Reactive oxygen species (ROS), which comprise superoxide anion, hydrogen peroxide, nitric oxide, and the hydroxyl radical, are by-products of the metabolic activities of aerobic organisms. ROS damage can cause protein oxidation, lipid peroxidation, DNA base alterations, and strand breakage in all major types of biological macromolecules (Limauro et al., 2006). To combat ROS stress, aerobic species have evolved a range of antioxidant defense systems, including dismutases, superoxide peroxidases, catalases, glutathione, and thioredoxin, to protect (Storz and Imlayt, 1999). Peroxiredoxins (Prxs) are a broad family of antioxidant proteins in prokaryotic and eukaryotic organisms. Prxs can potentially remove hydroperoxide by employing thioredoxin as an immediate hydrogen donor (Rhee et al., 2005).

Prxs are enzymatic antioxidants in both intracellular and extracellular environments and play biological roles in cellular signaling, stress regulation, and host immune protection (Rhee et al., 2005, Hambarde et al., 2013, Yu et al., 2011). They are also known as thioredoxin peroxidases (Tpxs) and alkyl-hydroperoxide-reductase-C22 proteins, have aroused the interest of researchers in recent years as a new and increasing family of thiol-specific antioxidant proteins (Wood et al., 2003a). So far, Prxs genes have been identified from various species of insects, including Spodoptera frugiperda, Apis cerana cerana, Bombyx mori, Bombus taurus, and Drosophila melanogaster (Hambarde et al., 2010, Hambarde et al., 2013, Yu et al., 2011, Shi et al., 2012, Radyuk et al., 2001). D. melanogaster has five Prxs genes, three of which are 2-Cys and two 1-Cys. Prxs of all types from D. melanogaster have been discovered to be oxidant defense enzymes with normal peroxidase activity (Radyuk et al., 2001). The first peroxidase found in Saccharomyces cerevisiae is Prxs, a 25-kDa antioxidant enzyme that required thioredoxin as the initial hydrogen donor. Three previously identified TPxs in D. melanogaster have distinct subcellular localization and expression patterns. The three 2-Cys TPxs were found to be active in the thioredoxin system and to reduce H2O2 in the presence of dithiothreitol. TPxs are thought to be particularly important in the enzymatic elimination of ROS. It was discovered in a recent in vitro study on the functional importance of TPxs in D. melanogaster that the transfected S2 cells that overexpressed TPx were more resistant to oxidative stress than the control cell line (Radyuk et al., 2001). The peroxide substrate is responsible for the oxidation of sulfenic acid to an active site cysteine, and this essential catalytic mechanism is shared by all Prxs. In contrast to the 1-Cys subfamily, the 2-Cys, unlike has a second conserved resolving Cys residue in the C-terminus (Wood et al., 2003b, Zhang et al., 2009, Noguera-Mazon et al., 2006, Radyuk et al., 2001).

In animals, members of the Prx family can regulate a variety of physiological processes (Abbas et al., 2019). The functional and biochemical research on members of the Prxs family that have been conducted in insects is, however, still in its early stages. Therefore, we carried out the present study to gain an understanding of the functional role that genes belonging to the Prx family play in insects, in particular in A. pernyi. The functional roles of ApPrx-1 in A. pernyi were investigated for the first time in this study. A. pernyi is a commercially important species of silkworm that is widely cultured in Asia for the production of silk, protein-rich food, and Chinese traditional medicines (Wang et al., 2018). Since A. pernyi is a wild species, it is more susceptible to being affected by microbial pathogens. A. pernyi has evolved an effective immune mechanism that allows it to combat such a potentially harmful pathogen to be resistant to microbial infections (An et al., 2011). There are several lines of evidence that ROS may contribute to the immune responses of insects against pathogens such as fungi and parasites (Altincicek et al., 2012, Schmidt et al., 2001). Keeping this in mind we designed and performed this study to gain a better understanding of the biological role that ApPrx-1 plays in addressing ROS and immune functions.