Barrier to bypass: a PEI-functionalized star polycation platform for potent broad-spectrum aphid RNAi management

Star polycation (SPc) has been validated as an efficient RNA delivery carrier, yet its limited RNA-binding capacity, formulation stability and multi-barrier penetration restrict its cost-effective application in sprayable RNA pesticides. Here, we functionalized SPc with polyethyleneimine (PEI) to develop a series of SPcP nanoparticles, rationally integrating SPc’s protective capacity with PEI’s cationic charges and membrane-interactive features. Among synthesized SPcP nanoparticles, SPcP3 formed compact spherical nanocomplexes with dsRNA through electrostatic interactions, hydrogen bonding and Van der Waals forces. Notably, SPcP3 complexation not only markedly enhanced RNA stability against nuclease, thermal and extreme pH challenges, but also significantly improved leaf surface deposition, aphid cuticle penetration and cellular internalization. Transcriptomic profiling in Sf9 cells revealed that the SPcP3-mediated delivery enhancement arose from coordinated activation of endocytosis, vesicle trafficking, lysosome-related processes and transmembrane transport, which was consistent with the proposed “proton sponge” effect and identified a previously unrecognized auxiliary transport route. Leveraging this platform, we screened conserved sequences of ATP-d , CHS and EcR across five aphid species and assembled them into a multi-target shRNA formulation (shRNAs/SPcP3). This formulation achieved stable broad-spectrum control against five aphid species, with laboratory control efficacies of 87.3%–96.9%, while exhibiting excellent biocompatibility-no obvious adverse impacts on cucumber growth, natural enemy Harmonia axyridis or Sf9 cells. Collectively, this study establishes a robust nano-platform that overcomes the major delivery barriers limiting RNA pesticide application, offering a scalable and eco-friendly strategy for broad-spectrum aphid management.