Investigating a role for piRNA-associated piwi genes in overcoming host-plant resistance in the soybean aphid, Aphis glycines

Authors: HALLER, ANGEL - The Ohio State University; POELSTRA, JELMER - The Ohio State University; PIPATPONGPINYO, WIRAT - The Ohio State University; KREUTER, NATHAN - The Ohio State University; Wilson, Jennifer; MICHEL, ANDREW - The Ohio State University

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2025
Publication Date: 6/5/2025
Citation: Haller, A., Poelstra, J., Pipatpongpinyo, W., Kreuter, N., Wilson, J.R., Michel, A. 2025. Investigating a role for piRNA-associated piwi genes in overcoming host-plant resistance in the soybean aphid, Aphis glycines. Journal of Insect Science. 25(3). Article 18 ieaf055. https://doi.org/10.1093/jisesa/ieaf055.
DOI: https://doi.org/10.1093/jisesa/ieaf055

Interpretive Summary: The soybean aphid, Aphis glycines, is an invasive pest of soybean and vector of many plant viruses that has caused significant damage to soybean crops in the Midwest since its arrival in 2007. The main management strategy used to control the aphid is host plant resistance, the use of soybean varieties with resistance to soybean aphid. However, the aphids are continually evolving to overcome this resistance. Here we endeavored to better understand how this resistance breaking evolves, so we examined a particular small RNA regulatory pathway in the soybean aphid – the piwi-interacting RNA (piRNA) pathway that has previously been implicated in insect adaptation. Piwi proteins bind the piRNA and then silence genes that have sequences matching the piRNA. We performed phylogenetic analysis looking at the number of piwi genes and the evolutionary relationships between them and saw great expansion in PIWI proteins among aphid species as compared to other insects. More closely examining the expression of these Piwi proteins in soybean aphid, we determined that two of them were more highly expressed in resistance-breaking aphids compared to susceptible aphids. These data suggest a functional role of the PIWI proteins and piRNA pathway in aphid adaptation to host plant resistance. Understanding these mechanisms further can help us develop biomarkers to identify resistance-breaking aphids in the field and technologies such as RNAi to stop resistance-breaking in the soybean aphid, allowing farmers to continue to use host plant resistance as a management strategy.

Technical Abstract: Natural host plant resistance provides a sustainable solution to control insect outbreaks but can be limited due to insect counter-adaptation. However, the exact mechanisms of insect adaptation to host-plant resistance remain unclear in most systems. Some insect adaptations are controlled by epigenetic mechanisms, such as through non-coding RNA (ncRNA). PIWI-interacting RNAs (piRNAs) are specific ncRNAs that interact with PIWI proteins to control a diverse range of gene regulatory functions, particularly in insects. Previous investigation into aphid PIWI gene copies showed expansion in their abundance compared to other insects, which may suggest PIWI genes have additional functions among aphids. We first characterized PIWI gene evolution through a phylogenetic analysis, then investigated the role of PIWIs by examining gene expression in the soybean aphid (Aphis glycines), a significant insect pest of soybean which has adapted to overcome aphid-resistance in host plants. Our data indicated the presence of 3 PIWI ortholog groups, as well as taxon-specific gene expansions, with gene copy numbers ranging from 3-17 across species. To evaluate a potential role of PIWIs in overcoming host plant resistance, we measured their gene expression in Ap. glycines with (virulent) and without (avirulent) the ability to survive on aphid-resistant soybean. We found that virulent Ap. glycines have significantly higher expression of two PIWI genes (Agl1.1 and Agl1.3) compared to the avirulent biotype. These data suggest that gene regulatory mechanisms related to the PIWI pathway, potentially including piRNAs, are important in aphid systems and may enable adaptation to host-plant resistance.