Antioxidant Enzymes and Heat Shock Protein Genes from Liposcelis bostrychophila Are Involved in Stress Defense upon Heat Shock

SIMPLE SUMMARY: Liposcelis bostrychophila is one of the most serious pests of stored commodities among the psocids. Controlling psocids mainly relies on chemical insecticides and heat stress. In fact, L. bostrychophila has developed high levels of resistance or tolerance to heat treatment in grain storage systems. In this study, we evaluated the changes in malondialdehyde (MDA) concentration after different high temperatures. The result showed that MDA is increased slightly overall, but a drastic increase is detected at 42.5 °C for exposure of different times. To further explore the principles of L. bostrychophila in response to heat stress, we tested the changes of superoxide dismutase (SOD), catalase (CAT), peroxidases (POD) and glutathione-S-transferases (GST) activities under different heat treatments and identified four inducible LbHsp70 genes and one LbHsp110 gene. Enzyme activities and transcript levels changed drastically after different heat treatments. These findings contribute to our understanding of the mechanism of L. bostrychophila responding to heat stress and provide baseline information for further understanding the excellent targets of L. bostrychophila. ABSTRACT: Psocids are a new risk for global food security and safety because they are significant worldwide pests of stored products. Among these psocids, Liposcelis bostrychophila has developed high levels of resistance or tolerance to heat treatment in grain storage systems, and thus has led to investigation of molecular mechanisms underlying heat tolerance in this pest. In this study, the time-related effects of thermal stress treatments at relatively high temperatures on the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-S-transferases (GST) and malondialdehyde (MDA), of L. bostrychophila were determined. Thermal stress resulted that L. bostrychophila had a significantly higher MDA concentration at 42.5 °C, which indicated that the heat stress increased lipid peroxidation (LPO) contents and oxidative stress in this psocid pest. Heat stress also resulted in significant elevation of SOD, CAT and GST activities but decreased POD activity. Our data indicates that different antioxidant enzymes contribute to defense mechanisms, counteracting oxidative damage in varying levels. POD play minor roles in scavenging deleterious LPO, while enhanced SOD, CAT and GST activities in response to thermal stress likely play a more important role against oxidative damage. Here, we firstly identified five LbHsps (four LbHsp70s and one LbHsp110) from psocids, and most of these LbHsps (except LbHsp70-1) are highly expressed at fourth instar nymph and adults, and LbHsp70-1 likely presents as a cognate form of HSP due to its non-significant changes of expression. Most LbHsp70s (except LbHsp70-4) are significantly induced at moderate high temperatures (<40 °C) and decreased at extreme high temperatures (40–45 °C), but LbHsp110-1 can be significantly induced at all high temperatures. Results of this study suggest that the LbHsp70s and LbHsp110 genes are involved in tolerance to thermal stress in L. bostrychophila, and antioxidant enzymes and heat shock proteins may be coordinately involved in the tolerance to thermal stress in psocids.