VIRUS INDUCED GENE

1. COLLEGE OFAGRICULTURE, OUAT, BHUBANESWAR
PL. PATH-603
ADVANCED VIROLOGY
COURSE TEACHER :-
Dr. M.K MISHRA, Ph.D
PROFESSOR
DEPT. OF PLANT PATHOLOGY
OUAT, BBSR
SUBMITTED BY :-
UDAYENDU BARIK
Adm No. 201232201
1st yr Ph.D
DEPT. OF PLANT PATHOLOGY
OUAT, BBSR
TOPIC :- VIRUS INDUCED GENE

2. Plant viruses are biotrophic pathogens they need living tissues for their multiplication.
After entering the host they use host machinery for replication and protein synthesis.
The establishment of infection is genetically determined by the availability of host
factors necessary for virus replication and movement and by the balance between
plant defense and viral suppression of defense responses.
Host factors may have antiviral or proviral activities and regulated by genes.
Antiviral activities leads to resistance and proviral activities leads to susceptible to
virus attack.
INTRODUCTION

3. Ingress or entry of virus i.e. passage of virus through host cell wall to host occurs
mainly by vectors.
A successful or unsuccessful infection mainly decided by the genes involved in it.
After virus entry uncoating occurs and it tries to use host machinery for replication
and protein synthesis.
After the entry of virus inside the host, many genes are activated due to virus
induction and are known as virus induced gene
Virus induced genes can leads resistance or susceptible responses.
Those genes are also responsible for change in host metabolism and biochemical
and physiological changes in the host.
VIRUS INDUCED GENE

4. Virus entry
Induction of
Susceptible genes
Induction of
Resistant genes
Proviral activities
leads to successful
infection
Antiviral activities
leads unsuccessful
infection
Symptom
development
Hypersensitivity(HR)
Programmed Cell Death
LAR
SAR
Gene silencing

5. After entry into the host, the susceptible genes plays important role in providing
proviral conditions in many ways which ultimately leads to successful infection and
symptom development.
Plant viruses use cellular factors and resources to replicate and move.
Plant virus replication and movement are genetically determined by a combination of
viral and host factors coordinated in a temporal and spatial manner.
The infection process of a plant by a virus can be divided into sequential phases:
virion disassembly, viral replication complex formation, virus replication, viral RNA
translation, cell-to-cell movement, systemic movement and virion formation.
SUSCEPTIBILE GENES TO PLANT VIRUSES

6. Viral RNA Translation :- Using the BMV replication system in yeast, a genetic screen identified DED1, a general
translation initiation factor essential for cell survival, as being necessary for BMV RNA translation.
Virus Replication Complex Formation :- ER-vesicle protein 14 (ERV14) interacts with and mediates BMV localization
to the perinuclear ER , while PEX19 mediates localization of the TBSV replication proteins to the peroxisome.
Accumulation or Activity of the Replication Proteins:- A cytoplasmic protein related to core RNA splicing factors,
LSM1, is required for efficient selection of BMV RNA templates for replication.
CASE STUDY

7. Virus Movement :- Virus-encoded movement proteins modify the plasmodesmata central cavity or form tubules inside
the plasmodesmata. The CaMV MP forms tubules that pass through modified plasmodesmata and transport virions
through the lumen.
Gene Silencing Suppression :- In Nicotiana benthamiana, the calmodulin-like protein (Nbrgs-CaM) is an endogenous
plant regulator of gene silencing that functions by repressing expression of RDR6. RDR6 and SGS3 participate in the
biogenesis of secondary siRNAs necessary to amplify endogenous and antiviral gene-silencing signals against RNA
viruses and Gemini viruses.
Infection of N. benthamiana by tomato yellow leaf curl China virus (TYLCCNV, a Geminivirus) and the associated βC1
DNA satellite induces expression of Nbrgs-CaM that in turn downregulates RDR6 expression, thus reducing antiviral
defence mediated by gene silencing.

8. HOST FACTORS THAT CONDITION SUSCEPTIBILITY TO PLANT VIRUSES

9. RESISTANCE GENE AGAINST PLANT VIRUSES
Resistance genes (R- gene) are genes in plant genomes that convey plant disease resistance against pathogens by
producing R proteins.
The multiplication of TMV in tomato plants is inhibited by the presence of the Tm-1 gene
Extreme resistance to PVX in potato is provided by the Rxl and Rx2 genes, which are located on chromosomes XII and V,
respectively.
HR induced by N-gene in tobacco due to TMV infection.

10. R-GENES AGAINST PLANT VIRAL PATHOGENS

11.  The regulation of gene expression in a cell to prevent the expression of a certain gene is known as gene
silencing.
 Gene silencing is often considered the same as gene knockdown.
 Gene silencing can occur during either transcription or translation and is often used in research.
GENE SILENCING
Types of gene silencing
TRANSCRIPTIONAL
• Genomic Imprinting
• Paramutation
• Transposon silencing
(or Histone Modifications)
• Transgene silencing
• Position effect
• RNA-directed DNAmethylation
POST-TRANSCRIPTIONAL
• RNAinterference
• Virus induced gene
silencing
• Nonsense mediated decay
MEIOTIC
• Transvection
• Meiotic silencing of
unpaired DNA

