A nuclease specific to lepidopteran insects suppresses RNAi.

Guan RB , Li HC , Fan YJ , Hu SR , Christiaens O , Smagghe G , Miao XX
The Journal of biological chemistry
More than 70% of all agricultural pests are insects in the order Lepidoptera, which, unlike other related insect orders, are not very sensitive to RNAi, limiting genetic studies of this insect group. However, the reason for this distinct lepidopteran characteristic is unknown. Previously, using transcriptome analysis of the Asian corn borer, we identified a gene, termed, that is up-regulated in response to dsRNA. Here, we report that this Lepidoptera-specific gene encodes a nuclease that contributes to the RNAi insensitivity in this insect order. Its identity was experimentally validated, and sequence analysis indicated thatencodes a previously uncharacterized protein with homologous sequences in seven other lepidopteran species. Its computationally predicted three-dimensional structure revealed a high structural similarity to human exonuclease I. Exposure to dsRNA instrongly up-regulated this gene's expression, and the protein could digest ss and ds RNA and DNA both in vitro and in vivo. Of note, we found that this up-regulation ofexpression is faster than that of the gene encoding the key RNAi-associated nucleaseknockdown insignificantly enhanced RNAi efficiency. Moreover,overexpression insuppressed RNAi efficiency. Finally,knockdown significantly increased the amount and diversity of small RNAs. Therefore, we renamed this protein RNAi efficiency-related nuclease (). In conclusion, we propose thatmay explain why lepidopterans are refractory to RNAi and represents a target for further research on RNAi efficiency in this insect order.

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