Inhibitory activity of carbon quantum dots against Phytophthora infestans and fungal plant pathogens and their effect on dsRNA-induced gene silencing

Carbon quantum dots (CQDs) have many potential applications due to their cell-penetrating ability, biocompatibility and tunable properties. Among a variety of characteristics, the inhibition of bacteria by CQDs is often reported. However, the effect on other microorganisms, such as plant pathogenic fungi and oomycetes, is poorly studied. Here we monitored the growth of the oomycete plant pathogen Phytophthora infestans in the presence of CQDs, as well as of another three fungal plant pathogens, namely Botrytis cinerea, Alternaria alternata and Fusarium oxysporum. Moreover, the ability of CQDs to improve gene silencing caused by exogenous dsRNA in P. infestans was studied, and the toxicity of CQDs to human keratinocytes was evaluated. Our results indicate significant inhibitory activity of CQDs against P. infestans at relatively low concentrations. In a species-specific manner and to a lesser extent, the growth of the three fungal plant pathogens was also affected. We also found that the treatment of P. infestans with naked dsRNA in vitro did not trigger gene silencing. However, the mixture of CQDs with dsRNA increased RNAi efficiency, by causing a significant reduction of the transcript levels of the target gene in developing sporangia. Finally, no cytotoxicity of the CQDs, in the concentrations active against the plant pathogens, was found.