Insulin-like peptides and DNA/tRNA methyltransferases are involved in the nutritional regulation of female reproduction in Nilaparvata lugens (Stal)

Insulin-like peptides (ILPs) sense and transduce nutritional information and are linked to female reproduction in many insect species. Our previous studies have shown that Target of rapamycin (TOR) pathway functions through juvenile hormone (JH) to regulate amino acids-mediated vitellogenesis in the brown planthopper, Nilaparvata lugens, one of the most destructive rice pests in Asia. Recent reports have demonstrated that DNA methyltransferases (Dnmts) are also involved in female reproduction of N. lugens. However, the roles of ILPs and Dnmts in the nutritional regulation of female reproduction have not been fully elucidated. ILPs and Dnmts are highly expressed in the adult females after a supplement of amino acids, indicating nutrition -stimulated expression patterns of these genes. RNA interference-mediated depletion of NIILP2 or NIILP4 dramatically decreased the expression levels of N1Druntl and N1Dnmt2 (tRNA methyltransferase), and resulted in severely impaired ovary growth as well as the substantial reduction of fecundity. Notably, NIILP2 or NIIIP4 knockdown led to reduced mRNA accumulation of S6 kinase (S6K), a downstream target of the nutritional TOR pathway, and decreased vitellogenin content in the fat body. Silencing NlDnmtl or N1Dnmt2 effectively suppressed ovary development and decreased female fecundity. However, NlDnmtl or N1Dnmt2 knockdown did not influence the expression of NIILP2 and N1ILP4. We infer that amino acids act on ILPs and Dnmts to regulate vitellogenesis and oocyte maturation in N. lugens.