A Combinational Approach of Enhanced Methanol Production and Double Bt Genes for Broad Spectrum Insect Resistance in Transgenic Cotton.

Abstract

The prevalence of insect resistance against Bt toxins has led to the idea of enhancing demethylation from cell wall pectin by pectin methylesterase enzyme for overproduction of methanol which is toxic to insects pests. The AtPME and AnPME fragments ligated into pCAMBIA1301 vector were confirmed through restriction digestion with EcoR1 and BamH1. Excision of 3363bp fragment from 11,850bp vector confirmed the ligation of both fragments into pCAMBIA1301 vector. Transformation of pectin methylesterase-producing genes, i.e., AtPME and AnPME from Arabidopsis thaliana and Aspergillus niger cloned in plant expression vector pCAMBIA1301 under 35S promoter into cotton variety CEMB-33 harboring two Bt genes Cry1Ac and Cry2A, respectively, was done by using shoot apex-cut Agrobacterium-mediated transformation method. The plantlets were screened on MS medium supplemented with hygromycin on initial basis. Amplification of 412 and 543bp, respectively, through gene-specific primer has been obtained which confirmed the successful introduction of pCAMBIA AtPME and AnPME genes into cotton variety CEMB 33. Relative expression of AtPME and AnPME genes through real-time PCR determined the expression level of both gene ranges between 3- and 3.5-fold in different transgenic cotton lines along with quantity of methanol ranging from 0.8 to 0.9% of maximum while 0.5% to 0.6% of minimum but no expression was obtained in negative non-transgenic control cotton plant with least quantity of methanol, i.e., 0.1%. Almost 100% mortality was observed in insect bioassay for Helicoverpa armigera on detached leaves bioassay and 63% for Pink Bollworm (Pectinophora gossypiella) on growing transgenic cotton bolls as compared to positive control transgenic cotton with double Bt genes where mortality was found to be 82% for H. armigera and 50% for P. gossypiella while 0% in negative control non-transgenic plants.