Expression of a Chimeric Gene Encoding Insecticidal Crystal Protein Cry1Aabc of Bacillus thuringiensis in Chickpea (Cicer arietinum L.) Confers Resistance to Gram Pod Borer (Helicoverpa armigera Hubner.)

Abstract

Domain swapping and generation of chimeric insecticidal crystal protein is an emerging area of insect pest management. The lepidopteran insect pest, gram pod borer (<i>Helicoverpa armigera</i> H.) wreaks havoc to chickpea crop affecting production. Lepidopteran insects were reported to be controlled by <i>Bt</i> (<i>cryI</i>) genes. We designed a plant codon optimized chimeric <i>Bt</i> gene (<i>cry1Aabc</i>) using three domains from three different <i>cry1A</i> genes (domains I, II, and III from <i>cry1Aa</i>, <i>cry1Ab</i>, and <i>cry1Ac</i>, respectively) and expressed it under the control of a constitutive promoter in chickpea (<i>cv</i>. DCP92-3) to assess its effect on gram pod borer. A total of six transgenic chickpea shoots were established by grafting into mature fertile plants. The <i>in vitro</i> regenerated (organogenetic) shoots were selected based on antibiotic kanamycin monosulfate (100 mg/L) with transformation efficiency of 0.076%. Three transgenic events were extensively studied based on gene expression pattern and insect mortality across generations. Protein expression in pod walls, immature seeds and leaves (pre- and post-flowering) were estimated and expression in pre-flowering stage was found higher than that of post-flowering. Analysis for the stable integration, expression and insect mortality (detached leaf and whole plant bioassay) led to identification of efficacious transgenic chickpea lines. The chimeric <i>cry1Aabc</i> expressed in chickpea is effective against gram pod borer and generated events can be utilized in transgenic breeding program.