Oral Delivery Mediated RNA Interference of a Carboxylesterase Gene Results in Reduced Resistance to Organophosphorus Insecticides in the Cotton Aphid, Aphis gossypii Glover

Abstract

BackgroundRNA interference (RNAi) is an effective tool to examine the function of individual genes. Carboxylesterases (CarE, EC 3.1.1.1) are known to play significant roles in the metabolism of xenobiotic compounds in many insect species. Previous studies in our laboratory found that CarE expression was up-regulated in Aphis gossypii (Glover) (Hemiptera: Aphididae) adults of both omethoate and malathion resistant strains, indicating the potential involvement of CarE in organophosphorus (OP) insecticide resistance. Functional analysis (RNAi) is therefore warranted to investigate the role of CarE in A. gossypii to OPs resistance.Result CarE expression in omethoate resistant individuals of Aphis gossypii was dramatically suppressed following ingestion of dsRNA-CarE. The highest knockdown efficiency (33%) was observed at 72 h after feeding when dsRNA-CarE concentration was 100 ng/µL. The CarE activities from the CarE knockdown aphids were consistent with the correspondingly significant reduction in CarE expression. The CarE activity in the individuals of control aphids was concentrated in the range of 650–900 mOD/per/min, while in the individuals of dsRNA-CarE-fed aphids, the CarE activity was concentrated in the range of 500–800 mOD/per/min. In vitro inhibition experiments also demonstrated that total CarE activity in the CarE knockdown aphids decreased significantly as compared to control aphids. Bioassay results of aphids fed dsRNA-CarE indicated that suppression of CarE expression increased susceptibility to omethoate in individuals of the resistant aphid strains.ConclusionThe results of this study not only suggest that ingestion of dsRNA through artificial diet could be exploited for functional genomic studies in cotton aphids, but also indicate that CarE can be considered as a major target of organophosphorus insecticide (OPs) resistance in A. gossypii. Further, our results suggest that the CarE would be a propitious target for OPs resistant aphid control, and insect-resistant transgenic plants may be obtained through plant RNAi-mediated silencing of insect CarE expression.

RNA interference: Applications and advances in insect toxicology and insect pest management

“…Gong et al [49] reported reduced CarE activity associated with increased susceptibility to OPs after oral delivery of a CarE dsRNA to an OP-resistant strain of Aphis gossypii overexpressing CarE. These results demonstrate that the overexpression of CarE plays an important role in OP resistance in this aphid species.…”

“…Furthermore, L. migratoria nymphs injected with CarE9 and CarE25 dsRNAs followed by malathion exposures increased the mortality from 34 to 65% and 54%, respectively [50]. Similarly, in omethoate-resistant A. gossypii, ingestion of dsRNA targeting a CarE led to a 33% reduction of target gene expression, as well as increased susceptibility to omethoate [49]. Moreover, silencing of an aphid CarE (E4) gene with plant-mediated RNAi impaired Sitobion avenae tolerance of phoxim [48].…”

Knockdown of nuclease activity in the gut enhances RNAi efficiency in the Colorado potato beetle, Leptinotarsa decemlineata , but not in the desert locust, Schistocerca gregaria

“…Low sensitivity to RNAi is often observed in dipteran and lepidopteran species, although gene silencing in the latter has been reported in, amongst others, Plutella xylostella, Spodoptera exigua and Manduca sexta (reviewed by Terenius et al, 2011). In contrast, many members of the Hemiptera, Orthoptera and Coleoptera seem to be more responsive, making RNAi more feasible for pest control in these orders (Baum et al, 2007;Gong et al, 2014;Santos et al, 2014). However, there does not appear to be a clear rule to determine the sensitivity of an insect species.…”

Over-expression of CYP6A2 is associated with spirotetramat resistance and cross-resistance in the resistant strain of Aphis gossypii Glover

“…The artificial diet and the rearing method used for this study were according to the methods of Gong et al [31] with some modifications. The diet was prepared in DEPC-treated water to ensure the absence of RNase activity.…”