Functionalized Carbon Dot-Delivered RNA Nano Fungicides as Superior Tools to Control Phytophthora Pathogens through Plant RdRP1 Mediated Spray-Induced Gene Silencing

Spray-induced gene silencing (SIGS) represents an attractive avenue for plant protection, but limited uptake efficiency of double-stranded RNA (dsRNA) has restricted its application against the notorious oomycetes, Phytophthora. To control Phytophthora, dsRNAs targeting two essential genes in Phytophthora are screened for their ability to partially decrease Phytophthora capsici (P. capsici) infection and fecundity. To further facilitate SIGS for Phytophthora control, functionalized carbon dots (CDs) are complexed with the screened dsRNAs (dsRNA-CDs) through electrostatic interaction. dsRNA-CDs significantly enhanced the control efficacy of dsRNA against Phytophthora infestans, Phytophthora sojae, and both the wild-type and fungicide-resistant P. capsici. The synergism is based on enhancing dsRNA stability and internalization. Dual treatment with dsRNA-CDs and the corresponding fungicide reduced the amount of fungicide required to achieve the same protective effect by 90%. Plant RdRP1 is the main effector in processing various lengths of small RNAs to induce translation inhibition in Phytophthora. Notably, here the first application of a nano-delivery system to improve the effect of SIGS against Phytophthora pathogens is reported. Moreover, the elucidation of how CD facilitates dsRNA internalization in recipient cell and the molecular mechanism of SIGS can benefit the application of dsRNA-CDs in other plant-pathogen pathosystems through improving dsRNA bioactivity and reducing chemical fungicides application.