Abstract
Efforts to develop more environmentally friendly alternatives to traditional broad-spectrum pesticides in agriculture have recently turned to RNA interference (RNAi) technology. With the built-in, sequence-specific knockdown of gene targets following delivery of double-stranded RNA (dsRNA), RNAi offers the promise of controlling pests and pathogens without adversely affecting non-target species. Significant advances in the efficacy of this technology have been observed in a wide range of species, including many insect pests and fungal pathogens. Two different dsRNA application methods are being developed. First, host induced gene silencing (HIGS) harnesses dsRNA production through the thoughtful and precise engineering of transgenic plants and second, spray induced gene silencing (SIGS) that uses surface applications of a topically applied dsRNA molecule. Regardless of the dsRNA delivery method, one aspect that is critical to the success of RNAi is the ability of the target organism to internalize the dsRNA and take advantage of the host RNAi cellular machinery. The efficiency of dsRNA uptake mechanisms varies across species, and in some uptake is negligible, rendering them effectively resistant to this new generation of control technologies. If RNAi-based methods of control are to be used widely, it is critically important to understand the mechanisms underpinning dsRNA uptake. Understanding dsRNA uptake mechanisms will also provide insight into the design and formulation of dsRNAs for improved delivery and provide clues into the development of potential host resistance to these technologies.
Highlights
Each year, crop pests and pathogens cause approximately 300 billion USD of damage to plant-based food supplies worldwide [1]
Demonstrated that uptake of double-stranded RNA (dsRNA) in Sclerotinia sclerotiorum occurs through clathrin-mediated endocytosis, analogous to insect systems that do not rely on SIL channels (Figure 1)
Complexed with chitosan showed reduced accumulation within these endosomes. While it is unknown if the dsRNA-chitosan conjugate enters through endocytic mechanisms similar to naked dsRNA or through alternative mechanisms, it is highly encouraging that this formulation can improve efficiency in species that were previously insensitive to RNA interference (RNAi)
Summary
Crop pests and pathogens cause approximately 300 billion USD of damage to plant-based food supplies worldwide [1]. This review will explore proposed mechanisms of dsRNA uptake in eukaryotes as a means to control both insect pests and fungal pathogens through RNAi. SIGS provides considerable promise, both in terms of offering a new generation of pesticides that are environmentally more benign than most current pesticides, and in terms of applying RNA technologies in a delivery method that avoids the challenges surrounding the regulation of genetic modification. While recent studies clearly demonstrate the potential of SIGS as a tool to control insect pests and fungal pathogens, we still require a deeper understanding of target species that are sensitive or those refractory to RNAi. The current review updates our understanding of RNAi and provides novel insight into the requirements necessary to develop successful alternatives to exogenously-applied broad-spectrum chemistries. We provide strategies to improve dsRNA uptake through the optimization and development of exogenously-applied dsRNA formulations and delivery methods
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