Developing a nanotechnology solution for treatment of smuts and bunts

Future seed coatings will contain various components including microbes beneficial for the growth and resilience of our crop plants. As we transition to this technology it is imperative that we develop specificity in our treatments where only unwanted microbes are supressed and environmental impacts of treatments are minimized. For use of beneficial fungi in seed coatings, we will have to stop treating seeds with broad-spectrum fungicides. On the Canadian Prairies, this would mean increasing the risk of elevated smut and bunt diseases on cereals. As a solution to this problem we are developing nanocarrier-complexed RNA interference (RNAi) technology that can be tailored to suppress specific fungal pathogens. Smuts and bunts are suitable targets for this technology because they initiate their infection cycle early in seed germination. Seed treatments designed to span this narrow developmental window have a high probability of success and can be applied with relative ease. As a first step towards this goal, we have tested several cell penetrating peptides (CPPs) for their ability to bind double-stranded RNA (dsRNA), the inducer of RNAi. We see different characteristics in binding affinity of CPPs to dsRNA through gel retardation assays and fluorescent dye intercalation. Additionally, we have tested a number of different CPPs for their ability to deliver dsRNA and induce RNAi in basidiospores of Ustilago hordei, the covered smut of barley. Like the differences we observe in gel retardation assays, we also observe selectivity where certain CPPs are effective at delivering into smut cells, while others are not. We will highlight the importance of expanding the utility of seed coatings for suppression of pathogens and for promotion of a healthy rhizosphere.