MicroRNA novel-miR-90-5p modulates larval molt development in Ostrinia furnacalis (Guenée) by targeting OfCYP18A1.

The hormone 20-hydroxyecdysone (20E) plays an important role in the physiological processes of insect growth, development, and ecdysis, whereas CYP18A1, a 20E hydroxylase, participates in 20E degradation and maintains its equilibrium state, which is an indispensable part of the 20E signaling pathway. MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression and mediate various biological processes. However, whether and how miRNAs regulate CYP18A1 remains unclear. Herein, OfCYP18A1 was expressed in different developmental stages and tissues. After OfCYP18A1 knockdown, the survival and ecdysis rates of larvae as well as their body weight and length significantly decreased, causing the larvae to molt early but not completely, resulting in death. The concentration of 20E in larvae significantly increased, whereas that of juvenile hormone (JH) significantly decreased. To further investigate the regulatory mechanism of OfCYP18A1, an miRNA (novel-miR-90-5p) targeting OfCYP18A1 was proposed. Novel-miR-90-5p was expressed in different developmental stages and tissues of Ostrinia furnacalis, and it exhibited an inverse trend to OfCYP18A1. Novel-miR-90-5p overexpression in O. furnacalis significantly decreased larval survival and ecdysis rates, delayed their development, decreased the larval body size, increased 20E concentration, and decreased JH concentration. However, after novel-miR-90-5p expression inhibition, the survival rate of 3rd-instar larvae did not significantly differ, their body weight and length significantly increased, ecdysis was delayed, 20E concentration significantly decreased, and JH concentration did not significantly change. These findings reveal that miRNAs are involved in OfCYP18A1 regulation during insect growth and development, thus enhancing our understanding of insect defense strategies.