Viral infections in plants can be controlled through several strategies including using certified seed/plants, controlling weeds that harbor viruses, and insecticide use since most viruses are vector-borne. Transgenic virus resistance involves expressing viral genes including coat proteins, replicases, movement proteins, or antisense RNA to interfere with viral replication or movement. The papaya industry was saved through a transgenic papaya resistant to papaya ringspot virus. While virus resistance holds promise, risks like recombination or heterologous encapsidation must be monitored.

2. {Tulip breaking virus (TBV)}
(https://burleytobaccoextension.ca.uky.edu/cont
ent/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
1. 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. 2. 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
1. 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/TobaccoMosa
ic.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. 2. 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 fab2fragment 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.