Conserved microRNAs miR-8-5p and miR-2a-3p modulate chitin biosynthesis in response to 20-hydroxyecdysone signaling in the brown planthopper, Nilaparvata lugens.

Molting is an important developmental process in insects, usually along with synthesis and degradation of chitin. 20-hydroxyecdysone (20E), an insect hormone, has been reported to contribute to many processes including molting. However, little is known about the link between the chitin biosynthesis pathway and 20E signaling. Here, we report that conserved miR-8-5p (miR-8-5p) and miR-2a-3p and their new target genes are critical for ecdysone-induced chitin biosynthesis in a hemipteran insect Nilaparvata lugens. We found that membrane-bound trehalase (Tre-2) and phosphoacetylglucosamine mutase (PAGM) in the chitin biosynthesis pathway were targets of miR-8-5p and miR-2a-3p, respectively, through bioinformatic analysis and experimental verification. The levels of miR-8-5p and miR-2a-3p were reduced, whereas the levels of Tre-2 and PAGM were up-regulated in response to 20E. In addition, miR-8-5p and miR-2a-3p were transcriptionally repressed by an early-response gene, the Broad-Complex (BR-C), in the 20E signaling pathway. Moreover, the overexpression of miR-8-5p and miR-2a-3p led to a significant reduction in the survival rate along with a molting obstacles defect phenotype caused by miR-2a-3p mimics feeding, and the chitin content of N. lugens was simultaneously reduced. Thus, miR-8-5p and miR-2a-3p act as molecular link that tune the chitin biosynthesis pathway in response to 20E signaling.