Expression and function of a hybrid Bt toxin gene in the transgenic rice conferring resistance to insect pests

Abstract

A hybrid Bt toxin gene was made from cryIA(b) and cryIA(c) after optimization of their codon usage to meet high G+C content in rice and placed under control of the rice Actin I promoter along with its first intron. This hybrid Bt toxin gene was introduced into the genome of an elite indica rice cultivar IR72 through biolistic method. Five independent transformants were identified out of 27 transgenic plants obtained. The level of the hybrid Bt toxin was estimated to be 0.01%-0.20% of the total soluble protein in leaf or stem tissue of the transgenic plants. This considerable range of expression levels was studied for a strong insecticidal effect. As demonstrated by insect bioassay, neonate larva mortality rates of yellow stem borer (Scirpophaga incertulas) (YSB) for selected T₀ transgenic rice plants as well as T₂ homozygous lines were 100%. This is the first report of a hybrid Bt toxin gene [cryIA (b) and cryIA(c)] driven by rice Actin I promoter in any cereal crop including rice conferring resistance to insect pest. The present hybrid Bt toxin gene deployment strategy will provide sustainable insect pest resistance in rice.