The Direct Interaction between E93 and Kr-h1 Mediated Their Antagonistic Effect on Ovary Development of the Brown Planthopper

The juvenile hormone (JH) signalling and ecdysone signalling pathways are crucial endocrine signalling pathways that orchestrate the metamorphosis of insects. The metamorphic process, the morphological change from the immature to adult forms, is orchestrated by the dramatic reduction of JH and downstream transcription factors. The Kruppel-homologue 1 (Kr-h1), a downstream transcription factor of the JH signalling pathway, represses E93 expression with an anti-metamorphic effect. However, the biochemical interaction between Kr-h1 and E93 and how the interaction regulates ovary development, a sensitive readout for endocrine regulation, remain unknown. In brown planthopper, Nilaparvata lugens, we found that the downregulation of Kr-h1 partially recovered the deteriorating effect of E93 knock-down on metamorphosis. Dual knock down of E93 and Kr-h1 increased ovary development and the number of eggs laid when compared to the effects of the knock down of E93 alone, indicating that the knock down of Kr-h1 partially recovered the deteriorating effect of the E93 knock-down on ovary development. In summary, our results indicated that E93 and Kr-h1 have antagonistic effects on regulating metamorphosis and ovary development. We tested the biochemical interaction between these two proteins and found that these molecules interact directly. Kr-h1 V and E93 II undergo strong and specific interactions, indicating that the potential interacting domain may be located in these two regions. We inferred that the nuclear receptor interaction motif (NR-box) and helix-turn-helix DNA binding motifs of the pipsqueak family (RHF1) are candidate domains responsible for the protein-protein interaction between E93 and Kr-h1. Moreover, the HA-tagged E93 and FLAG-tagged Kr-h1 were co-localized in the nucleus, and the expression of E93 was increased when Kr-h1 was downregulated, supporting that these two proteins may interact antagonistically. JH and ecdysone signalling are critical for the control of ovary development and pest populations. Our result is important for understanding the interactions between E93 and related proteins, which makes it possible to identify potential targets and develop new pesticides for pest management.