12.  The VIGS is a technique in which viral
vectors bearing a fragment of desired genes
(non-viral insert) are used to silence that
particular gene.
It is RNA mediated antiviral post
transcriptional gene silencing defense
mechanism.
 Viral vectors carrying a target gene fragment to
produce dsRNA which trigger RNA-mediated
gene silencing
 It provides a powerful approach – genetic and
functional characterization of genes in plants.
 Virus induced gene silencing first used –
recovery from virus infection.
 One of the reverse genetics tools for analysis
of gene function.
VIRUS INDUCED GENE SILENCING

13.  The first report of VIGS was obtained silencing phytoene desaturase (PDS) gene in Nicotiana
benthamiana.
 Tobacco mosaic virus (TMV) is the first modified virus for application of VIGS methods to plants.
 Tobacco rattle virus (TRV) was also modified to be a tool for gene silencing in plants - N.
benthamiana and tomato.
 Tomato golden mosaic virus (TGMV) - silence a meristematic gene, proliferating cell nuclear antigen
(PCNA) in N. benthamiana
VIGS VECTORS

14. 1. The vector insert
2. VIGS vectors - determined by the plant of interest.
The VIGS vector is a recombinant virus engineered
to be able to carry a piece an endogenous gene
from the host.
3. VIGS vector introduced - Agrobacterium
tumefaciens mediated transient expression or in
vitro transcribed RNA inoculation or direct DNA
inoculation
 In vitro transcription of infectious RNA from a linearized
plasmid DNA template
 Agroinoculation - binary Ti plasmid derived vectors used
for Agrobacterium tumefaciens mediated plant
transformation in which part of a viral genome is inserted
4. Inoculation
5. Assessment of VIGS
MOLECULAR MECHANISM OFVIGS

15. VIGS APPLICATIONS
 Used in post transcriptional gene silencing  Used as a technology for functional genomics

16. Many biochemical and physiological changes were seen due to virus infection and mainly
regulated by virus induced genes.
Nucleic acids and proteins :-
DNA content per cell may increase for some time in a normal expanding leaf.
In TMV-infected leaves, viral RNA may come to represent about 75% of the total nucleic acids
without having any marked effects on the main host RNA fractions.
A reduction in chloroplast ribosomes without a marked effect on cytoplasmic ribosomes is a
fairly common feature for mosaic diseases.
The coat protein of a virus such as TMV can come to represent about half the total protein in
the diseased leaf.
EFFECTS ON PLANT METABOLISM DUE TO VIRUS INDUCED GENES

17. Cont.
A reduction in the amount of the most abundant host protein ribulose bisphosphate
carboxylase oxygenase (rbcs or Rubisco)--is one of the commonest effects of viruses
that cause mosaic and yellowing diseases (e.g. TYMV).
Lipids :- The sites of virus synthesis within the cell almost always contain membrane
structures.
TYMV infection alters the ultrastructure of chloroplast membranes.
Rhabdovirus and Tospovirus particles obtain their outer membrane by budding through
some host-cell membrane.
Carbohydrate :- Virus infection can decrease the rate of accumulation of starch when
leaves are exposed to light.

18. Respiration:- In host-virus combinations where necrotic local lesions develop, there is
an increase in respiration as necrosis develops. This increase is accounted for, at least in
part, by activation of the hexose monophosphate shunt pathway.
Photosynthesis :- Chlorophyll reduction was seen, which affects photosynthesis and
reduction in photosynthesis leads to mosaic symptoms in leaves.
Transpiration :- In chronically virus-infected leaves, transpiration rate and water content
have been found to be generally lower than in corresponding healthy tissues.
Cont.

19. CASE STUDY
The virus infection resulted in significant reductions in plant height, leaf area and number of leaves
produced.
The chlorophyll content of inoculated plants at all stages of growth was lower compared with the healthy
plants.
There were reductions in alkaloids (32.1%), reducing sugars (42.0%), saponins (33.6%), terpenoids
(25.0%) and steroids (15.0%) and increase in glycosides (14.8%) and flavonoids (12.5%).
Significant reductions in lipid (25.0%) and ash (14.6%) and increases in protein (23.4%) and fibre
(10.5%).
 Infection of MWMV also led to significant decreases in the contents of K (48%), Fe (28.6%), Zn (25.0%)
and Mg (22.0%), while Cu recorded 100% increase in inoculated samples.

20. Virus induced genes can leads resistance or susceptible responses.
Susceptible genes are involved in providing proviral conditions and leads to successful
infection of host.
Resistance genes involved in providing antiviral conditions and leads to unsuccessful
infection.
Virus induced genes are also responsible for change in host metabolism and biochemical
and physiological changes in the host.
CONCLUSION

21. REFERENCES :-
 A.A.J. Mofunanya and E.A. Edu, 2015. Physiological and Biochemical Changes in
Cucurbita moschata Duch. Ex. Poir Inoculated with a Nigerian Strain of Moroccan
Watermelon Mosaic Virus (MWMV): Lagenaria breviflora Isolate. International Journal of
Plant Pathology, 6: 36-47.
 B. Singh, S. Kukreja, N. Salaria, K. Thakur, S. Gautam, J. Taunk & U. Goutam. 2019. VIGS:
a flexible tool for the study of functional genomics of plants under abiotic stresses, Journal
of Crop Improvement, 33:5:567-604.
 Garcia-Ruiz, H. 2018. Susceptibility genes to plant viruses. Viruses, 10(9)484.
 Hull R. Plant Virology. 4th ed. Elsevier; New York, NY, USA.