Abstract
Ovarian development plays an important role in the life history of insects and is crucial for control of the insect population. The metamorphosis of an insect is precisely regulated by the interaction of the juvenile hormone and ecdysone. To understand the role of NlBr and NlKr-h1 in ovary development, we used RNA interference (RNAi) to down-regulate the expression of Broad-Complex (Br) and Krüppel homolog 1 (Kr-h1), two important down-stream transcription factors of juvenile hormone and ecdysone signaling. We further investigated their effects on metamorphosis and ovary development. The results showed that both NlBr and NlKr-h1 are induced by ecdysone. The down-regulation of NlBr and NlKr-h1 alone or together by RNAi is more effective than the topical application of ecdysone on the number of ovarioles, suggesting the necessity of NlBr and NlKr-h1 in determining the number of ovarioles. The ovarian grade was significantly increased/decreased by the topical application of ecdysone and down-regulation of NlBr and NlKr-h1. The pre-oviposition period was also increased. When NlBr and NlKr-h1 were down-regulated together, the ovary grade was not significantly different compared to the control (dsGFP), indicating that the development of the ovary is under the control of both NlBr and NlKr-h1. The interaction between the NlBr and NlKr-h1 on the number of ovarioles and the development of the ovary indicates cross-talk between both juvenile hormone and ecdysone signaling at the transcription level in the brown planthopper. Both genes are nuclear transcription factors and may regulate signaling via down-stream genes. These results would help to both enhance the current understanding of the regulatory mechanism of the interaction between juvenile hormone and ecdysone signaling pathways during ovarian development and to design chemicals to control pests.
Highlights
The growth and development of insects are divided into complete metamorphosis and incomplete metamorphosis
To test whether the downstream factors of juvenile hormone and ecdysone signaling, NlKr-h1 and NlBr are induced by the ecdysteroid treatment, we compared the expression levels of NlBr and NlKr-h1 in brown planthoppers treated by ecdysteroid with the control treated by acetone
Topical application significantly increased the transcriptional level of NlBr and NlKr-h1 after 24 and 48 h of treatment (Figure 1); the reverse responses were observed after 12 h (Figure 1)
Summary
The growth and development of insects are divided into complete metamorphosis and incomplete metamorphosis. Juvenile hormone and ecdysone are two important hormones in the regulation of insect molting and metamorphosis (Jindra et al, 2013; Yamanaka et al, 2013; Belles and Piulachs, 2015). At the end of insect development, the concentration of juvenile hormone decreases, and ecdysone induces the expression of downstream genes, promoting larvae to pupae development (Yamanaka et al, 2007). Ecdysone is a class of steroid hormones mainly produced by the prothoracic glands of the larvae and adult ovaries (Thummel, 2002; Yamanaka et al, 2013; Belles and Piulachs, 2015). The metamorphosis of the insects is precisely regulated by the interaction of juvenile hormone with ecdysone
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