Cloning and Functional Characterization of a Double-Stranded RNA-Degrading Nuclease in the Tawny Crazy Ant ().

RNA interference is a powerful tool that post-transcriptionally silences target genes. However, silencing efficacy varies greatly among different insect species. Recently, we attempted to knock down some housekeeping genes in the tawny crazy ant (), a relatively new invasive species in the southern United States, but only achieved relatively low silencing efficiency when dsRNA was orally administered. Here, we detected divalent cation-dependent, dsRNA-degrading activity in the midgut fluid of worker ants in assays. To determine whether dsRNA degradation could contribute to low effectiveness of oral RNAi in , we cloned its sole gene (). The deduced amino acid sequence contained a signal peptide and an endonuclease domain. Sequence alignment indicated a high degree of similarity with well-characterized dsRNases, particularly the six key residues at active sites. We also identified dsRNase homologs from five other ant species and found a tight phylogenetic relationship among ant dsRNases. is expressed predominantly in the abdomen of worker ants. Oral delivery of dsRNA of significantly reduced the expression of transcripts, and substantially suppressed dsRNA-degrading activity of worker ants' midgut fluids as well. Our data suggest that dsRNA stability in the alimentary tract is an important factor for gene silencing efficiency in , and that blocking NfdsRNase in gut lumen could potentially improve RNAi, a novel pest management tactic in control of and other ant species.