inositol hexaphosphate pathways couple to RNA interference and pathogen defense.

RNA interference (RNAi) is an evolutionarily conserved pathway that defends against viral infections in diverse organisms. mutations that enhance RNAi have revealed pathways that may regulate antiviral defense. A genetic screen for mutations that fail to up-regulate a defense response reporter transgene detected mutations that enhance RNAi to silence this reporter gene in the inositol polyphosphate multikinase , the synMuv B gene and the pathogen defense response gene . Using other assays for enhanced RNAi, we found that the alleles and an gene inactivation of a later step in inositol hexaphosphate (IP) synthesis, and the and alleles enhance RNAi. IP has been known for decades to bind and stabilize human adenosine deaminase that acts on RNA (ADAR) as well as the paralog tRNA editing ADAT. We show that the IP pathway is also required for mRNA and tRNA editing. Thus, a deficiency in two axes of RNA editing enhances the already potent RNAi antiviral defense, suggesting adenosine to inosine RNA editing may normally moderate this siRNA antiviral defense pathway. The IP-deficient mutants are synthetic lethal with a set of enhanced RNAi mutants that act in the polyploid hypodermis to regulate collagen secretion and signaling from that tissue, implicating IP signaling especially in this tissue. This enhanced antiviral RNAi response uses the RIG-I-like receptor DRH-1 to activate the unfolded protein response (UPR). The production of primary siRNAs, rather than secondary siRNAs, contributes to this activation of the UPR through XBP-1 signaling. The and mutants that also emerged from this screen act in the mitochondrial defense pathway rather than by enhancing RNAi.