RNAi as a Foliar Spray: Efficiency and Challenges to Field Applications

Abstract

RNA interference (RNAi) is a powerful tool that is being increasingly utilized for crop protection against viruses, fungal pathogens, and insect pests. The non-transgenic approach of spray-induced gene silencing (SIGS), which relies on spray application of double-stranded RNA (dsRNA) to induce RNAi, has come to prominence due to its safety and environmental benefits in addition to its wide host range and high target specificity. However, along with promising results in recent studies, several factors limiting SIGS RNAi efficiency have been recognized in insects and plants. While sprayed dsRNA on the plant surface can produce a robust RNAi response in some chewing insects, plant uptake and systemic movement of dsRNA is required for delivery to many other target organisms. For example, pests such as sucking insects require the presence of dsRNA in vascular tissues, while many fungal pathogens are predominately located in internal plant tissues. Investigating the mechanisms by which sprayed dsRNA enters and moves through plant tissues and understanding the barriers that may hinder this process are essential for developing efficient ways to deliver dsRNA into plant systems. In this review, we assess current knowledge of the plant foliar and cellular uptake of dsRNA molecules. We will also identify major barriers to uptake, including leaf morphological features as well as environmental factors, and address methods to overcome these barriers.

Current Scenario of Exogenously Induced RNAi for Lepidopteran Agricultural Pest Control: From dsRNA Design to Topical Application

“…Foliar application is a very practical and convenient SIGS method that has been reducing in cost over time [161]. Reliable dsRNA market products must present convincing low-cost and high-efficiency characteristics.…”

“…Another factor that makes RNAi a difficult strategy to be applied is the uptake of the product when applied via foliar spray. Many leaf surfaces are re-covered, mostly by wax, or have a hydrophobic cuticle, which makes absorption more difficult; the presence of trichomes and stomata density and position also interfere directly with the dsRNA absorption by the plants [161].…”

Current Scenario of Exogenously Induced RNAi for Lepidopteran Agricultural Pest Control: From dsRNA Design to Topical Application

“…dsRNA is a great resource to become a powerful tool for pest control of field crops. To become a true and useful product in the market, the foliar spray is one of the most efficient delivery methods because, with time, it became a low-cost production way and a very practical and convenient application method [167]. Trunk injection is another application method that can be especially useful to be applied in the field, in particular for those crops that are perennial plants and those that present woody trunks, such as citrus, coffee, and pine, among others [50].…”

“…Another factor that makes RNAi a difficult strategy to be applied is the uptake of the product when applied via foliar spray. Many leaves are recovered by any kind of cover, most of them are recovered by some wax or, in some cases, the leaf has a hydrophobic cuticle, which makes the absorption more difficult, also the presence of trichomes and stomata density and position interfere directly on the dsRNA absorption by the plants [167].…”

Clay nanoparticles efficiently deliver small interfering RNA to intact plant leaf cells

“…These methods include the use of Agrobacterium tumefaciens -based, viral-based transformation systems, and biolistic gene guns, and direct leaf spray specifically for the delivery of dsRNA or siRNA. Given that (1) Agrobacterium and viral transformation systems are species dependent and restricted to the transfer of DNA, (2) damages often occur to the plant tissues, cells, and genome after biolistic bombardment, (3) the biomolecule cargos are fragile and easily denatured, and (4) effective delivery of biomolecules to subcellular structures may be required, there is a need for more feasible, benign, biocompatible, and universal delivery approaches ( Cunningham et al, 2018 ; Liu et al, 2019 ; Wang et al, 2019 ; Torti et al, 2021 ; Hoang et al, 2022 ; Uslu et al, 2022 ).…”