How we can make, some types, ecological
factors andd different opinions
- Francisco Muñoz Maestre
2 Insects Resistance Genes
2.1 Resistance Genes from Microorganisms
2.2 Resistance Genes from Higher Plants
2.3 Resistance Genes from Animals
3 Selectable Marker Genes
4 Promoters and Gene Expression
5 Some Types
6 Ecological Factors
7 Future Technologies
8 Different Opinions
Plants have their own insect resistance mechanism, but sometimes isn’t enough to can
defend against insects. We can improve these mechanisms introducing genes from other
organism which have resistance to target insects.
The first scientific who discovered this was Felix d’Herelle, who use a bacteria to
insects control but the most important appear between 1920 and 1940, Bacillus
thuringiensis (Bt), an aerobic Gram-positive endospore-forming bacterium, isolated the
first time by Shigetane Ishiwata (1901), but Emst Berliner named in 1915 and made
some cultures of this strain.
However, in 1927, Mattes reisolated the strain which were the crystal-forming bacterias
and he discover that this strain killed to flour mouth and rapidly was the heart of the
microbial insect control. In 1987 was the first Insects Resistant crop (I.R.C.), a tobacco
plant in Belgium
Approximately 40 different genes have been introduced into crops and some of them
have been commercialized in several countries. This new technology works as an
additional tool for the control of crop pests and could offer certain advantages over
conventional insecticides, such as more-selective-effective targeting of insects protected
within plants, greater resilience to weather conditions, fast biodegradability, reduced
operator exposure to toxins and financial savings,etc.
Insects Resistance Genes
The insect-resistance genes transferred into plants to date mainly target the insect
digestive system. Most have been derived from a single species of bacterium or from
higher plants, even from animals and other microorganisms. However, the search for
new genes is improve the range of insects affected, to stop the development of
resistance in the target insects by identifying genes with different modes of action and
to improve potency.
Resistance Genes from Microorganisms
Bt is an ubiquitous spore-forming soil bacterium that produces Bt toxins (insecticidal
protein crystals) during the sporulation process and they have been used as microbial
insecticides since the 1950s and, owing to their selectivity, now have an important role
in some integrated pest-management systems. After ingestion by susceptible insects, the
protein is solubilized and activated by proteinases in the insect midgut.
Bt toxins have been transferred and expressed in at least 26 different plant species, but
the level of resistance they confer will, in most cases, depend on whether native-
bacterial or truncated. To date, codon-optimized genes have been transferred into some
crops, like cotton, maize, potato, broccoli, cabbage and alfalfa. Generally, these plants
will express Bt toxins at levels sufficient to kill a high amount of target pests in the
Resistance Genes from Higher Plants
They are Polypeptides, which work naturally in a wide range of plants and are a part of
the plant's natural defence system against herbivory. Proteinases in insects include
serine, cysteine, aspartic and metallo proteinases that catalyse the release of amino acids
and provide the nutrients crucial for normal growth and development.
More than 14 different plant proteinase-inhibitor genes have been introduced into crop
plants but almost effort was concentrated on serine-proteinase inhibitors from the plant
families Fabaceae, Solanaceae and Poaceae, which are targeted mainly against
lepidopteran species but also against some coleopteran and orthopteran pests. The most
active inhibitor identified to date is the cowpea trypsin inhibitor (CpTI), which has been
transferred into at least ten other plant species and affects a wide range of lepidopteran
and coleopteran species; CpTI-transformed tobacco, field-tested in California, caused
significant larval mortality of cotton bollworm (Helicoverpa zea) larvae, but the
protection provided by CpTI was less pronounced and consistent than that of tobacco
containing a truncated Bt-toxin gene.
Genes for three α-amylase inhibitors have been expressed in tobacco, but the main
emphasis to transfer to a plant was the gene for the common-bean (Phaseolus vulgaris)
α-amylase inhibitor (αAI-Pv) to other legumes. αAI-Pv is a thermostable glycoprotein.
