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Transgenic plants expressing insect resistance genes

Since first transgenic plant resistant to insects was produced some 20 years ago, a number of novel resistance genes from different origin were discovered and used for plant transformation. First transgenic insect resistant plant contained cry (Bt) gene from bacterium Bacillus thuringiensis. In the middle of 1990's transgenic maize and, some time latter, cotton having cry genes stared to be produced commercially. In the European Union several maize events having cry genes and conferring resistance either to European corn borer (Ostrinia nubilalis Hübner) or western corn rootworm (Diabrotica virgifera virgifera LeConte) have been approved for food and feed, some for cultivation as well. Several other maize events having stacked two or more genes for insect resistance or genes for insect resistance and herbicide tolerance have also been approved. Very effective insecticidal genes named vip, originating also from Bacillus species (B. thuringiensis and B. cereus) are very close to commercial exploitation. Promising results were also obtained when other genes like those for enzyme cholesterol oxidase (microbial origin), avidin (from chicken egg white), chitinase and neuropeptides (insect origin) were used for plant transformation to confer insect resistance. Plants naturally produce different secondary metabolites that, if the expression level of those antimetabolites is high enough, adversely affect insects. A pest insect, in order to be able to feed on some plant species, had to develop resistance to certain antimetabolites that specific plant produces. However, expression of plant resistance genes from other plant species driven by strong promoters enabled development of plants resistant also to pest insects that before easily fed on certain plant species. Genes of three groups of plant protein antimetabolites were used for this purpose: (i) proteinase inhibitors, (ii)  -amylase inhibitors and (iii) lectins. While single proteinase inhibitors have quite narrow spectrum of insecticidal activity, lectins showed insecticidal activity to different orders of insects, even to sap-sucking insects belonging to the order Homoptera. Breeding of new cultivars resistant to insect pests should be continued, and special efforts should be made in production of insect resistant transgenic plants that will hinder the development of insect resistance to the recombinantly- expressed antimetabolites or toxins. Possible way to achieve this is the stacking of two or more insecticidal genes with different mode of action into the same plant. Refuge strategy that diminishes development of insect resistance to Bt toxins also has to be carried out consistently.

transgenic plant; insect resistance; Bt toxin; proteinase inhibitor; avidin

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