Co-expression of Cocculus hirsutus trypsin inhibitor with Cry1Ab toxin
exhibits insect mortality and reduction in development of resistance in
ChTI (Cocculus hirsutus trypsin inhibitor), a plant serine protease
inhibitor, is a natural plant defense protein effective against
phytophagous insects by inhibiting digestive proteases in guts. We
modified the ChTI gene by codon optimization and expressed it in E.
coli, purified it, and performed insect bioassay, where significant
weight loss with reduced larval growth was observed in both the insect
pests; Helicoverpa armigera and Spodoptera litura. Further, we expressed
the ChTI protein in Arabidopsis thaliana and Solanum lycopersicum,
either individually or pyramided with Bt-Cry1Ab toxin and quantified the
toxicity of the expressed proteins against both insects in the
transgenic plants. We also performed transcriptomic analysis of
transgenic Arabidopsis and tomato plants expressing ChTI protein, where
the enhancement of different pathogenesis-related proteins was observed.
Earlier reports say that insects gradually develop resistance against
toxins, so we developed transgenic plants, co-expressing the two
different toxins from diverse origin, achieving resistance against
insects, and reducing the tendency of insects to develop resistance
against the toxins. Comparative analysis of all the expressed gene
constructs viz. pChTI, pcry1Ab, and pChAb was completed by molecular and
insect biassays. Complete mortality against both insects was observed
without compromising the yield.