# Differential Antioxidant Enzyme Gene Expression and Functional Analysis of Pyridaben-Susceptible and -Resistant Strains of Tetranychus truncatus (Acari: Tetranychidae) under High Temperature Stress

## TL;DR

This study explores how a spider mite species adapts to high temperatures and pesticide resistance by analyzing antioxidant enzyme genes.

## Contribution

The study identifies specific antioxidant enzyme genes involved in thermal adaptation of a pesticide-resistant spider mite strain.

## Key findings

- Four antioxidant enzyme genes (TtSOD, TtPOD3, TtPOD4, TtGSTs2) were found to be differentially expressed in resistant and susceptible spider mite strains under high temperature stress.
- RNA interference showed that silencing the TtPOD4 gene significantly increased mortality in resistant mites under high temperature.
- Resistant mites exhibited higher antioxidant gene expression levels in the adult stage compared to susceptible ones.

## Abstract

Tetranychus truncatus (Acari: Tetranychidae) is the dominant pest on many crops in China. The resistant strain cultivated by pyridaben in our laboratory showed higher adaptability to high temperature than the susceptible strain. Antioxidant enzymes can reduce the damage of reactive oxygen species (ROS) caused by high temperature. Therefore, the antioxidant enzyme genes of T. truncatus were screened, and their biological information was analyzed. The expression patterns of antioxidant enzyme genes in two strains of T. truncatus under high temperature stress were determined by RT-qPCR method, and their functions were verified by RNA interference (RNAi) technology. The experimental results provide a theoretical basis for understanding the occurrence of agricultural mites under the background of climate warming and applying gene regulation technology to control T. truncatus in the future.

Tetranychus truncatus (Acari: Tetranychidae) has caused serious economic losses on some crops (soybean, corn, and cotton) in China, and has developed resistance to most acaricides. Our laboratory study found that T. truncatus was resistant to pyridaben and also adapted to high temperature (34–40 °C). High temperature stress may cause arthropods to produce a large amount of reactive oxygen species (ROS), causing oxidative damage. Antioxidant enzymes, as the main antioxidants, can reduce the damage caused by excessive ROS in arthropods. In order to study the adaptation mechanism of the pyridaben-resistant strain of T. truncatus to high temperature and the role of antioxidant enzyme genes under high temperature stress, four antioxidant enzyme genes, TtSOD, TtPOD3, TtPOD4, and TtGSTs2, were screened according to the transcriptome sequencing data of pyridaben-susceptible and -resistant strains in T. truncatus. Firstly, the phylogeny and structure analyses of these four genes were carried out. Then, real-time quantitative PCR (RT-qPCR) technology was used to analyze the gene expression patterns of antioxidant enzymes in two strains of T. truncatus at three different high temperature ranges (34 °C, 38 °C, and 42 °C). The results showed that the expression levels of four antioxidant enzyme genes of two strains of T. truncatus were induced by high temperature stress, and the expression levels of antioxidant enzyme genes were significantly different in each development state. The gene expression of antioxidant enzyme genes in resistant strains at the adult stage was significantly higher than that in susceptible strains. After the TtSOD and TtPOD4 genes of adult mites of the resistant strain were silenced by RNA interference (RNAi) technology, the mortality rate of mites with TtPOD4 gene silencing reached 41.11% after 96 h at 34 °C, which was significantly higher than that of the control and TtSOD gene silencing. It has been confirmed that the TtPOD4 gene plays a key role in the adaptation of pyridaben-resistant strain of T. truncatus to high temperature. It lays a theoretical foundation for revealing the thermal adaptation mechanism of T. truncatus.