Abstract
Metamorphosis is a crucial process in insect development. Ecdysone-induced protein 93 (E93) is a determinant that promotes adult metamorphosis in both hemimetabolous and holometabolous insects. Krüppel-homolog 1 (Kr-h1), an early juvenile hormone (JH)-inducible gene, participates in JH signaling pathway controlling insect metamorphosis. In the current study, an E93 cDNA (NlE93) and two Kr-h1 cDNA variants (NlKr-h1-a and NlKr-h1-b) were cloned from Nilaparvata lugens (Stål), one of the most destructive hemimetabolous insect pests on rice. Multiple sequence alignment showed that both NlE93 and NlKr-h1 share high identity with their orthologs from other insects. The expression patterns revealed that decreasing NlKr-h1 mRNA levels were correlated with increasing NlE93 mRNA levels and vice versa. Moreover, RNA interference (RNAi) assays showed that the knockdown of one of the two genes resulted in significantly upregulated expression of the other. Correspondingly, phenotypical observation of the RNAi insects revealed that depletion of NlE93 prevented nymph–adult transition (causing a supernumerary nymphal instar), while depletion of NlKr-h1 triggered precocious formation of incomplete adult features. The results suggest that Nlkr-h1 and NlE93 are mutual repressors, fitting into the MEKRE93 pathway. The balance between these two genes plays a critical role in the metamorphosis of N. lugens determining the proper timing for activating metamorphosis during the nymphal stage.
Highlights
The brown planthopper, Nilaparvata lugens (Stål), is one of the most destructive pests in rice
Based on the published N. lugens genome and transcriptome (Xue et al, 2014; Wan et al, 2015), Ecdysone-induced protein 93 (E93) and Krüppel-homolog 1 (Kr-h1) homologs were identified and their sequences were confirmed by reverse transcription polymerase chain reaction (RT-PCR) using primers listed in Supplementary Table S1
The cDNA of E93 gene in N. lugens was cloned and sequenced, and the sequence was submitted to GenBank (KU194468)
Summary
The brown planthopper, Nilaparvata lugens (Stål), is one of the most destructive pests in rice. As a typical hemimetabolous insect, N. lugens undergoes four immature molts of the five nymphal instars, followed by a nymph–adult metamorphic molt to adults with wings and external genitals for reproduction. These processes are controlled by two important hormones, juvenile hormone (JH) and ecdysone (E) (Jindra et al, 2013). Previous studies showed that Krüppel homolog 1 (Kr-h1) was involved in the JH anti-metamorphic action in hemimetabolous insects as an important JH transducer
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