Designer Plants
Robert Ll. Morris
Robert Ll. Morris
Genetic
engineering has changed commercial plant breeding forever. In years past we
always thought of obtaining new plants by simple breeding and hybridizing. But
to get for instance elms resistant to elm leaf beetle or turfgrass resistant to
Roundup these plants had to be permanently changed in ways that simple breeding
and hybridizing had not been able to accomplish. The major limitation was that
the plants had to be relatively close in their evolutionary history so that a
transfer of new information from one plant to another by traditional breeding
techniques could occur.
engineering has changed commercial plant breeding forever. In years past we
always thought of obtaining new plants by simple breeding and hybridizing. But
to get for instance elms resistant to elm leaf beetle or turfgrass resistant to
Roundup these plants had to be permanently changed in ways that simple breeding
and hybridizing had not been able to accomplish. The major limitation was that
the plants had to be relatively close in their evolutionary history so that a
transfer of new information from one plant to another by traditional breeding
techniques could occur.
All that
has changed with genetic or bioengineering. Over the last twenty years scientists
have discovered that all living organisms have genetic information that is
interchangeable, even between plants and animals. Unlike traditional breeding,
bioengineering has made it possible to select exactly the traits desired from
nearly any living organism and insert them into a plant and create a
genetically modified organism (GMO).
has changed with genetic or bioengineering. Over the last twenty years scientists
have discovered that all living organisms have genetic information that is
interchangeable, even between plants and animals. Unlike traditional breeding,
bioengineering has made it possible to select exactly the traits desired from
nearly any living organism and insert them into a plant and create a
genetically modified organism (GMO).
In Part I
we talked about how the bacterial disease, crown gall, played a role in
bioengineering by providing a biological model for scientists to use to insert
desirable genetic information permanently inside plants. It was known that the
crown gall organism, a bacterium, could infect a plant and insert its own
information causing the plant to do something it normally would not do. In the
undesirable case of the crown gall disease, produce a tumorous swelling of
plant tissue that housed and protected the disease.
More on Crown Gall Disease Organism
we talked about how the bacterial disease, crown gall, played a role in
bioengineering by providing a biological model for scientists to use to insert
desirable genetic information permanently inside plants. It was known that the
crown gall organism, a bacterium, could infect a plant and insert its own
information causing the plant to do something it normally would not do. In the
undesirable case of the crown gall disease, produce a tumorous swelling of
plant tissue that housed and protected the disease.
Scientists
realized that packets of new, desirable genetic information might be inserted
into plants following the same method that crown gall bacterium used. Early in
the development of this technology the crown gall bacterium, modified with
desirable genetic information, was used as the vehicle for transferring genetic
information to plants. The crown gall model of gene insertion eventually led to
the development of new more efficient technologies like “gene guns” which could
“shoot” new information inside of plants.
realized that packets of new, desirable genetic information might be inserted
into plants following the same method that crown gall bacterium used. Early in
the development of this technology the crown gall bacterium, modified with
desirable genetic information, was used as the vehicle for transferring genetic
information to plants. The crown gall model of gene insertion eventually led to
the development of new more efficient technologies like “gene guns” which could
“shoot” new information inside of plants.
Terms like
“gene splicing”, which scientists use to recombine genetic information inside
plants in an attempt to bioengineer a new organism with more desirable traits,
results in “transgenic organisms”. This is a term that can be daunting at first
until it is realized that it just means an organism that was altered or changed
as a result of new genetic information which was purposefully inserted by some
method.
“gene splicing”, which scientists use to recombine genetic information inside
plants in an attempt to bioengineer a new organism with more desirable traits,
results in “transgenic organisms”. This is a term that can be daunting at first
until it is realized that it just means an organism that was altered or changed
as a result of new genetic information which was purposefully inserted by some
method.
