The SID-1 double-stranded RNA transporter is not required for systemic RNAi in the migratory locust

Systemic RNAi, the spreading of RNAi effects to cells and tissues that have not initially encountered a dsRNA trigger, is a common phenomenon in many organisms. However, the underlying mechanisms of systemic RNAi remain largely unknown. Here, we studied the characteristics and possible mechanisms of systemic RNAi in Locusta migratoria. We observed that the locust has pronounced sensitive systemic RNAi in response to dsRNA injection for both broadly-expressed as well as tissue-specific genes. Only a 30 pg (dsRNA/mg tissues) dose could induce significant systemic RNAi effects. Only one SID-1 ortholog (LmSID-1) was identified in the locust genome, which exhibited a progressively increasing expression pattern with development and its expression was enriched in the gonad. To test the role of LmSID-1 in systemic RNAi, we performed in vitro and in vivo experiments. The results from in vivo experiments showed that silencing of LmSID-1 gene dose not influence RNAi effects of other genes. The results from in vitro experiments confirmed that the expression of the LmSID-1 protein in Drosophila S2 cells could not enhance dsRNA uptake. Thus, these findings imply the existence of alternative mechanisms underlying insect systemic RNAi, which may be different from Caenorhabditis elegans or mammals.