Abstract: 【Aim】 The receptor of juvenile hormone (JH), methoprene-tolerant (Met), activates Krüppel-homolog 1 (Kr-h1), a key transcription factor in JH signaling pathway. Met plays a crucial role in insect metamorphosis. The aim of this study is to explore the functions of NlMet and NlKr-h1 in metamorphosis in the brown planthopper, Nilaparvata lugens. 【Methods】 An opening reading frame (ORF) of NlMet was cloned from N. lugens by PCR. The mRNA expression levels of NlMet and/or NlKr-h 1 were down-regulated by RNAi, and the effects of RNAi on metamorphosis and external genital morphology were observed. 【Results】 The open reading frame of NlMet is 1 185 bp in length, encoding 395 amino acids. The NlMet protein contains four domains, i.e., bHLH, PAS-A, PAS-B and PAC. PAS-B and PAC are highly conserved, whereas the other two show relative lower similarities. By disruption of NlMet and NlKrh-1 expression singly or both in the same time by RNAi in N. lugens, we found that down-regulating NlKr-h 1 in the 4th instar nymphs significantly increased the mortality of nymphs and the newly emerged male and female adults (P<0.05). After interference of NlKr-h 1 in the 5th instar nymphs, only the mortality of nymphs significantly increased (P<0.05), while after interference of NlMet in the 5th instar nymphs, the mortality of nymphs had no significant change (P＞0.05). After interference of both genes, the change tendency of mortality was similar to that after interference of NlKr-h 1. Furthermore, we found that NlKr-h 1 RNAi caused abnormity in female external genitalia. Although we found no visible abnormity of the external genitalia after inference with NlMet, the abnormity rate of the external genitalia increased significantly when both genes were silenced. 【Conclusion】 NlMet cooperates with the downstream transcription factor and has an important role in both metamorphosis and external genitalia development of N. lugens. Our study helps to understand the function of the NlMet and NlKr-h 1 genes in metamorphosis of N. lugens.

Key words: Nilaparvata lugens, metamorphosis, juvenile hormone receptor, JH signaling pathway, RNA interference