fig1

Figure 1. Cross-kingdom RNAi in plant–microbial interactions. Some fungal pathogens, such as B. cinerea and V. dahlia, deliver sRNAs into the plant cells to silence host genes that are involved in plant immunity^[88,91]. Cross-kingdom RNAi is bidirectional, and plants secrete TET8/9-positive EVs to transport host functional sRNAs into pathogens to silence fungal genes involved in virulence^[29]. TET8/9-positive EVs contain a variety of RBPs, including AGO1, RHs, and ANNs, which contribute to the selection or stabilization of sRNAs in EVs^[56]. Cross-kingdom RNAi also exists in bacteria-plant interaction. Rhizobia tRNA-derived short fragments act as functional sRNAs moving into plant cells to silence target genes related to nodulation^[113]. sRNAs from fungal pathogen and bacterium rhizobia were all found to be loaded into plant host AGO1 to silence host target genes. Fungi and bacteria are predicted to secrete and transport sRNAs into host cells by EVs. The question mark indicates a prediction that has not yet been validated experimentally. EVs: extracellular vesicles; MVB: multivesicular body; ILV: intraluminal vesicle; OM: Outer membrane; PM: plasma membrane; sRNA: small RNA; TE: Transposable element; tRFs: tRNA-derived fragments.