Functionalized selenium-doped carbon quantum dots: efficient dsRNA delivery for a rotating attack–defense–restock strategy against Phytophthora diseases

The practical application of double-stranded RNA (dsRNA) in plant disease management is severely constrained by its rapid environmental degradation, limited uptake efficiency, and scarcity of effective targets. In this study, a series of dsRNAs were designed to target PsSTT3A , which encodes the catalytic subunit of the oligosaccharyltransferase complex in Phytophthora sojae. Among them, dsSTT3A-5 exhibited effective inhibitory activity against P. sojae with favorable biosafety profiles. To further improve dsRNA delivery efficiency, chitosan-functionalized selenium-doped carbon quantum dots (SeCQDs-CS) were subsequently developed as a dsRNA nanocarrier. SeCQDs-CS could efficiently bind dsSTT3A-5, protect dsRNA from enzymatic degradation, and facilitate dsRNA uptake in plants, thereby improving RNAi-mediated control of P. sojae in soybean. The dsSTT3A-5@SeCQDs-CS also exhibited broad-spectrum protective activity against P. infestans on potato and P. capsici on tobacco. The dsRNA-mediated RNAi directly “attacks” Phytophthora spp. to suppress their development and infection. Meanwhile, SeCQDs-CS enhanced antioxidant enzyme activities and induced the expression of immune-related genes, enabling activation of host “defense” responses. Additionally, SeCQDs-CS treatment increased selenium, nitrogen and phosphorus accumulation in soybean, representing the nutrient “restock” component. Collectively, this study established dsSTT3A-5@SeCQDs-CS as a multifunctional RNA nanoplatform that integrates pathogen-targeted RNAi, host defense activation, and nutrient supplementation. This coordinated “attack–defense–restock” strategy provides a promising framework for the design and application of high-efficiency RNA nano-fungicides toward sustainable management of Phytophthora diseases.