Plant Biotechnology

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Oct 22, 2013 (3 years and 7 months ago)

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Plant Biotechnology

Chapter 6

Motivation for genetically
engineered crops


Agriculture is the biggest industrial sector
in the world


$1.3 trillion of products/year


Over past 40 years, world population has
doubled while agricultural land area has
increased by only 10%

Plant transgenics


Transfer of genes to plants directly
accelerates selective breeding practices
used in the past.


Cotton fiber strength


increased 1.5% per year through conventional
breeding


Increased 60% by inserting a single gene into the
plant


Corn and soybean have been targets of much
genetic engineering


Cloning


Many types of plants can regenerate from a
single cell, similar to a bacterium.


The resulting plant is a clone or replica of
plant from which original cell was taken.


Protoplast fusion


Introducing a gene into a “denuded” plant cell
and generating a new plant

Genetic engineering techniques
applied to plants

Protoplast fusion

Callus cells

Plant A

Plant B

Hybrid plant

Leaf fragment technique

Agrobacterium tumefaciens
as a vector for
transferring foreign genes into plant
chromosome


This bacterium naturally infects plant cells
causing cancerous growths
-

crown gall
disease


Infection (
vir
) genes carried on Ti plasmid

Infection Process


Vir genes copy T
-
DNA


Open channel in bacterial
cell membrane for T
-
DNA
to pass through


T
-
DNA enters plant through
wound, integrates itself into
plant chromosome

http://www.bio.davidson.edu/people/kabernd/seminar/2002/method/dsmeth/ds.htm

Leaf fragment technique used to
introduce foreign genes into plant


Small discs are cut from plant leaf


Discs are cultured to start a new plant


Early in the regeneration process, the bacterium
Agrobacterium tumefaciens

carrying a Ti
plasmid is introduced into the culture


The plasmid DNA combines with the plant
chromosome


Discs are treated with hormones to encourage
shoot and root development and then the new
plant is planted in the soil


Make leaf discs

Briefly culture

discs with

genetically

modified

Agrobacterium

Transfer to filter

paper over nurse

cells


Culture 2
-
3 days

Transfer to shoot stimulating medium

Leaf fragment technique

Agrobacterium

with Ti plasmid

with foreign gene

Gene guns

Gene

gun

stopped

Antisense technology


Used to produce the Flavr
-
Savr tomato in
1994.


Enzyme polygalacturonase breaks down
structural polysaccharide pectin in wall of a
plant.


This is part of the natural decay process in a
plant


Monsanto identified the gene than encodes
the enzyme and made another gene that
blocked the production of the enzyme.

Antisense molecules

Natural insecticide produced by soil
bacterium


The bacterium
Bacillus
thuringiensis
produces
a crystalline protein
that if ingested by
insects acts as a toxin
and kills the insect


Farmers used to spray
their fields with spores
of the bacteria to
inoculate the plant leaf
surface before it is
attacked by the insect


Insecticide biotechnology


The gene coding for the
crystalline protein (Cry) was
transferred from the bacterium
to the plant.


How can they do this?


Now the plant produces the
toxin protein, so don’t need to
inoculate with bacterium


This strategy kills the pest before
it kills the plant

Plant vaccines


Plants are susceptible to diseases caused by
viruses (tobacco mosaic virus)


Virus surface protein induces an immune
response in the plant against the virus
protein


Researchers inserted the virus protein into
the plant genome using the Ti plasmid/
Agrobacter

vector


Now the plant produces a small quantity of
the protein which elicits an immune response
by the plant the way a vaccine does

Concerns about genetically
modified foods


Human health


Unsuspected allergens


What other issues are there?


Environment


Messing up the gene pool of non
-
target
species in the environment


Lateral gene transfer in nature


Still poorly understood in nature

National biofuels initiative


In 2007, the federal government increased
funding for research in biofuels (ethanol and
biodiesel)


Idea was to


produce ethanol from corn


convert agricultural waste products
(lignocellulose) to ethanol


This requires re
-
engineering natural
biochemical pathways in plants or microbes
to produce more fuel as an end
-
product

How is ethanol produced?


Most ethanol is produced using a four
-
step
process:


The ethanol feedstock (crops or plants) are
ground up for easier processing


Sugar is dissolved from the ground material,
or the starch or cellulose is converted into
sugar


Microbes feed on the sugar, producing
ethanol and carbon dioxide as byproducts


The ethanol is purified to achieve the correct
concentration.


Metabolic engineering to improve efficiency
of biological production of biofuels

Natural metabolic pathway

1 ton of Feedstock X product A product
D

product
E

150 gal
Ethanol

Genetically engineered metabolic pathway

1 ton of Feedstock X product A product
B

product
C

50 gal

Ethanol

product
G

50 gal
Butanol


New enzyme

Benefits of ethanol


Overall, ethanol is considered to be better
for the environment than gasoline.


Ethanol
-
fueled vehicles produce lower carbon
monoxide and carbon dioxide emissions, and
the same or lower levels of hydrocarbon and
oxides of nitrogen emissions.


Ethanol is widely available and easy to use


Ethanol is good for the economy

Drawbacks of ethanol as a biofuel


Creating plant
-
based biofuels requires too
much farmland to be practical or
sustainable

land that would be better
used to grow food.



Producing ethanol and other biofuels takes
more energy than the fuel can generate.

Summary


Variety of techniques are available to
introduce genes into plants and have the
plants express the gene


Such genetic engineering is used to


Improve disease resistance


Flavor of product


Nutrition of product


Shelf life of product


Any other property of plant that improves its
value


Advances in biotechnology of biofuel
production will be the next greatest
application of our knowledge of biology to
address challenges to our society and
high
-
maintenance lifestyles.