GENOTYPE-DEPENDENT REGULATION OF δ-ENDOTOXIN REVEALS THAT INSECT-RESISTANT COTTON CONTAINS TOXIN PREDOMINANTLY IN SEEDS

Engineered insecticidal delta-toxins protect cotton genotypes against devastating insects but the accumulated amount of toxin varies during the growth period, generating conflicting results. Here we report varied effects of cry1Ac gene, driven by CaMV 35S promoter, in aerial parts of cotton plant including seed under different growth and environmental regimes. Data is recorded after every 20 days, starting from 60 to 120 DAS at temperatures 25 degrees C, 35 degrees C, 40 degrees C and 50 degrees C. An increasing trend in the concentration of delta-toxin in leaves is observed from 60 to 100 DAS and at temperature from 25 degrees C to 40 degrees C, and is decreased at 120 DAS and 50 degrees C. The levels of accumulated toxin are significantly higher in MNH-886 compared to FH-142, irrespective to temperature and age of the plants, demonstrating that MNH-886 is more stable genotype for transgene expression and for effective insect control. Interestingly, transprotein is accumulated 28% and 130% higher in seeds (3.6 mu g g(-1)) than in the leaves (2.8 mu g g(-1)) and 15 DAP locules (1.59 mu g g(-1)); respectively, suggesting that varied expression is due to interaction of 35S promoter with environmental factors, plant growth and development. Insects Pectinophora gossypiella, Helicoverpa armigera and Spodoptera litura are serious threats to cotton crop. First two damage bolls whereas later attacks on leaves thereby results in loss of photosynthetic area on leaves consequently lower the yield. This calls for tissue-specific or inducible engineering of toxins in cotton for effective control of insects and biosafety of non-target animals and human being since they feed on seedcake and cotton seed oil respectively.