Laodelphax striatellus salivary sheath protein Lsactin triggers defense response in plants.

Herbivore-associated molecular patterns (HAMPs) in saliva enable plants to detect herbivores and activate pattern-triggered immunity (PTI). Piercing-sucking herbivores secrete gel-like saliva that forms salivary sheaths, which aid in feeding. However, the role of proteins within these sheaths in modulating plant defenses remains poorly understood. In this study, we identified a thermostable HAMP, actin-related protein 1 (Lsactin), from the salivary sheath of the small brown planthopper (SBPH) Laodelphax striatellus. Lsactin is a widely conserved arthropod protein that serves as an inducer of the BAK1-dependent PTI response in Nicotiana benthamiana, thereby enhancing its resistance to both Bemisia tabaci and Spodoptera frugiperda. Moreover, this HAMP can also induce cell death in plants such as eggplant, cotton, pepper, and corn. Plants were able to specifically recognize the Lsactin 41-amino-acid peptide (LP41), which functions as a minimal immunogenic epitope. Furthermore, LP41 stimulates the production of jasmonic acid and hydrogen peroxide in rice, enhancing rice's resistance to the SBPH. However, silencing Lsactin in SBPH led to the disruption of salivary sheath formation, which reduced insect feeding efficiency. This study demonstrates that Lsactin from the SBPH salivary sheath serves as a crucial HAMP, triggering plants resistance to various insect species.