NlML1.pdb from An MD-2-related lipid-recognition protein is required for insect reproduction and integument development

The myeloid differentiation factor 2 (MD-2)-related lipid-recognition protein is involved in immune responses through recognizing bacteria lipopolysaccharide in mammals, arthropods and plants. However, the physiological roles of MD-2 in other biological processes are largely unknown. Here, we identified three homologue MD-2 genes (<i>NlML1</i>, <i>NlML2</i> and <i>NlML3</i>) by searching the genome and transcriptome databases of the brown planthopper <i>Nilaparvata lugens</i>, a hemipteran insect species. Temporospatial analysis showed that the <i>NlML1</i> gene was highly expressed in the fat body but lowly expressed in the other tissues, while the <i>NlML2</i> and <i>NlML3</i> genes were highly expressed in the testis or digestive tract. RNA interference-mediated depletion of the <i>NlML1</i> gene significantly downregulated the transcription of numerous integument protein genes. The <i>NlML1</i> knockdown led to moulting failure and mortality at the nymph–adult transition phase, impaired egg laying and hatching and reduced 20-hydroxyecdysone (20E) production in the nymphs. 20E could rescue the deficient moulting phenotypes derived from ds<i>NlML1</i> RNAi. These novel findings indicate that <i>NlML1</i> is required for nymphal moulting and female reproductive success—as it plays an important role in regulating 20E synthesis, lipid and chitin metabolisms in <i>N. lugens</i>—thus contributing to our understanding of developmental and reproductive mechanisms in insects.