Control of a sap-sucking insect pest by plastid-mediated RNA interference

Expression of double-stranded RNAs (dsRNAs) in plastids offers great potential for the efficient control of chewing insects. However, many insect pests do not consume plant tissue, but feed on the host plant by sucking sap from the vascular system. Whether or not plastid-mediated RNA interference (PM-RNAi) can be employed to control sap-sucking insects is unknown. Here we show that five species of sap-sucking hemipteran insects acquire plastid RNA upon feeding on plants. We generated both nuclear transgenic and transplastomic tobacco plants expressing dsRNAs targeted against the MpDhc64C gene, a newly identified efficient target gene of RNAi causing lethality to the green peach aphid, Myzus persicae. In a whole plant bioassay, transplastomic plants exhibited significant resistance to aphids, as evidenced by reduced insect survival, impaired fecundity, and decreased weight of survivors. The protective effect was comparable to that conferred by the best-performing nuclear transgenic plants. We found that the proportion of aphids on mature leaves of transplastomic plants was significantly reduced compared to nuclear transgenic plants. When aphids were allowed to infest only the mature leaves, transplastomic plants grew significantly faster and were overall better protected from the pest compared to nuclear transgenic plants. The insects displayed remarkable alterations in feeding behavior (as monitored by electrical penetration graph analyses and the avoidance response by the aphids), which were different in nuclear transgenic and transplastomic plants, likely reflecting specific avoidance strategies to the toxic RNA molecules. Our data demonstrate that PM-RNAi provides an efficient strategy for controlling at least some sap-sucking insect pests, even though there is most likely no or only very little chloroplast RNA in the sap