Regulatory Effect of Trehalose Metabolism on Chitin Synthesis in Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) as determined using RNAi

Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is an important pest of crops that causes huge losses to grain production. Trehalose plays an important regulatory role in chitin synthesis. In this study, the mRNA expression of the trehalose synthase (TPS), soluble trehalase (TRE1), and membrane-bound trehalase (TRE2) genes in S. frugiperda were silenced by RNAi to reveal the mechanism by which trehalose metabolism regulates chitin synthesis. The results showed that the survival rate of S. frugiperda at different developmental stages decreased in varying degrees following RNAi, and abnormal phenotypes were detected. TRE1 activity was extremely significantly inhibited after dsTRE1 and dsTRE2 injection, and TRE2 activity was extremely significantly inhibited after dsTPS and dsTRE2 injection. After silencing different trehalose metabolism-related regulatory genes, the trehalose content increased, whereas the glucose content decreased. Chitin synthase A (CHSA) gene was upregulated at 24 h after dsTPS and dsTRE1 injection. CHSA expression was significantly inhibited at 48 h after dsTRE1 injection. Chitin synthase B (CHSB) gene expression was significantly higher at 24 h after dsTRE1 injection. Furthermore, CHSB expression was significantly inhibited at 48 h after dsTPS, dsTRE1, or dsTRE2 injection. RNAi of TRE1 or TRE2 led to a significant decrease in chitin content. The results suggested that inhibiting the mRNA expression of genes related to trehalose metabolism in S. frugiperda could disrupt normal trehalose metabolism, thereby regulating the mRNA expression of downstream chitin synthase genes and further affecting chitin synthesis.