Involvement of FTZ-F1 in the regulation of pupation in Leptinotarsa decemlineata (Say).

Abstract During the final instar larvae of holometabolous insects, a pulse of 20-hydroxyecdysone (20E) and a drop in juvenile hormone (JH) trigger larval-pupal metamorphosis. In this study, two LdFTZ-F1 cDNAs ( LdFTZ-F1-1 and LdFTZ-F1-2 ) were cloned in Leptinotarsa decemlineata . Both LdFTZ-F1-1 and LdFTZ-F1-2 were highly expressed just before or right after each molt, similar to the expression pattern of an ecdysteroidogenesis gene LdSHD . Ingestion of an ecdysteroid agonist halofenozide (Hal) enhanced LdFTZ-F1-1 and LdFTZ-F1-2 expression in the final larval instar. Conversely, a decrease in 20E by feeding a double-stranded RNA (dsRNA) against LdSHD repressed the expression. Moreover, Hal rescued the expression levels in LdSHD -silenced larvae. Thus, 20E peaks seem to induce the transcription of LdFTZ-F1 s. Furthermore, ingesting ds LdFTZ-F1 from a common fragment of LdFTZ-F1-1 and LdFTZ-F1-2 successfully knocked down both LdFTZ-F1 s, and impaired pupation. Finally, knocking down LdFTZ-F1 s significantly repressed the transcription of three ecdysteroidogenesis genes, lowered 20E titer, and reduced the expression of two 20E receptor genes. Silencing LdFTZ-F1 s also induced the expression of a JH biosynthesis gene, increased JH titer, but decreased the mRNA level of a JH early-inducible gene. Thus, Ld FTZ-F1s are involved in the regulation of pupation by modulating 20E and JH titers and mediating their signaling pathways.