The involvement of thioredoxin reductase genes in development, reproduction and deltamethrin tolerance in the red flour beetle, Tribolium castaneum

As an essential component of the thioredoxin system, thioredoxin reductase (TrxR) plays an important role in maintaining redox homeostasis in mammalian cells, however, functional characterization of insect TrxRs is still limited. In this study, full-length cDNAs of TcTrxR1 and TcTrxR2 were cloned from the red flour beetle, Tribolium castaneum. Sequence analysis revealed the highly conserved active site motifs CVNVGC and CCS at the N-terminal and C-terminal of TcTrxR1, respectively, whereas TcTrxR2 lacks these two conserved motifs. Analysis of the spatio-temporal expression pattern by RT-qPCR showed that the expression of TcTrxR1 was the highest in 1-day-old larva and brain, and TcTrxR2 was highly expressed in eggs and fat body, respectively. Further functional analysis by RNA interference (RNAi) revealed that knockdown of TcTrxR1 and TcTrxR2 at the larval stage led to 100 % and 98.67 % mortality of larvae beetles, and pupal RNAi of TcTrxR1 and TcTrxR2 resulted in decreased eclosion rates as well as failure of the female adults to lay eggs. Additionally, injection of dsTcTrxR2 decreased the tolerance of beetles to deltamethrin, whereas knockdown of TcTrxR1 significantly increased the tolerance of beetles to deltamethrin. Notably, knockdown of TcTrxR1 significantly upregulated the expression of TcCYP6BQ2, TcCYP6BQ4 and TcCYP6BQ7, and led to nuclear translocation of transcription factor CncC, a major regulator of detoxification in insects. These findings provide insights into the function of insect TrxRs as well as the regulatory mechanisms of CncC, and have applied implications for the RNAi-based insect pest control.