αAI-Pv inhibits α-amylase in the midgut of coleopteran stored-product pests of the
genera Callosobruchus and Bruchus and blocks larval development.
Resistance Genes from Animals
Work in this area has, so far, involved primarily serine-proteinase-inhibitor genes from
mammals and the tobacco hornworm (Manduca sexta). Bovine pancreatic trypsin
inhibitor (BPTI), α1-antitrypsin (α1AT) and spleen inhibitor (SI) have been identified
like possible mammals genes which can be introduce into plants to do them resistant to
insects. However, initial results show us that SI or α1AT did not indicate an increased
level of resistance in transgenic potatoes, but M. sexta-derived proteinase inhibitors
expressed in cotton and in tobacco were found to reduce reproduction in B. tabaci
Promoters and Gene Expression
To express transgenes in plant cells, appropriate promoter sequences have to be
introduced into the entire gene to ensure efficient transcription of mRNA. CaMV 35S
(or derivatives of it), has been used in the majority of insect-resistant transgenic plants.
This promoter (from the cauliflower mosaic virus, not completely constitutive) produces
continuous gene expression in most tissues of the plant. However, levels of gene
expression have been reported to vary between different species of plant and different
parts of the plant (transgenic cotton all tissues except mature petals and pollen and
maize in all the plant less pollen or anthers). But the continuous gene expressing give to
the plant resistance in parts where it doesn’t need, so now we are searching promoters
than it expresses in the part which the plant need it
An example is the deployment of a phloem-specific promoter for genes providing
resistance to phloem-sucking insect pests such as aphids.
Introduce native bacterial genes into plant nuclei resulted only in low levels of
expression because native Bt genes are different from that of plant nuclear DNA.
However, Bt toxins are inherently more toxic to insects than the plant-derived gene
products, resulting in a higher level of plant resistance at comparable levels of gene
Gene-expression levels are influenced by a variety of factors, as gene silencing,
variations in expression, environmental conditions, etc.
Selectable Marker Genes
Selectable marker genes are introduced into the insect-resistance gene to can separate
plant cells that have incorporated the new genes from untransformed cells. We use
antibiotic-resistance genes as the selectable marker genes, like bacterial neomycin-
phosphotransferase-ii gene [nptII or APH(3′)II]. A second antibiotic-resistance marker
gene, used for rice and soybean transformation, is the hygromycin-phosphotransferase
gene (hpt, hph or APHIV).
Recent problems with the approval of transgenic maize in the European Community
were based on risks connected with the antibiotic-resistance marker gene, rather than
the insect-resistance gene itself. The current trend is therefore either not to use
antibiotic-resistance marker genes or to deliver the marker gene in a different locus so
that it can later be bred away.
The two/thirds parts of the world hectarage in developing countries are maize crops.
Larvaes from moths can produce yield losses more than 50 % because insecticides can’t
kill eggs into the soil but using I.R.C. more than 40% of the insecticides have been
change to Bt-crops due to the benefits to use it
Millions of hundred of persons have eaten Bt-maize and nobody have found any
problem in the human healthy or in the environment or in other non-target organims.
It is the main food for more than two billion persons, mainly in China, Indonesia and
India, but due to the insecticide use, insects diversity have been reduced drastically and
some companies in China, India are testing Bt-rice, which will decrease the amount of
world insecticide more than 50%.
In developing countries due to insecticide and insect a lot of cotton yields have been
collapsed, but using Bt-cotton some of them solucionated this problem and now there
are more than 33% of Bt-cotton in all the cotton production, in some regions like South
America they produced more than 85% of Bt-cotton.
Cultivars of maize, rice and cotton sown as crops do not have sufficient biological
fitness to survive in natural habitats.
No transgenes have been observed to escape from maize or cotton to a wild relative,
there permanently to initiate a selective advantage.
