Insect Resistance Crops

How we can make, some types, ecological factors and d different opinions

By:

- Francisco Muñoz Maestre

Index

1 Introduction

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

9 Conclusion

10 References

Introduction

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 field.

Resistance Genes from Higher Plants

Proteinase inhibitors

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.

Amylase inhibitors

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 expression.

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.

Some Types

Maize

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.

Rice

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%.

Cotton

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.

Ecological Factors

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 reported.

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.

Different Opinions

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).

Conclusion

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 peop le 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 stopp ing the

science develop due to their benefits, they put before the money that people lives, and

this can’t be possible, no nowadays.

References

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