An Insect Salivary Sheath Protein Triggers Plant Resistance to Insects and Pathogens as a Conserved HAMP

Herbivore-associated molecular patterns (HAMPs) in saliva enable plants to detect herbivores and activate pattern-triggered immunity (PTI). Piercing-sucking herbivores secrete gel saliva, forming salivary sheaths that assist in feeding, however, the role of proteins within these sheaths in modulation of plant defenses remains poorly understood. Here, a thermostable HAMP, myosin light chain 1-like (myosin) is identified, from the salivary sheath of the small brown planthopper (SBPH) Laodelphax striatellus. Myosin is a widely conserved arthropod protein, and acts as an elicitor of BAK1-dependent PTI responses in several plant species. Plants are able to specifically recognize the myosin 41-amino-acid peptide (MP41), which acts as a minimal immunogenic epitope. Furthermore, myosin and MP41 stimulate jasmonic acid and H₂O₂ production in rice. The resulting defenses not only diminish planthopper performance directly but also induce volatile emissions, attracting a common parasitoid. Additionally, expression of myosin in rice increased plant resistance to a chewing insect as well as to viral and fungal pathogens. However, silencing myosin in SBPH resulted in disruption of salivary sheath formation, reducing insect feeding efficiency. This study demonstrates that myosin from the SBPH salivary sheath serves as a critical and unavoidable HAMP, triggering broad-spectrum plant resistance to various insects and pathogens.