Knockdown of the salivary protein gene NlG14 caused displacement of the lateral oviduct secreted components and inhibited ovulation in Nilaparvata lugens

Saliva plays important roles in insect feeding, but its roles in insect reproduction were rarely reported. Here we reported that the knockdown of a salivary gland-specific gene NlG14 disrupted the reproduction through inhibiting the ovulation of the brown planthopper (BPH), Nilaparvata lugens (Stal), one of the most devastating rice pests in Asia. NlG14 knockdown caused the displacement of the lateral oviduct secreted components (LOSC), leading to the ovulation disorder and the accumulation of mature eggs in the ovary. The RNAi-treated females laid much less eggs than their control counterparts, though they had the similar oviposition behavior on rice stems as controls. NlG14 protein was not secreted into the hemolymph, indicating an indirect effect of NlG14 knockdown on BPH reproduction. NlG14 knockdown caused the malformation of A-follicle of the principal gland and affected the underlying endocrine mechanism of salivary glands. NlG14 reduction might promote the secretion of insulin-like peptides NlILP1 and NlILP3 from the brain, which up-regulated the expression of Nllaminin gene and then caused the abnormal contraction of lateral oviduct muscle. Another explanation was NlG14 reduction disrupted the ecdysone biosynthesis and action through the insulin-PI3K-Akt signaling in ovary. Altogether, this study indicated that the salivary gland specific protein NlG14 indirectly mediated BPH ovulation process, which established a connexon in function between insect salivary gland and ovary. Author summarySalivary glands play important roles in the feeding process of animals. The salivary glands of insects can secrete various proteins through the exocrine pathway to help them digest and regulate the defense response of host. The endocrine function of insect salivary glands is rarely reported. We found that decreased expression of the salivary protein gene NlG14 resulted in abnormal contraction of lateral oviduct muscles, thus inhibiting ovulation of the brown planthopper. NlG14 could not be secreted into the haemolymph as an endocrine function, but NlG14 knockdown caused the deformity of salivary gland. The reduction of NlG14 regulated insulin release in the brain and insulin-PI3K-Akt signaling in ovary. The disruption of these signaling pathways caused the abnormal contraction of lateral oviduct muscles, resulting in ovulation disorders. These findings provide a case of salivary gland regulating ovarian reproduction in insects.