Abstract
Myzus persicae is a major pest of many crops including canola and Brassica vegetables, partly because it vectors plant viruses. Previously it has been reported that double-stranded RNA delivered to aphids by injection, artificial diet or transgenic plants has knocked down target genes and caused phenotypic effects. While these studies suggest that RNA interference (RNAi) might be used to suppress aphid populations, none have shown effects sufficient for field control. The current study analyses the efficacy of dsRNA directed against previously reported gene-targets on Green peach aphid (Myzus persicae) strains. No silencing effect was observed when dsRNA was delivered in artificial diet with or without transfection reagents. dsRNA produced in planta also failed to induce significant RNAi in M. persicae. Transcriptome analyses of the midgut suggested other potential targets including the Ferritin heavy chain transcripts, but they also could not be knocked down with dsRNA. Here we show that dsRNA is rapidly degraded by midgut secretions of Myzus persicae. Analysis of the transcriptome of the M. persicae midgut revealed that an ortholog of RNases from other insects was abundant.
Highlights
The first publication of successful RNA interference (RNAi) in aphids reported that microinjecting short interfering RNA’s into adult pea aphids (Acyrthrosiphon pisum), knocked down the transcripts of C002, a gene that is usually highly expressed in the salivary glands[13]
Transcript levels of C002 were significantly reduced by three days post-injection, and led to insect death by eight days, compared to 16 days for aphids injected with a control short interfering RNA (siRNAs) sequence
In contrast to a previous study on pea aphids (Acyrthrosiphon pisum) we were unable to elicit gene knockdown by feeding aphids vATPase-like dsRNA in an artificial diet, even though we were using higher concentrations of dsRNA (20 ng/μl in the grain aphid[39] versus 37.5 ng/μl in the present study)
Summary
The first publication of successful RNAi in aphids reported that microinjecting short interfering RNA’s (siRNAs) into adult pea aphids (Acyrthrosiphon pisum), knocked down the transcripts of C002, a gene that is usually highly expressed in the salivary glands[13]. Dietary dsRNA has been delivered to aphids via artificial diet droplets placed between two sheets of parafilm[5,16] Using this approach, pea aphids fed dsRNA homologous to vATPase (a gene successfully targetted in the initial beetle study1) exhibited ~32% reduction in transcript abundance after three days and, remarkably, achieved www.nature.com/scientificreports/. Another study reported that dsRNA directed to aquaporin via artificial diet sachets, reduced transcripts of this gene by more than 50%17 This treatment did not affect aphid weight, a reduction in the osmotic pressure of the hemolymph was observed - as expected from the knockdown of this gene. Another study used transient transfection of N. benthamiana leaf discs to express dsRNA targeting three aphid genes (aquaporin, sucrase and a sugar transporter) individually and in combination and found that the combined treatment yielded a greater effect on the hemolymph osmotic pressure and body weight than the individual dsRNA treatments[19]. This fecundity effect elicited by C002 dsRNA has been reported in a second study by the same research group but was only detected when the aphids were exposed to transformed plants over several generations[17]
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