plant disease resistant and genetic engineering
TRANSCRIPT
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
The%20R1%20gene%20for%20potato%20
resistance%20to%20late%20blight%20(Phy
tophthora%20infestans)%20belongs%20to
%20the%20leucine%20zipper,NBS,LRR%2
0class%20of%20plant%20resistance%20g
enes.%20(4).pdf
http://www.gmeducation.org/environment/p
190974-thirsty-plants-rely-on-fungus-for-
help.html