

3. Control of plant viruses There are several strategies that one can use to prevent and control viral infections: Use certified seed or plants, which have been tested for known pathogens. Control weeds around the fields as weeds can harbor both viruses and their vectors, serving as a source of inoculum for the field. Use seed treatments and/or spraying insecticides on the crop. Since most plant viruses are transmitted by arthropod vectors, this can be an effective strategy but it does not work in cases where the viruses are transmitted quickly. Once a virus is in a field, farmers can take action by removing infected plants followed by destroying them). This can be a costly measure and is used in cases where the type of virus can be transmitted quickly.

4. Aphids Whiteflies Leafhopper Beetles Entry of Virus in the plant {The types of virus transmission} (https://www.biofortified.org/2017/07/how-virus-resistance-works-gmos/)

5. Plant responses to the viral infection Dominant resistance (R) genes {Dominant virus resistant genes} Maule, A. J., Caranta , C., & Boulton , M. I. (2007). Sources of natural resistance to plant viruses: status and prospects. Molecular plant pathology, 8(2), 223-231.

6. Recessive resistance (r) genes {Recessive virus resistant genes} Maule, A. J., Caranta , C., & Boulton , M. I. (2007). Sources of natural resistance to plant viruses: status and prospects. Molecular plant pathology, 8(2), 223-231.

7. {Basic organization of plant virus genome (TMV)} (https://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx) +ve sense mRNA leaky stop codon

8. -ve sense RNA template +ve sense viral RNA Allow movement to adjacent cell For encapsidation to form new TMV virus {Replication cycle of TMV} (https://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx)

9. Virus resistance transgenic plants Protein mediated resistance 1.1 Coat proteins mediated resistance {Non transgenic infected cell} (Kahn, A. Transgenic Plants in Agriculture: Ten Years Experience of the French Biomolecular Engineering Commission)

10. {Transgene expressing a coat protein} {Transgene expressing a coat protein but no non structural proteins} (Kahn, A. (1999) Transgenic Plants in Agriculture: Ten Years Experience of the French Biomolecular Engineering Commission, ISBN2742002014, 9782742002016) Coat protein in transgenic plants can be used to enhance the production of movement proteins and coordinate the formation and size of virus replication complexes thereby limiting the spread of cell-to-cell infection.

11. 1.2 Replicases mediated resistance This type of protection is otherwise known as non-structural mediated resistance. In the genomic organisation of TMV replicase enzyme is probably responsible for the synthesis of genomic and subs genomic RNA’s. Presence of 54 kDa gene in transgenic tobacco precludes disease symptoms in the plant. According to one hypothesis 54 kDa proteins is a component of the membrane replicase . This 54 kDa protein non-structural proteins contains a Gly -Asp-Asp motif conserved sequence probably interfere with TMV replication by binding to viral proteins that regulate replication or gene expression.

12. 1.3 Movement proteins mediated resistance {Cell to cell movement in TMV} (https://www.apsnet.org/edcenter/intropp/lessons/viruses/Pages/TobaccoMosaic.aspx) As movement protein is non-structural viral protein known to function in viral movement. Accumulation of 32 kD movement protein in transgenic tobacco have been shown to reduces the amount of tobacco mosaic virus after infection by can competing with native movement protein of virus and reduces its movement.

13. Gene silencing mediated resistance RNA Interference ( RNAi ) Key proteins involved in RNA interference or silencing are Dicer like proteins (DCL) Argonaute proteins (AGO) RNA dependent RNA polymerases ( RdRp ) HEN1 and HYN1 Pathways observed in RNA silencing Cytoplasmic siRNA silencing The silencing of endogenous mRNAs by miRNAs   Pathway associated with DNA methylation and the suppression of transcription 

14. Antisense RNA mediated protection Small fragments of antisense RNA RdRp Viral cDNA Transgene Cis acting elements Homologous viral RNA {Mechanism of antisense RNA dependent resistance} ( Baulcombe D. Mechanisms of Pathogen-Derived Resistance to Viruses in Transgenic Plants. The Plant Cell. 1996;8(10):1833-1844.)

15. Satellite RNA Mediated Resistance The ability of some satellite RNA to attenuate the symptoms of their helper virus has been established. Satellite RNAs are species of RNA associated with certain plant RNA virus. The satellite RNA always depends on the virus for its replication and transmission and their nucleotide sequence seems to be unrelated to that of the viral genome. The resistance can be compromising in one of the abilities of attenuating sat RNA to prevent helper virus coat protein from entering chloroplast of infected cells.

16. Plantibody Mediated Resistance By the production of monoclonal antibodies in plants expressing a appropriate IgG fab 2 fragment or single chain Fv antibody for possibility of providing protection against viral and other diseases. It may be very effective to use monoclonal antibody targeted against catalytic (non-structural) viral proteins when the antigen concentrations are less and interfere virus replication. Ribozyme Mediated Resistance Ribozymes , commonly known as catalytic RNA, are small RNA molecule. Ribozymes normally cleaves spe­cific target RNA ( introns ) intramolecularly . However, the catalytic domain cleaves before GUC triplet codon . The efficiency of RNA cleavage depends on its kinetics.

17. Virus-derived transgenic products in the market {Virus Resistant Papaya} (https://www.biofortified.org/2017/07/how-virus-resistance-works-gmos/) There are several viral diseases that cause food insecurity and/or severe economic losses that have transgenic solutions. The most widely known transgenic on the market is Papaya that is resistant to PRSV (papaya ringspot virus). At the time, the papaya industry was in risk of being completely wiped out due to PRSV and all other attempts had failed. Insecticides made the problems worse as the virus is quickly transmitted (in seconds). The GE papaya saved the industry.

18. (https://www.biofortified.org/2017/07/how-virus-resistance-works-gmos/)

19. Risks associated with protein mediated resistance Recombination   The potential for environmental impacts arising as a result of genetic exchange between naturally occurring plant viruses and virus-derived sequences. This is because there is a finite probability that virus-virus recombination and virus- transgene recombination could give rise to a new ( chimeric ) virus capable of spreading as a virulent disease. Heterologous Encapsidation It occurs when closely related viruses use the functional viral CPs expressed in transgenic plant cells. A possible alteration in the process of transmission and host specificity that can contribute to infection. Complementation It occurs in transgenic plants if the transgenically expressed protein complements a mutant virus, which is defective in one or more genes.

20. Conclusion Virus-derived transgenic resistance holds great promise in sparing growers and consumers the costs of losses due to virus infection. Furthermore, this technology has saved at least one crop, papaya grown in Hawaii, and holds the potential to grant those in developing nations food security by preventing losses in staple crops. Some of the other benefits of this approach to controlling plant viruses is that it reduces sprays that were used to control the arthropod vectors, while not altering how the crops are grown. One of the main challenges is that resistance to one strain of virus may not give strong resistance to other strains, so the evolution of new virus strains must be closely monitored.

21. Thank you