Abstract:  【Aim】 The phytophagous piercing-sucking insect saliva protein participates in the regulation of plant defense response against insects and affects insect adaptability to host plants. The aim of the present study is to clone the important salivary protein gene Nl15 in the brown planthopper, Nilaparvata lugens, and to investigate its temporal and spatial expression patterns, so as to clarify its roles in virulence of N. lugens. 【Methods】 Based on the transcriptome data of IR56 population of N. lugens, the cDNA sequence of Nl15 was cloned from N. lugens by RT-PCR, and subjected to bioinformatics analysis. The expression profiles of Nl15 in different developmental stages (egg, 1st-5th instar nymph, and female and male adult) and female adult tissues (head, thorax, abdomen and leg) of TN1 and IR56 populations of N. lugens were determined by qPCR. The RNAi of Nl15 was carried out by dsRNA microinjection into the 4th instar nymphs of TN1 and IR56 populations of N. lugens. The relative expression levels of Nl15 in N. lugens nymphs after RNAi of Nl15 and defense-related genes OsLecRK4, OsMPK10, OsWRKY24, OsLox, OsNPR1, and OsGns5 in rice plants fed by N. lugens nymphs for 3 d following RNAi of Nl15 were detected by qPCR. The survival rate and the honeydew amount and body weight gain of N. lugens adults after RNAi of Nl15 were determined by bioassay. 【Results】 The cDNA sequence of Nl15 (GenBank accession no.: OK181113) of N. lugens was cloned. It has an open reading frame of 1 008 bp in length, encoding 335 amino acids with the predicted isoelectric point of 7.54 and the molecular weight of 38.7 kD. The Nl15 protein contains a signal peptide sequence of 23 aa and a predicted glycosylation modification site, whereas has no transmembrane domain and other known functional domains. Nl15 shares 45% amino acid sequence identity with the homologous protein from Laodelphax striatellus. Developmental expression profile revealed that Nl15 was expressed in various developmental stages of N. lugens, with the highest expression level in the 3rd-4th instar nymphs. Tissue expression profile showed that Nl15 exhibited the highest expression level in the head of female adults of N. lugens, with a higher expression level in the head of IR56 population than in the head of TN1 population. RNAi results showed that the expression level of Nl15 in dsNl15 injection group was significantly down-regulated by 89.5%, the survival rate and the honeydew amount and body weight gain of adults of N. lugens were significantly decreased, and the expression levels of the above six rice defense-related genes were significantly up-regulated as compared to those in the control group (dsGFP injection group). 【Conclusion】 Nl15 in IR56 population of N. lugens is involved in the interaction of defense and counter defense between N. lugens and rice. This study provides insights into the mechanisms by which N. lugens overcomes resistance genes and the molecular network of interactions between insects and plants.

Key words: Nilaparvata lugens, IR56 population; Nl15, RNAi; OsLecRK4, rice defense