SID-I is implicated in systemic gene silencing in the honey bee

RNA interference (RNAi) has become a powerful functional genomics tool that can be used to effectively silence gene expression. The implications for analysis of loss-of-function phenotypes through systemic or localized silencing are enormously significant in the application of this technology. The Sid-I gene was implicated in the cellular import of RNAi signal that enables passive uptake of dsRNA. Here we demonstrate that RNAi in the honey bee (Apis mellifera) is systemic and our data suggest that honey bee SID-I homologue, a putative transmembrane protein encoded by AmSid-I, is necessary for the uptake of systemically administered dsRNA and subsequent gene silencing. The honey bee SID-I homologue shares strong similarities with human (NP-060169; 44.3%), mouse (NM-198034; 43.9%), and Caenorhabditis elegans (Q9GZC8; 19%). AmSid-I was expressed in the entire set of honey bee tissues examined with the highest abundance in adult head followed by egg tissue. To test the role of AmSid-I in the systemic effect of RNAi, we induced systemic gene silencing of the honey bee Toll-related receptor 18W by a feeding-soaking delivery method of dsRNA and measured expression levels of AmSid-I and Am 18w using real time PCR. A 3.4-fold increase in expression of AmSid-I was observed at 26 h. In contrast, Am 18w gene expression was decreased about 60-fold at 30 h. High mortality and morphological abnormalities were also seen due to gene silencing. The presence of SID-I in honey bees and its function as a transmembrane channel that facilitates uptake of dsRNA are discussed.