Spatio-Temporal and Intra-Plant Expression Variability of Insecticidal Gene&IT (Cry1Ac) &ITin Upland Cotton

Cotton is cultivated on large area of Punjab and Sindh province of Pakistan. The development of transgenic cotton having Bt (Bacillus thuringiensis L.) gene producing delta-endotoxin was a success story to get control of bollworm infestation. Dark side of this story was the progressive development of resistant insects against this toxin. The spatio-temporal expression of the transgene is considered as one of the reasons for resistant pests. Though the transgene is under the control of constitutive promoter, but expression is not consistent and stable throughout the growing season. Therefore, the present study was planned to examine the basis of the variable expression of Bt gene in the genetic background of local cotton accessions. A set of 10 selected Bt genotypes were used to study the season long expression. The plants were sampled for different parts (Leaves and Bolls) at different growth stages (i.e., 30, 60, 90 and 120 days after sowing - DAS). Infra-plant expression variability was also assessed from upper, middle and lower canopy leaves. Enzyme Linked Immuno Sorbent Assay (ELISA) was performed for the quantification of Cry1Ac gene in the sampled tissues at protein level. The results revealed that 30DAS leaves had the highest concentration, while 150 DAS had the least expression. A gradual decrease in the expression was observed throughout the growing season among all the genotypes i.e., with the age of the plant and also with active plant growth. Leaves expressed higher expression as compared to bolls and other reproductive parts. Upper canopy leaves had a considerable higher amount of delta-endotoxin protein followed by middle canopy and lower canopy leaves. The study provided guidelines for the development of better performing Bt cotton genotypes with standard toxin expression. It is concluded that cultivated genotypes don't have stable expression under local climatic conditions. This situation demands, the development of cotton genotypes expressing Cry1Ac transgene at higher level to maximize the benefit of this technology. (C) 2018 Friends Science Publishers