Natural double-stranded RNA mediates plant defence against insect herbivores

RNA interference (RNAi)-based pest control is an eco-friendly alternative to chemical insecticides, yet it remains unclear whether plants have evolved endogenous double-stranded (ds)RNA that induces RNAi in insects for self-defence. Here, we identify a plastidic dsRNA (dsNode343) in oilseed rape that contributes to defence against the cabbage stem flea beetle. Upon feeding, dsNode343 is processed by Dicer-2 into RNA-induced silencing complex (RISC)-associated small interfering (si)RNAs. Degradome signatures support the cleavage of multiple essential beetle transcripts, including cortactin and rpL30 . Dicer-2 inhibition desuppresses these transcripts and increases feeding damage, whereas dsNode343 overexposure reduces damage and survival. Sequence variation in dsNode343 correlates with higher complementarity to beetle transcripts. Orthologous loci in potato and hop generate siRNAs to guide transcript cleavage in their herbivores, suggesting dsNode343 is conserved across plants and exhibits herbivore-associated sequence variation. Our results establish endogenous dsRNA as a mechanistically supported layer of plant defence with implications for insect-resistance breeding.