Cry toxin expression in different plant parts of Bt cotton at different phenological stages

Abstract Background Compared to Bollgard-I, the utilization of Cry2Ab protein in Bollgard-II cotton cultivars enhances insect control. Field and laboratory studies demonstrated reduction in the numbers of bollworm-infested terminals, squares, and bolls in Bollgard-II cotton lines when compared to both Bollgard-I and non-Bollgard cotton cultivars. This indicates that the combination of Cry2Ab with Cry1Ac increased the overall expression of proteins. The expression of Cry protein varied across different plant parts, such as leaves, bracts, squares, and bolls. As the season progresses, the expression of Cry protein decreased in these plant parts. Leaves exhibited the highest levels of Cry protein expression, followed by squares, flowers, and bolls. Variation in the expression levels of delta endotoxins in different plant parts was one of the contributing factors to the survival of pest populations on Bt cotton. Results Using a commercially available QL 96 ELISA plate kit, the concentration of delta endotoxin in various plant parts at different phenological stages was determined in twelve BG-II cotton hybrids, namely Ajeet-155, JKCH-2245, RCH-3863, NCS-866, MRC-7373, JKCH-99, MRC-7387, NCEH-21, ANKR-3324, NCSI-1904, and NCHB 9902. Cry1Ac and Cry2Ab protein levels were determined from samples of flowers and fruiting parts (Rind, locule, seed, locule wall and seed) at 40, 75, 100 and 125 days after sowing (DAS) over two consecutive years 2018–2019 and 2019–2020. Cry1Ac protein content and expression was the highest at 100DAS in locule, seed and rind; followed by rind and locule wall and seed in green bolls at 125 DAS; followed by seed, locule, rind and flowers at 75 DAS; followed by flowers at 40 DAS in all the tested twelve Bollgard-II hybrids. Cry2Ab protein content and expression was the highest at 125DAS in locule wall and seed and rind, followed by seed, locule and rind in green bolls at 100 DAS, followed by seed, locule, rind and flowers at 75 DAS, then by flowers at 40 DAS in all the tested twelve Bollgard-II hybrids. Cry1Ac protein expression was less in comparison with Cry2Ab. Conclusions The research findings indicate that the locule of BG-II cotton plants exhibited the highest expression levels of Cry1Ac and Cry2Ab proteins, followed by the seeds, rind, locule wall, and flowers. These results provide valuable insights into the distribution of Cry protein expression in different plant parts, which can contribute to a better understanding of insect control in Bt cotton cultivars.