Insect Control by the Expression of Long Double-Stranded RNA in Plastids

Double-stranded RNAs (dsRNAs) targeted against essential genes can trigger a lethal RNAi response in insect pests. However, although expression of dsRNAs targeted against insect genes in transgenic plants has impaired growth and development, complete protection of the plants and efficient killing of the insects were not achieved due to the presence of an endogenous RNAi pathway in plants that processes dsRNAs into short interfering RNAs (siRNAs). We found that long dsRNAs can be stably produced in plastids, a cellular compartment that appears to lack an RNAi machinery. When expressed from the chloroplast genome, dsRNAs accumulated to as much as 0.4% of the total cellular RNA. Transplastomic potato plants producing dsRNAs targeted against the β-actin gene of the Colorado potato beetle, a notorious agricultural pest, were efficiently protected from herbivory and were lethal to its larvae. Thus, plastid-expressed long dsRNAs can provide full crop protection without chemical pesticides and without synthesis of foreign proteins in the plant. Shifting the target of transgesis from the nucleus to the plastid removes the major hurdle on the way to exploiting transgenically delivered RNAi for efficient crop protection in the field.