Foliar-applied double-stranded RNA is mobile, transfers to plant pathogens, and triggers RNAi.

Foliar application of double-stranded RNA (dsRNA) as RNA interference (RNAi)-based biopesticides represents a sustainable alternative to chemical-based crop protection strategies. A key feature of RNAi in plants is its ability to act non-cell autonomously, a process that plays a critical role in plant development and protection against pathogens. Whether RNAi induced by foliar dsRNA application acts non-cell autonomously remains debated, with the mechanisms and implications of this movement largely unexplored. We show that upon foliar application, dsRNA enters the leaf vasculature and moves to vegetative, reproductive, and belowground tissues in multiple plant species. Unprocessed mobile dsRNA was detected in the apoplast, being maintained in new growth, indicating apoplastic rather than symplastic transport. Mobile dsRNA could transfer to infecting fungi, where it was processed and loaded by the fungal RNAi machinery to elicit gene silencing. Using a novel biochemical purification technique and small RNA sequencing, we detected functional small interfering RNA species derived from foliar-applied dsRNA that elicit effective silencing in both the applied and distal tissue types. Our mechanistic dissection of the uptake and movement of dsRNA provides crucial insights into the mode of action of RNAi biopesticides and stands to add significant benefit to this emerging field of plant protection.