MicroRNA miR-iab-8 modulates the diapause of Ostrinia furnacalis larvae by targeting the circadian clock gene cycle and affecting the ecdysone signaling pathway

Diapause in insects signifies a critical developmental adjustment to unfavorable seasonal conditions. It involves complex interactions across several signaling pathways, including juvenile hormone, ecdysteroid (20-hydroxyecdysone, 20E), Insulin, circadian clock genes, and MicroRNAs (miRNAs). However, the role of miRNAs and their regulatory circadian genes in diapause and metamorphosis, particularly in the Asian corn borer (Ostrinia furnacalis), remains insufficiently characterized. In this study, a target site of miR-iab-8 was identified in the 3' untranslated region (3'UTR) of OfCycle (OfCyc), and dual-luciferase assays confirmed miR-iab-8-mediated suppression of OfCyc expression in vitro. Similar to the effects of dsRNA targeting the Cycle gene (dsCyc), in vivo administration of miR-iab-8 agomir (a synthetic miRNA agonist that enhances endogenous miRNA activity) to diapausing larvae resulted in inhibition of OfCyc expression, decreased lipid total content, diapause termination, and the development of malformed pupae. However, when miR-iab-8 antagomir (a synthetic miRNA antagonist that inhibits endogenous miRNA function) was administered to non-diapause individuals, it induceddiapause entry, increased larval lipid content, and upregulatedOfCyc expression. Furthermore, exogenous 20E increased the expression of miR-iab-8 and decreased the expression of OfCyc in non-diapause larvae, substantially rescuing the diapause phenotype induced by miR-iab-8 antagomir. This study demonstrated that precise regulation of the cascade expression ofthe 20E/miR-iab-8/Cyc axis is crucial for the development of diapause and metamorphosis in O. furnacalis larvae, thus improving understanding of the molecular mechanisms of MicroRNA target circadian clock gene regulating insect diapause.

20-Hydroxyecdysone; Cycle; Diapause; Ostrinia furnacalis; miR-iab-8.