Heterologous expression of cry3Bb1 and cry3 genes for enhanced resistance against insect pests in cotton

Transgenic technology played a crucial role in developing insect-resistant plants resulting in the reduced application of pesticides. This article reports the expression of two cry proteins (Cry3Bb1 and Cry3) in cotton for enhanced resistance against chewing insect pests. The aforementioned genes were synthetically developed and were cloned under appropriate regulatory sequences followed by transformation into Eagle-2 genotype (Gossypium hirsutum) of cotton through shoot apex-cut Agro-infiltration. The transgene integration was validated by polymerase chain reaction using primers flanking the aforementioned cry genes. Transgene expression was assessed by qRT-PCR using GADPH as a reference gene. The relative fold expression analyses revealed the highest expression of the transgene(s) in M1 plants, which is a 4.5-fold expression (Cry3 + Cry3Bb1) followed by M3 (fold expression, 3.0) (Cry3Bb1) and M2 (fold expression, 2.5) (Cry3) transformants of cotton. The confirmed transgenic plants were exposed to insect pests, pink bollworm (Pectinophora gossypiella), and army bollworm (Helicoverpa armigera). Bioassay results revealed that 60% mortality was observed against pink bollworm, and 75% mortality was observed against army bollworm in transgenic plants containing both Cry3Bb1 and Cry3 genes (M1 transgenic plants). In M2 transgenic plants containing only the Cry3Bb1 gene, the mortality was observed to be 40% in the pink bollworm population, whereas 45% mortality was observed in the army bollworm population. In the case of M3 transgenic plants containing single gene-Cry3, the mortality was 20% in the pink bollworm population, whereas 30% mortality was observed in the army bollworm population. Almost no mortality was observed in non-transgenic Eagle-2 control plants. Hence, the developed cotton transformants have improved resistance against chewing insect pests.