Nanoparticle-delivered RNAi-based pesticide target screening for the rice pest white-backed planthopper and risk assessment for a natural predator

Authors: MA, YUN-FENG - Guizhou University; ZHAO, YA-QIN - Guizhou University; FENG, HONG-YAN - Guizhou University; GONG, LANG-LANG - Guizhou University; ZHANG, MENG-QI - Guizhou University; SMAGGHE, GUY - Guizhou University; Hull, Joe; DEWER, YOUSSEF - Agricultural Research Center Of Egypt; HE, MING - Guizhou University; HE, PENG - Guizhou University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2024
Publication Date: 4/4/2024
Citation: Ma, Y., Zhao, Y., Feng, H., Gong, L., Zhang, M., Smagghe, G., Hull, J.J., Dewer, Y., He, M., He, P. 2024. Nanoparticle-delivered RNAi-based pesticide target screening for the rice pest white-backed planthopper and risk assessment for a natural predator. Science of the Total Environment. 926. Article 171286. https://doi.org/10.1016/j.scitotenv.2024.171286.
DOI: https://doi.org/10.1016/j.scitotenv.2024.171286

Interpretive Summary: RNA interference (RNAi), a cellular mechanism for regulating gene expression, has been developed as a tool for assessing in vivo gene functionality and, more recently, has been proposed as an alternative to chemical-based insect pest management. Despite this interest, wide-spread adoption of the technique has been limited by inefficient delivery of the RNAi triggering agents [e.g. double-stranded RNAs (dsRNAs) that are homologous to the target genes] and identification of suitable candidate genes. The utilization of sprayable formulations that incorporate nanoparticles as dsRNA carriers/protectants has shown promise as an efficient delivery system for some species. Similarly, a number of essential genes that are typically well-conserved across species have been reported to be ideal target genes. Among the genes proposed is a highly conserved proton pump that is essential for cellular function. The pump is composed of multiple subunits, however, not all of the subunits have been fully characterized and their usefulness for insect pest management via targeted disruption remains to be determined. Using sprayable dsRNAs encapsulated by a specific class of nanoparticles, the role of the subunits in insect growth and development was evaluated in the white-backed planthopper, a common pest of rice. Knockdown of two of the subunits resulted in higher incidences of mortality and developmental defects. Application of the nanoparticle carriers targeting the two subunits had no effects on an unrelated insect typically used for biocontrol of white-backed planthopper, suggesting that the two subunits may be useful for pest management. These targets and the sprayable delivery system provide insights that can be further developed for larger scale planthopper control.

Technical Abstract: Vacuolar-type (H+)-ATPase (vATPase) is a conserved multi-subunit eukaryotic enzyme composed of 14 subunits that form a functional complex consisting of an ATP-hydrolytic domain (V1) and a proton-translocation domain (V0). ATP hydrolysis and subsequent H+ translocation rely heavily on a fully assembled V1/V0 complex. Since vATPase is crucial for insect survival, it is a viable molecular target for pest control. However, detailed functional analyses of the 14 subunits and their suitability for pest control have not been fully explored in a single insect species. In this study, we identified 22 vATPase subunit transcripts corresponding to 13 subunits (A1, A2, B, C, D, E, F, G, H, a1, a2, c and d) in the white-backed planthopper (WBPH), Sogatella furcifera, a major hemipteran pest of rice. RNAi screens using microinjection and spray-based methods revealed that the SfVHA-F, SfVHA-a2, and SfVHA-c2 subunits are critical. Furthermore, star polymer (SPc) nanoparticles were utilized to conduct spray-induced and nanoparticle-delivered gene silencing (SI-NDGS) to evaluate the pest control efficacy of RNAi targeting the SfVHA-F, SfVHA-a2, and SfVHA-c2 transcripts. Target mRNA levels and vATPase enzymatic activity were both reduced. Honeydew excreta was likewise reduced in WBPH treated with dsRNAs targeting SfVHA-F, SfVHA-a2, and SfVHA-c2. To assess the environmental safety of the nanoparticle-wrapped dsRNAs, Cyrtorhinus lividipennis Reuter, a major natural enemy of rice planthoppers, was also sprayed with dsRNAs targeting SfVHA-F, SfVHA-a2, and SfVHA-c2. Post-spray effects of dsSfVHA-a2 and dsSfVHA-c2 on C. lividipennis were innocuous. This study identifies SfVHA-a2 and SfVHA-c2 as two promising targets for biorational control of WBPH and lays the groundwork for developing biosafe RNAi biopesticides.