Abstract
Besides the function of preventing metamorphosis in insects, the juvenile hormone (JH) plays a role in female reproduction; however, the underlying mechanism is largely unknown. The methoprene-tolerant (Met) protein belongs to a family of basic helix-loop-helix–Per-Arnt-Sim (bHLH-PAS) transcription factors and functions as the JH intracellular receptor. In this study, two full length cDNAs encoding Met (CsMet1 and CsMet2) were isolated from the rice stem borer, Chilo suppressalis. Structural analysis revealed that both CsMet1 and CsMet2 exhibited typical bHLH, PAS-A, PAS-B, and PAC (PAS C terminal motif) domains. Comparative analysis of transcript level using reverse transcription-quantitative PCR (RT-qPCR) revealed that CsMet1 was predominant in almost all examined developmental stages and tissues. Treatment with methoprene in vivo induces the transcription of both CsMet1 and CsMet2. Notably, injection of dsCsMet1 and dsCsMet2 suppressed the expression levels of vitellogenin (CsVg) and Vg receptor (CsVgR). These findings revealed the potential JH signaling mechanism regulating C. suppressalis reproduction, and provided evidence that RNAi-mediated knockdown of Met holds great potential as a control strategy of C. suppressalis.
Highlights
The rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is one of the most serious rice pests in Asia, Middle East, and southern Europe, and causes large crop losses through feeding on the stems of rice
The important roles played by juvenile hormone (JH) in insect development and reproduction prompted the study on JH signaling, and the breakthrough had been the identification of transcription factor Met as an intracellular receptor for JH (Charles et al, 2011)
Binding of JH to Met triggers dimerization of Met with another basic helix-loop-helix (bHLH)-PAS protein Taiman (Tai) to form a functional complex, which interacts with JH response elements (JHREs) of target genes (Smykal and Raikhel, 2015)
Summary
The rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is one of the most serious rice pests in Asia, Middle East, and southern Europe, and causes large crop losses through feeding on the stems of rice. In China, the change of cultivation patterns has led to the frequent outbreaks of C. suppressalis in recent years (Mao et al, 2019). To date, spraying chemical insecticides remains the primary strategy for controlling C. suppressalis. Intensive use of insecticides has driven C. suppressalis to develop resistance to a wide range of insecticides (Su et al, 2014; Lu et al, 2017; Yao et al, 2017). The development of RNA interference (RNAi)mediated disruption of reproduction represents an alternative control strategy of C. suppressalis (Miao et al, 2020).
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