Abstract: 【Aim】To explore the function of nuclear receptor ultraspiracle protein (USP) in the molting development of Sogatella furcifera nymph and its regulatory relationship with chitin synthesis and degradation. 【Methods】Based on the genome data of S. furcifera, the full-length cDNA sequence of SfUSP was amplified by RT-PCR. The expression levels of SfUSP in different developmental stages (1st-5th instar nymphs, 5th instar nymph prior to ecdysis, 5th instar nymph during ecdysis and female adult), tissues (head, integument, fat body, gut and leg) of the 5th instar nymph, female adult tissues (integument, wing, fat body, leg and ovary) and the day-1 5th instar nymph of S. furcifera after treatment with 100 ng/individual of 20E were detected by RT-qPCR. After the targeted silencing of SfUSP by microinjection of dsRNA into the day-1 5th instar nymph, the nymphal survival rate was calculated, the lethal phenotype of nymphs was observed and the expression levels of the key genes in chitin synthesis and degradation pathways were determined by RT-qPCR. 【Results】The full-length cDNA sequence of SfUSP (GenBank accession number: ON209396) of S. furcifera was obtained by cloning, with an open reading frame of 1 263 bp in length, encoding 420 amino acids. The predicted molecular weight of SfUSP is 47.27 kD with the theoretical isoelectric point of 7.18. Sequence analysis result showed that SfUSP contains five conserved domains of nuclear receptor family, and DNA-binding domain (DBD) and ligand-binding domain (LBD) are highly conserved. The developmental stage expression profiles showed that SfUSP was highly expressed in the 1st instar nymph, and the 5th instar nymphs prior to ecdysis and female adult. The tissue expression profiles showed that SfUSP was expressed highly in the head, integument, fat body and gut of the 5th instar nymphs, and in the wing, leg and integument of the female adult. In addition, at 12 h after microinjection of 20E (100 ng/individual), the expression level of SfUSP in the 5th instar nymph was significantly increased as compared with that in the control group. After targeted silencing of SfUSP expression, the nymphal survival rate of S. furcifera was significantly reduced compared with the control group (injected with dsGFP) and only 18.01% of that of the control group at 6 d after microinjection of dsRNA, with 51.46% individuals unable to molt successfully. In addition, after targeted silencing of SfUSP expression, the expression levels of the key genes SfCHS1, SfCHS1a, SfUAP and SfGFAT in chitin synthesis pathways and SfCht7, SfNAG1, SfNAG2, SfCDA1, SfCDA2 and SfCDA4 in chitin degradation pathways were significantly inhibited, but those of SfG6PI and SfCht10 were significantly increased as compared with those in the control group microinjected with dsGFP. 【Conclusion】SfUSP is a key gene in the growth and development of S. furcifera, which can affect the synthesis and degradation of chitin, and then regulates the ecdysis development of S. furcifera.

Key words: Sogatella furcifera, ultraspiracle protein, molting hormone, chitin synthesis and degradation, ecdysis