Transgenic
organisms usually have some sort of benefit passed on to it from genetic
engineering resulting in an economic benefit to the horticulturist and
ultimately the consumer. These might be new plant traits such as improved
resistance to plant pests like viral yellows or ringspot diseases, acquired
resistance to pesticides such as the Roundup Ready® line of crops,
some dwarfing characteristics in agronomic crops like wheat, the preservation
of food flavors such as in Flavr Savr© tomato lines, and improved resistance to
insect pests by inserting genes from biological organisms that produce toxins
poisonous to insects such as the bacterium Bacillus thuriengensis (Bt).
organisms usually have some sort of benefit passed on to it from genetic
engineering resulting in an economic benefit to the horticulturist and
ultimately the consumer. These might be new plant traits such as improved
resistance to plant pests like viral yellows or ringspot diseases, acquired
resistance to pesticides such as the Roundup Ready® line of crops,
some dwarfing characteristics in agronomic crops like wheat, the preservation
of food flavors such as in Flavr Savr© tomato lines, and improved resistance to
insect pests by inserting genes from biological organisms that produce toxins
poisonous to insects such as the bacterium Bacillus thuriengensis (Bt).
Bt pesticide sprays for controlling
insects have been available to commercial applicators and homeowners as a form
of “natural” or “biological” pest control since the early 1960’s under a
variety of different names. The first release of a Bt spray had a very narrow
range of insects that it would control. Larvae of moths and butterflies with an
alkaline gut pH and that fed largely on leaf surfaces were the only targets.
This narrow range in pests that it controlled was both good and bad. It was
good since it was very safe for humans and other animals that weren’t larvae of
moths and butterflies such as beneficial insects. It was bad since it
controlled such a narrow range of insects and these only in their larval stages.
insects have been available to commercial applicators and homeowners as a form
of “natural” or “biological” pest control since the early 1960’s under a
variety of different names. The first release of a Bt spray had a very narrow
range of insects that it would control. Larvae of moths and butterflies with an
alkaline gut pH and that fed largely on leaf surfaces were the only targets.
This narrow range in pests that it controlled was both good and bad. It was
good since it was very safe for humans and other animals that weren’t larvae of
moths and butterflies such as beneficial insects. It was bad since it
controlled such a narrow range of insects and these only in their larval stages.
We now recognize this particular
strain of Bt as the variety kurstaki.
Since the 1980’s there have been 50 strains of Bt developed that are specific
to not only moth and butterfly larvae but larvae of other insects such as the
elm leaf beetle (Bt var. tenebrionus),
fungus gnats (Bt var. israelensis),
and a wide range of agricultural pests including beetles. All the different
Bt’s had the same basic scenario however; the susceptible juvenile insect eats
plant foliage that has the bacterium on its surface, Bt spores are ingested by
larvae, the spores grow and reproduce inside the insect producing toxins, toxins
paralyse the digestive tract of the larvae causing it to cease eating, insect
death. Death can range anywhere from a few hours to 5 days after ingestion.
This depends on the amount of Bt ingested, the size and variety of the larvae
and variety of Bt used for control.
strain of Bt as the variety kurstaki.
Since the 1980’s there have been 50 strains of Bt developed that are specific
to not only moth and butterfly larvae but larvae of other insects such as the
elm leaf beetle (Bt var. tenebrionus),
fungus gnats (Bt var. israelensis),
and a wide range of agricultural pests including beetles. All the different
Bt’s had the same basic scenario however; the susceptible juvenile insect eats
plant foliage that has the bacterium on its surface, Bt spores are ingested by
larvae, the spores grow and reproduce inside the insect producing toxins, toxins
paralyse the digestive tract of the larvae causing it to cease eating, insect
death. Death can range anywhere from a few hours to 5 days after ingestion.
This depends on the amount of Bt ingested, the size and variety of the larvae
and variety of Bt used for control.
Bt became popular in the past
because it had some distinct advantages over other pesticides: it had a low
hazard to humans; there was no waiting period from time of application before
re-entering the field; different strains of Bt didn’t harm beneficial or non-target
insects; insects that died from Bt were not dangerous to predators; Bt was not
known to cause injury to plants on which it had been applied and was not
considered harmful to the environment; and, little or no insect resistance had
been reported.
because it had some distinct advantages over other pesticides: it had a low
hazard to humans; there was no waiting period from time of application before
re-entering the field; different strains of Bt didn’t harm beneficial or non-target
insects; insects that died from Bt were not dangerous to predators; Bt was not
known to cause injury to plants on which it had been applied and was not
considered harmful to the environment; and, little or no insect resistance had
been reported.
