Transformation of the nuclear genome of plants with genes (e.g. Bt genes) to confer insect resistance gives very low levels of expression unless extensive modifications are carried. Whereas, introduction of the same genes into the plastid genome results in high levels of toxin accumulation as the plastid genome is bacterial in origin [81] . Therefore, the insect resistance genes were investigated for high-level expression from the plastid genome [3] . Hence, when insect resistance genes are expressed into the plastid genome, leaves of these transplastomic plants proved highly toxic to herbivorous insect larvae.