Aquatic fate of a double‐stranded RNA in a sediment­­–water system following an over‐water application

Abstract

Determining the rate of biodegradation of double-stranded RNA (dsRNA) in the environment is an essential element of a comprehensive risk assessment of an RNA-based agricultural product. This information is used during problem formulation to define relevant routes and durations of environmental exposure for in planta-expressed dsRNA. Although exposure to biotechnology-derived crops expressing dsRNA traits in the aquatic environment is predicted to be minimal, little is known regarding the fate of dsRNA in these environments. To assess exposure to aquatic environments, a study was conducted to measure the rate of biodegradation of DvSnf7 dsRNA in aerobic water-sediment systems. Aquatic systems containing natural water and sediments that varied in physical and chemical characteristics were treated with dsRNA by applying DvSnf7 dsRNA directly to the water column. In the present study, DvSnf7 dsRNA dissipated rapidly from the water phase and was undetectable within 7 d as measured by QuantiGene (Affymetrix) and a sensitive insect bioassay in these diverse systems. Degradation kinetics estimated a half-life (time to 50% dissipation [DT50]) of less than 3 d and a time to 90% dissipation of approximately 4 d. Further analysis indicated that DvSnf7 dsRNA had DT50 values of less than 6 d in both sediment-free systems containing natural water and systems with only sediment. Taken together, the results of the present study indicate that dsRNA-based agricultural products rapidly degrade and consequently are unlikely to persist in aquatic environments. Environ Toxicol Chem 2017;36:727-734. © 2016 SETAC.

Dissipation of double‐stranded RNA in aquatic microcosms

“…Both the insecticidal dsRNA and the non‐insecticidal dsRNA surrogate were undetectable after 32 h . Finally, Fischer et al studied the fate of an insecticidal dsRNA in aquatic microcosm. The authors estimated the half‐life of the dsRNA at less than 3 d, and the time to 90% dissipation at approximately 4 d .…”

RNA Interference for Mosquito and Mosquito-Borne Disease Control

“…Many different delivery approaches have been used for per os RNAi trigger delivery in larvae, including naked dsRNA in buffer or water [126,127]. Although naked dsRNA can be internalized at high concentration in sterile conditions in the lab, dsRNA in field settings could be subject to rapid environmental degradation [21,22]. To prevent RNAi trigger degradation, abiotic and biotic delivery systems including the use of Effectene ® (Qiagen) liposomes, chitosan nanoparticles, E. coli expression systems, and Pichia pastoris expression systems have been explored [27,47,49,75,122,123,128,129].…”

“…In some cases larvae are soaked in large quantities of naked RNAi triggers resulting in suppression of the target after consumption [13,124,126,127]. However the aquatic environment of larvae in the field will inevitably lead to degradation of unprotected RNAi triggers [22]. Additionally the presence of midgut ribonucleases prevents successful RNAi trigger delivery in the desert locust Schistocerca gregaria and the German cockroach B. germanica [72,150].…”

“…For one, biologically produced dsRNA does not need to be expressed in the mosquito and as such does not require transfection or a mosquito specific promoter. Also dsRNA is rapidly degraded in aqueous environments [22]. This concept was originally explored by feeding dsRNA expressing E. coli to C. elegans [38].…”

“…In order to achieve these same detrimental phenotypes in wild populations, RNAi triggers must be delivered to the target species and life stage with consideration for environmental and abiotic factors including: UV, ribonucleases, microbes, dissipation and dilution in aqueous environs and on solid substrates [20,21,22,23]. RNAi triggers must also be delivered to target mosquito species using field feasible applications.…”