Genetic

Engineering

PLANT DISEASE RESISTANCE

AND GENETIC ENGINEERING

What is a plant disease?

A plant disease is any abnormal condition that alters the abnormal growth or function of a plant. Disease may also reduce yield and quality of harvested product.

Plant diseases are classified in 2 categories:

a) Abiotic

b) Biotic

Abiotic Diseases

Are caused by (non-living) environmental

conditions such as frost, hail, and

chemical burn.

Damage caused by chronic exposure to

air pollutants such as nitrogen dioxide,

sulfur dioxide etc.

Biotic Diseases

Are caused by living organisms such as

fungi, bacteria, viruses, nematodes, etc.

Pathogens may infect all types of plant

tissues to include leaves, shoots, roots,

fruit, seeds etc.

The Disease Triangle

For a biotic disease to occur there must be

a susceptible host plant, the pathogen,

optimum environmental conditions.

The Disease Cycle

The development of visual disease symptoms on a plant requires that the pathogen must

(a) come into contact with a susceptible host

(b) gain entrance or penetrate the host through either a wound, a natural opening or via direct penetration of the host

(c) establish itself within the host

(d) grow and reproduce within or on the host

(e) be able to spread to other susceptible

Biotic Components

Fungi:- They damage plants by killing cells or causing

plant stress. Sources are infected seed, soil, crop debris,

nearby crops and weed, which spread by wind and water splash, and through the movement of contaminated soil etc.

They enter plants through natural openings such as stomata and through wounds caused by pruning, harvesting, hail, insects, other diseases, and mechanical damage.

Common fungal diseases

White blister/White rust

Clubroot

Botrytis rots

Anthracnose

Tuber diseases

Viral Infections

Viruses cause many plant diseases. The spread of most viruses is very difficult to control.

Viruses are often transmitted from plant to plant by insects.

Normally, when a RNA virus attacks a cell, it will produce enormous number of copies of itself. The copies, in turn, produce viral protein, which can help to disable the cells defenses to the virus.

One way of preventing viral infections is by giving a plant a viral gene encoding the virus' 'coat protein'. The plant then produces this viral protein before the virus infects the plant. If the virus arrives, it is not able to reproduce.

This is called co-suppression. When a foreign viral DNA enters the plant cell, viral coat protein is produced, and it eventually shuts down the viral protein's expression. When the virus tries to infect the plant, the production of its essential coat protein is already blocked.

VCPs encapsulate the viral nucleic

acid and are thought to be important in

nearly every stage of viral infection

including replication, movement

throughout an infected plant, and

transport from plant to plant

Alternatively, apical or axillary

meristems are generally free from viral

particles, which has helped the

scientists to produce virus free plants,

by culturing small meristems collected

from virus infected plants.

Gene Transfer in plants

Vector used: Ti plasmid of

Agrobacterium Tumefaciens.

Ti Plasmid- Tumor Inducing Plasmid

with Transfer DNA.

Strategy:

Collect leaf discs

Infect the tissue with Agrobacterium

carrying recombinant Ti plasmid.

The infected tissue is then raised in Shoot regeneration medium for 2-3 days, so that transfer of T-DNA along with gene of interest takes place.

Then the transformed tissues are transferred onto selection cum plant regeneration medium supplemented with usually lethal concentration of an antibiotic.

This medium also contains a bacteriostatic agent, which suppresses the Agrobacterium present with the transformed tissues.

After 3-5 weeks, the regenerated shoots

are transferred to root inducing medium.

After another 3-4 weeks, complete plants

are obtained, which are transferred to soil,

following the hardening of regenerated

plants.

Late Blight in Potato

produce millions of spores from infected

plants under the wet weather conditions

that favor the disease.

Spores produced on infected potatoes can

travel through the air, land on infected

plants, and if the weather is sufficiently

wet, cause new infections.

Late blight is caused by the oomycete

Phytophthora infestans.

Several R genes originating from

introgressions of S. demissum have been

mapped to potato chromosomes using DNA

markers.

the molecular cloning of R1 gene for

resistance to late blight that is located in the

resistance hot spot on potato chromosome V.

R1 among plant resistance genes containing

a conserved nucleotide binding domain

(NBS), a leucine-rich repeat domain (LRR)

and a leucine zipper motif.

300 Restriction fragment length polymorphism(RFLP markers)

Race specific and hyper sensitive to p.infectants

Those groups were R1, R3, R4, R10 and groups with a larger amount of accumulated R alleles and 90 different clones belonging to the species S. demissum, S. tuberosum ssp. andigena, S. phureja, S. bulbocastanum and S. stoloni

Remaining clones in the physical map are

BACs with lengths between 70 and 100

kb.

Grey bars: BACs from the chromosome

carrying r1.

Solid black bars: BACs from the

chromosome carrying R1.

Mapped BAC ends are indicated by the

number of recombinants separating the

BAC end from R1.

References

http://ohioline.osu.edu/hyg-

fact/3000/pdf/PP401_01.pdf

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enes.%20(4).pdf

http://www.gmeducation.org/environment/p

190974-thirsty-plants-rely-on-fungus-for-

help.html