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Introduction

Agricultural crops suffer losses due to diseases and pests. Chemical and biological insecticides have been in use for a long time to minimize yield losses due to insect pests. Traditionally, these are externally applied as formulations on crops. The most common biological pesticides used include Cry proteins from Bacillus thuringiensis (Bt), which is a soil bacterium. Bt has a vast collection of cry genes. The encoded proteins vary widely with respect to their insect control efficacy and target insect specificity. It produces crystalline inclusions containing these proteins during sporulation. When ingested by insect larvae, these crystalline inclusions dissociate into monomers in the alkaline insect gut. The monomers further undergo proteolytic cleavage which results in an activated insecticidal protein. This protein binds to the larval gut lining and damages it inducing an antifeeding behavior in the larvae and eventually death. The cry protein binds to the larval gut lining at specific host-encoded receptors. One of the first genes to be commercially exploited for trait development in crops is the Bt cry. This was the advent of plant produced pesticides. A few genes like cry1Ac, cry1F, cry2Ab, have been effectively incorporated into plants for control of insect pests.
   
Rice is the major staple crop for India and many other Asian countries. Yellow stem borer (YSB - Scirpophaga incertulas) is the major lepidopteran pest causing significant yield losses in rice. It is very difficult to control this pest using contact insecticides since it bores into the stem and feeds on tissue affecting the growth and productivity of the tiller. Early infestation results in “dead hearts” while later stage infestation leads to generation of “white heads” or chaffy panicles. Both the symptoms cause yield losses eventually. It is a vital requirement to develop transgenic rice varieties expressing appropriate proteins which could control the pest and prevent yield losses. The added benefit will be the saving in terms of cost and environmental protection due to reduced chemical insecticide sprays.
   
Metahelix has developed rice plants expressing its proprietary, truncated cry1Ac based gene. These plants have been tested under containment conditions for their resistance to YSB. The unique proprietary promoter that has been used to drive the expression of the insecticidal gene facilitates high levels of expression in the culm region, through which the pest larvae bore into the stem. They are due to enter regulatory trials.
 

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