Agrobacterium tumefaciens

igocheddarΒιοτεχνολογία

14 Δεκ 2012 (πριν από 4 χρόνια και 8 μήνες)

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Plant Pathogens

Lecture 13

Pathogenic bacteria


Pseudomonas syringae

causes leaf spots


Pseudomonas fluorescens
causes soft rot in
potatoes


Erwinia carotova

causes soft rot


Streptomyces

scabies cases potato scab


Agrobacterium tumefaciens

causes crown gall
disease


Soft Rot


Caused by several different microbes

Stewart's Wilt



Caused by
Pantoea stewartii



Its primary vector is the corn flea beetle


The bacterium lives in the gut of the beetle
during the off season and is spread between
plants when the


beetle feeds on the


seedlings

Crown Gall Disease

ay
reduce
the
value of
a plant
in a
nursery

Crown gall disease does not
usually seriously harm older
plants; however, it may
reduce the value of a plant
in a nursery

The disease causes the
formation of tumor
-
like
swellings called galls that
can generally be found on
the crown of the plant just
above the soil

Crown Gall Disease


Cause by
Agrobacterium tumefaciens



Gram
-
negative, non
-
sporeforming, rod
-
shaped
bacterium


Crown Gall Disease


The disease causes
the formation of
tumor
-
like swellings
called galls that can
generally be found
on the crown of the
plant just above the
soil


Ti plasmid


Most of the disease causing genes are carried on a tumor
inducing (Ti) plasmid


It causes "plant cancer" or what are known as galls. They
are little tumors in which the bacteria can grow and live
in the plant.



The bacterium gets into the plant via some kind of
wound, ie. a scratch.


It injects its plasmid into a plant cell and the plasmid
inserts its DNA into the plant's DNA.


The DNA then directs the plant to make a hollow tumor
where the bacteria can live.

Why do we care about Ti plasmids?


Scientists have taken advantage of the
plasmids ability to insert foreign DNA into a
plant. They take the genes out of the plasmid
that cause galls, and insert genes of interest,


ie. genes for pest resistance and let the plasmid
carry those genes into the plant.



The plant will start making the product you
have engineered it to make.

Green fluorescent protein
-
glowing
Tobacco

How do we control/prevent
bacterial disease in agricultural
products?

Control and Prevention


Biocontrol


Minimize bacterial contamination in
seeds


Sanitize and disinfest seed
-
handling
equipment


Avoid injuring seed and allow cut seed to
heal before planting


Crop rotation will help reduce the
disease


Avoid planting in overly wet or dry soil

Control and Prevention


Avoid over
-
irrigation.


More frequent irrigation for a shorter time
is less favorable for disease.


Do not harvest until plants are fully
mature


Avoid injuries to plant


Provide adequate air flow to promote
drying, particularly when product first
enter storage.


Avoid packing and storing wet product

Biological Control


Agrobacterium tumefaciens
strain K84


Produces
bacteriocins

that inhibit closely
-
related
tumor
-
producing strains.


The bacteriocin, agrosin, is a fraudulent
adenine nucleotide that inhibits DNA
synthesis


It is taken up by strains of A. tumefaciens that
synthesize opines


Virulent bacterial mutant strains that do not
take up the opine are not sensitive to agrosin


Summary


Controlling diseases in crops will be achieved
through


Improved agricultural practices


Genetic engineering of plants to resist pests


New crops will replace conventional crops in
many regions of the world


Biofuels vs. food crops in places like Montana


Global climate change will force changes in
agriculture