More on Bacillus thuringiensis or Bt
The major problem with Bt applied
as a pesticide was its lack of persistence in the environment (sunlight and
rain shortened its life) and it had to be eaten by the insects to work and only
the larval stages of the insect were susceptible. Multiple applications needed
to be applied with just the right timing or its chances of success were
limited.
as a pesticide was its lack of persistence in the environment (sunlight and
rain shortened its life) and it had to be eaten by the insects to work and only
the larval stages of the insect were susceptible. Multiple applications needed
to be applied with just the right timing or its chances of success were
limited.
But what if
the Bt toxin could be inserted into the plant? The toxin would always be
present so timing was not a problem. Persistence was not a problem since the
plant protected and even produced the toxin. To insert the Bt toxin gene (lets
call it X gene) the scientists first identify the right Bt. Next they isolate
the X gene and remove it from the Bt bacterium. They then attach a second gene,
a gene that provides resistance to a toxic chemical such as an antibiotic or
herbicide, to the Bt gene. Lets call the second gene the Y gene. The X gene,
with the attached Y gene, is inserted into plant cells. Any plant cell that has
the toxic X gene now is given resistance to an applied toxic chemical due to
the presence of the Y gene.
the Bt toxin could be inserted into the plant? The toxin would always be
present so timing was not a problem. Persistence was not a problem since the
plant protected and even produced the toxin. To insert the Bt toxin gene (lets
call it X gene) the scientists first identify the right Bt. Next they isolate
the X gene and remove it from the Bt bacterium. They then attach a second gene,
a gene that provides resistance to a toxic chemical such as an antibiotic or
herbicide, to the Bt gene. Lets call the second gene the Y gene. The X gene,
with the attached Y gene, is inserted into plant cells. Any plant cell that has
the toxic X gene now is given resistance to an applied toxic chemical due to
the presence of the Y gene.
Researchers then multiply the plant
cells in the presence of the antibiotic or herbicide and kill all cells that do
not have the Y gene. Because the X and Y genes are attached, the resulting
cells will contain the Bt toxin. These genetically transformed plant cells are
then grown into whole plants by a process called tissue culture. The modified
plants produce the same lethal Bt protein produced by Bt bacteria because the
plants now have the same gene.
cells in the presence of the antibiotic or herbicide and kill all cells that do
not have the Y gene. Because the X and Y genes are attached, the resulting
cells will contain the Bt toxin. These genetically transformed plant cells are
then grown into whole plants by a process called tissue culture. The modified
plants produce the same lethal Bt protein produced by Bt bacteria because the
plants now have the same gene.
The insertion of the toxic genes
from Bt into plant lines so that plant itself becomes toxic is under quite a
bit of controversy. First and foremost is that growing plants that continually
have the Bt toxin present increases the chance that insects feeding on these
plants may become resistant to the Bt gene.
from Bt into plant lines so that plant itself becomes toxic is under quite a
bit of controversy. First and foremost is that growing plants that continually
have the Bt toxin present increases the chance that insects feeding on these
plants may become resistant to the Bt gene.
There is some recent research that
has demonstrated that this has already happened. Problems arise primarily
because the Bt toxin is always present through the plants life cycle and that
it is in all plant parts. Because susceptible insects must ingest the Bt toxin
to be poisoned, genetically engineered cells could be directed to plant parts
that only the target pest will eat or at certain times of the year. Scientists
have been working on a Bt gene that will “switch on” in plant parts that are
green (leaf tissue) or “switch off” in other plant parts that are not green
(flowers, pollen and seed). Plants receive genes with a genetic “promoter
switch” that results in production of the Bt toxin only in certain plant parts.
has demonstrated that this has already happened. Problems arise primarily
because the Bt toxin is always present through the plants life cycle and that
it is in all plant parts. Because susceptible insects must ingest the Bt toxin
to be poisoned, genetically engineered cells could be directed to plant parts
that only the target pest will eat or at certain times of the year. Scientists
have been working on a Bt gene that will “switch on” in plant parts that are
green (leaf tissue) or “switch off” in other plant parts that are not green
(flowers, pollen and seed). Plants receive genes with a genetic “promoter
switch” that results in production of the Bt toxin only in certain plant parts.