A large number of studies with Bt-maize, rice and cotton, performed in several
countries, have all shown that the populations of many non-target insects are higher in
fields of Bt-cultivars than in fields of conventional crops regularly receiving
applications of broad-spectrum pesticide.
Bt-proteins are toxic only to selective insect pests but in many cases the cultivation of
Bt-cultivars still requires the application of pesticides, but they don’t need so much
pesticide sprays like with conventional cultivars and spraying chemical pesticides is a
considerable health hazard, especially if hand sprayers are used. These facts provide
overwhelming support for the beneficial effect of Bt-crops cultivation, both for the
environment and for the health of the farm workers and economic aspects.
Although only a few studies have investigated the effects of Cry proteins on earthworms
(L. terrestris, E. fetida, and A. caliginosa), all showed that the Cry1Ab protein had no
significant effects on them.
No toxic effects of Cry proteins on woodlice, collembolans, and mites have been
Few negative effects of Cry proteins from Bt crops on populations of soil nematodes
have been reported
No toxic effects of the Cry proteins on protozoa have been observed.
Fungi appear to be the organisms most affected by Cry proteins in soil.
No significant inhibitory effects of Cry proteins from Bt plants on the activity of some
enzymes have been reported.
Better than insecticides:
The Bt crops doesn’t kill all the insects that contact with them, whereas insecticides do.
"Insecticides generally have a broad spectrum, and they kill a big amount of insects, not
just the pests," said Michelle Marvier of Santa Clara University in California. Bt crops,
Marvier said, are much more specific in their action.
Researchers point out that most studies by industry, which are submitted to government
agencies such as the U.S. Environmental Protection Agency and the U.S. Department of
Agriculture, have been poorly replicated and therefore might have missed important
side effects of the GM crops.
7 Future Technologies
The search for new resistance genes will continue. Examples of recently discovered
toxins include the vegetative insecticidal proteins Vip1, Vip2 and Vip3A, produced by
B. thuringiensis and Bacillus cereus. Different genes will be combined in plants to
increase the range of pests affected and to stop the development of insect resistance to
the gene products. Research is also being directed towards the expression of plant
secondary metabolites, which are usually produced by multigene pathways and may act
on insects by nontoxic modes of action. More-specific promoters, such as inducible
promoters, are needed to replace the CaMV 35S promoter. Efforts are also aimed at
resolving possible environmental factors or endogenous processes influencing the
stability of expression and at overcoming the limitations of conventional marker genes.
An interesting new approach, not yet used with insect-resistance genes, is the new plant
vector system MAT.
Other experiments are searching second and third generation insect-resistant plants
First generation transgenic plants: transgenic plants containing only marker genes,
which are useful in the development of transformation systems.
Second generation transgenic plants: transgenic plants containing, in addition to the
selectable marker, one or two transgenes encoding simple agronomic traits (such as pest
and herbicide resistance).
Third generation transgenic plants: transgenic plants that contain multiple transgenes
targeting multiple pests and diseases, often in a temporal or spatial manner. These might
also express additional value-added or agronomic traits.
Now a days we have a big problem, this technology is almost stopped in the practice
because there are some farmers who want to follow use insecticides, they don’t believe
that changing the plant DNA we can make to this plant resistance to insects, some
others who don’t want that Scientifics change the DNA plant, “we aren’t gods to can
make that, we can make a new specie and destroy the original” and there are other
farmers who only wants use ecological insecticides, like control insects using other
insects or any other organism (biological pest control).
Since 1980s, when appeared the first I.R.C., the technology has improved rapidly, we
can make experiments that people from 1980s couldn’t imagine, but with all this
development, we haven’t get our goal yet, produce all the food that people need, and
still in the 2010s there are people who died because they don’t have anything to bring to
their mouth and this is very sad.
All of us have a role in this, and we can change little by little, if we go in the same
direction, we will get our goal soon, but there are some people who are stopping the
science develop due to their benefits, they put before the money that people lives, and
this can’t be possible, no nowadays.
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