Cross kingdom RNA trafficking - A novel tool for plant disease management

Small RNAs (sRNAs) are a diverse group of endogenous non-coding RNAs that regulate development, genome stability, and plant responses to biotic and abiotic stresses. Based on their origin and biogenesis, sRNAs are broadly categorized into microRNAs (miRNAs), small interfering RNAs (siRNAs), and secondary siRNAs, each generated through distinct yet partially overlapping pathways involving Dicer-like enzymes, RNA-dependent RNA polymerases, and Argonaute proteins. In addition to acting locally, sRNAs exhibit remarkable mobility: they move between neighboring cells through plasmodesmata and travel systemically via the phloem, thereby coordinating developmental and immune responses. Recent advances have established sRNAs as central players in cross-kingdom communication. Plant pathogens secrete sRNAs as effectors to suppress host defense by targeting immunity-associated transcripts. Conversely, plants can export sRNAs into pathogens to prevent the expression of pathogen virulent genes. Thus, the suppression of virulence genes can diminish the host-pathogen interaction, resulting in reduced pathogenesis in the host plant. These discoveries underpin innovative approaches such as host-induced gene silencing (HIGS) and spray-induced gene silencing (SIGS), which harness sRNA mobility for sustainable crop protection. Moreover, the stability of mobile sRNAs is supported by protective mechanisms such as low RNase activity in phloem sap and potential chemical modifications, including methylation and glycosylation. Beyond pathogens, beneficial microbes and biocontrol agents also engage in sRNA exchange with hosts, influencing immunity and disease outcomes. This review highlights recent progress in understanding sRNA biogenesis, trafficking, and regulatory roles, and emphasizes their promise as a foundation for developing next-generation RNA-based bio-pesticides for sustainable agricultural disease management.