interaction of plants with virus

1. Plant Virus interactions
Class 3

2. Control strategy
• Healthy planting material for vegetatively propagated plants
• Virus free seeds
• Cultural practices that minimize transmission
• Control virus vectors
• Breeding plants for virus resistance

3. Plant Resistance to virus
• Host resistance is the main means of control of plant
virus diseases
• About half of the resistance alleles studied were
dominant, the remainder were either incompletely
dominant or recessive.
• Resistance can operate indirectly, by effects on the
vector, or directly, by preventing virus multiplication
or its deleterious effects within the plant.

4. A number of host factors can affect plant attractiveness to
vectors, and thus the efficiency of virus transmission.
These include physical barriers such as leaf hairs or robust
leaf surfaces, non-preferred foliage colour, secretion of insect
alarm pheromones, and presence in the sap of anti-feedant
chemicals which reduce feeding time and thus time for virus
acquisition and transmission

5. •Passive defenses are due to the failure of the plant to
produce one or more host factors required for virus
reproduction and spread within the host.
• Active defenses include detection and destruction of
the virus-infected cells due to the function of specific
resistance genes in the plant. Normally, resistance genes
are active only against a particular virus
Host response to viral infection

6. Resistance may be separated into three basic types,
operating at three different levels of complexity of the
host population
non-host immunity
An entire species may be resistant to a particular virus with no detectable
symptoms or virus multiplication after attempts at inoculation
Within a species, certain individuals or populations may contain heritable
resistance to a particular virus normally affecting that species: for
cultivated species the resistant population equates to a resistant cultivar
or landrace
Host resistance
Cross protection
plants are deliberately inoculated with a mild strain of an affecting virus to
protect them against subsequent infection by more severe strains

7. Non host immunity /resistance
•Type 1 is the most pre-dominant type of NHR and
presents a basic defense mechanism that prevents
pathogen invasion, e.g., thickening of the cell-wall,
secondary metabolite production, etc. This type of
resistance usually is symptomless
•type 2 NHR is associated with induction of necrosis at
the site of infection, and is induced when pathogens
overcome type 1 resistance. Here, the pathogen is
recognized through specific structures or proteins that
are associated with the pathogen. The recognition of
these structures/proteins, so called microbe associated
molecular patterns (MAMPs) or PAMPS (Pathogen),
takes place by pattern recognition receptors (PRRs) on
plant plasma membranes.

9. Engineered resistance to Plant Virus
1. Plant derived natural R genes ( >200 viral R genes reported)
2. Pathogen derived transgene
3. Non plant and non pathogen derived R gene

10. Engineered Resistance to Plant Viruses
a. Pathogen derived Resistance
Plants are engineered to express viral proteins
transgenically
Papaya ring spot Virus
1990 - $17 million
Rainbow – Kapoho solo
× Sun Up
Sun Up – first genetically
engineered Papaya – CP
of PRSV

13. Naturally occurring R gene

14. First resistance gene against TYLCV, namely Ty-1, which
encodes an RNA-dependent RNA polymerase

15. Recessive resistance
•viruses require host factors (also called susceptibility factors)
to enable an infection
•The inability of interaction between such host factor
and the virus leads to resistance
•The majority of the recessive resistance genes known against
plant viruses have been reported for poty viruses and encode
translation initiation factors of the 4E or 4G family (eIF4E/eIF4G)
•Viruses that encode their own cap-like structure (like potyviruses:
VPg) require interaction with the translation initiation factors
eIF4E/eIF4G for translation

16. Virus induced gene silencing a tool for functional genomics