Abstract: 【Objective】The aim of this study is to clone a serine protease inhibitor gene Nlserpin2 and clarify its expression patterns and biological functions in the brown planthopper (BPH), Nilaparvata lugens.【Method】Based on the transcriptome data of BPH, the full-length cDNA of Nlserpin2 was cloned by PCR, and its nucleotide and protein sequences were subsequently characterized using bioinformatics tools. The expression patterns of Nlserpin2 in different developmental stages, different tissues and in response to an entomopathogenic fungus Metarhizium anisopliae were determined by qRT-PCR. The target gene Nlserpin2 was further silenced by RNAi, and the surviaval rate and the changes in the resistance to the M.anisopliae infection of BPH were determined by bioassay.【Result】The Nlserpin2 (GenBank accession number: KC355239) was successfully cloned from BPH. The open reading frame (ORF) is 1 209 bp in length, encoding 402 amino acids with a conserved serpin domain and a reactive center loop (RCL) that typically existed in the members of the serpin superfamily. A signal peptide consisting of 27 amino acid residues was also predicted at the N-terminus. The phylogenetic analysis showed that Nlserpin2 is clustered together with other hemipteran Nlserpin2, and has the highest homology with Sogatella furcifera serpin. The qRT-PCR results showed that the expression of Nlserpin2 had obvious temporospatial characteristics. The lowest and highest expression levels were observed in the 3rd nymphs and the male adults, respectively. The transcript level of Nlserpin2 in the gut was significantly higher than that in the fat body and ovary. The expression of Nlserpin2 in BPH was significantly upregulated at 2 and 3 days post infection with M. anisopliae. RNAi results showed that the expression levels of Nlserpin2 could be significantly inhibited by microinjection of dsNlserpin2. Inhibition of Nlserpin2 expression caused significantly decreased in the survival rate and the capability to resist M. anisopliae infection of the 5th instar nymphs of BPH. 【Conclusion】Nlserpin2 plays important roles in the growth, development and pathogen defense of BPH, which can be used as a potential target for RNAi-mediated control of BPH and provided the gene of interest for genetic improvement of entomopathogenic fungi with a hypervirulent to BPH.

Key words: Nilaparvata , lugens, serine protease inhibitor,  , spatio-temporal expression, inducible , expression, RNA , interference