A serine-rich salivary protein facilitates brown planthopper feeding and survival by mediating salivary sheath formation.

The piercing-sucking pest, brown planthopper (Nilaparvata lugens, BPH), poses a severe and persistent threat to rice in China and across Asia. During feeding, BPHs secrete salivary proteins to form salivary sheaths, which are crucial for successful and sustained phloem sap ingestion. These salivary sheath proteins are crucial for rice-BPH interactions and hold promise as targets for pest control strategies like RNAi. However, the specific functions of salivary proteins in sheath formation remain largely unclear. In this study, we identify NlSRP, a serine-rich salivary protein in BPH, as a novel planthopper-specific secreted salivary protein. NlSRP is highly expressed in the salivary glands and is delivered into host rice plants during feeding. RNAi-mediated knockdown of NlSRP significantly impairs feeding ability, survival and fecundity of BPH. NlSRP is required for the formation of elongated and branched salivary sheaths in BPH. These results demonstrate that NlSRP plays an essential role in BPH salivary sheath formation, feeding and population growth, advancing our mechanistic understanding of piercing-sucking insect feeding and highlighting its potential as an RNAi-based target for BPH control.