Oral Delivery of Double-Stranded RNAs and siRNAs Induces RNAi Effects in the Potato/Tomato Psyllid, Bactericerca cockerelli

Abstract

The potato/tomato psyllid, Bactericerca cockerelli (B. cockerelli), and the Asian citrus psyllid, Diaphorina citri (D. citri), are very important plant pests, but they are also vectors of phloem-limited bacteria that are associated with two devastating plant diseases. B. cockerelli is the vector of Candidatus Liberibacter psyllaurous (solanacearum), which is associated with zebra chip disease of potatoes, and D. citri is the vector of Ca. Liberibacter asiaticus, which is associated with the Huanglongbing (citrus greening) disease that currently threatens the entire Florida citrus industry. Here we used EST sequence information from D. citri to identify potential targets for RNA interference in B. cockerelli. We targeted ubiquitously expressed and gut-abundant mRNAs via injection and oral acquisition of double-stranded RNAs and siRNAs and were able to induce mortality in recipient psyllids. We also showed knockdown of target mRNAs, and that oral acquisition resulted primarily in mRNA knockdown in the psyllid gut. Concurrent with gene knockdown was the accumulation of target specific ∼ 21 nucleotide siRNAs for an abundant mRNA for BC-Actin. These results showed that RNAi can be a powerful tool for gene function studies in psyllids, and give support for continued efforts for investigating RNAi approaches as possible tools for psyllid and plant disease control.

Emerging strategies for RNA interference (RNAi) applications in insects

“…DsRNAs are the most commonly used RNAi inducers and can be produced in bacteria [38][39][40] or in vitro. [41][42][43][44] Also, siRNAs have been used to induce RNAi effects and down regulate target mRNAs in psyllids (Bactericerca cockerelli) and honeybees (Apis mellifera). 44,45 The siRNAs used in the above examples were produced through the digestion of dsRNAs in vitro by RNase III to generate 18 -25 bp siRNAs.…”

“…[41][42][43][44] Also, siRNAs have been used to induce RNAi effects and down regulate target mRNAs in psyllids (Bactericerca cockerelli) and honeybees (Apis mellifera). 44,45 The siRNAs used in the above examples were produced through the digestion of dsRNAs in vitro by RNase III to generate 18 -25 bp siRNAs. Artificial microRNAs (amiRNAs) can also potentially be used for inducing RNAi effects in insects.…”

“…Recent studies have demonstrated the role of important gene targets such as actin and V-ATPase in mealybugs and psyllids. 44,50,51 Similarly, insect metamorphosis can be influenced by different classes and levels of juvenile hormones (JHs); the levels of JHs in turn can be influenced by JH metabolic enzymes (juvenile hormone esterase, JHE; juvenile hormone epoxide hydrolase, JHEH; juvenile hormone acid methyl transferase, JHAMT). Some of the recent studies in Tribolium showed enhanced RNAi effects when the targets were either juvenile hormone 52,53 or juvenile hormone acid methyl transferase.…”

“…Plutella xylostella larvae, 85 Anopheles gambiae, 86 B. cockerelli 44 and D. citri. 87 Depending on the insect stage, in some cases it was possible to see phenotypic effects on the target insects and in others it was only possible to see target mRNA reductions.…”

“…44 Whiteflies of the genus Bemisia are one of the most important global invasive agricultural insect pests in recent years. 55 The potential of these phloem-feeding hemipterans to develop resistance to chemical insecticides combined with their high reproduction rate has allowed for rapid expansion among many worldwide agricultural areas, 89 and RNAi has brought new hope for potential control strategies.…”