Effect of Drought and Salinity Stress on the Expression Level of Cry1Ac Endotoxins in Transgenic Bt Cotton

Abstract

Cotton is a vital fiber crop and major agricultural product worldwide. It was genetically engineered with Cry genes from Bacillus thuringiensis (Bt), producing insecticidal proteins called Cry (Bt) toxins. Bt cotton efficacy depends on the expression level of these toxins, which abiotic stress negatively affects. This study examined how salinity and drought stress influence Cry1Ac endotoxin levels in transgenic Bt cotton. Initially, Cry1Ac transgene presence was confirmed using polymerase chain reaction (PCR) and immunostrip assays. Genotypes were then subjected to varying levels of salinity and drought stress under controlled conditions. Bt toxin levels were quantified using a commercial ELISA kit. Results showed that increasing drought and salt stress led to a decline in Bt protein expression. Toxin concentrations in genotypes MNH-886 and Bt-121 varied across different exposure durations (days three and six) during salinity treatment. FH-113 and 3701 genotypes exhibited variable Bt protein expression in response to drought. Specifically, genotype FH-113 exhibited higher toxin levels under drought conditions (20% PEG) compared to genotype 3701. These findings indicate that genetic background influenced Bt toxin expression under drought stress. In conclusion, increasing salinity and drought result in decreasing Cry1Ac toxin levels, which may negatively impact insect resistance efficacy of Bt cotton.