Involvement of sensory neuron membrane protein gene (SNMP) in host plant searching in the bird cherry-oat aphid.

Sensory neuron membrane protein (SNMP) gene play a crucial role in insect chemosensory systems. However, the role of SNMP in the host searching behaviour of Rhopalosiphum padi (Hemiptera: Aphididae), a highly destructive pest of cereal crops, has not been clearly understood. Our previous research has shown that three wheat volatile organic compounds (VOCs) - (E)-2-hexenol, linalool, and octanal can attract R. padi, but the involvement of SNMP in the aphid's olfactory response to these wheat VOCs has not to be elucidated. In this study, only one SNMP gene was cloned and characterised from R. padi. The results revealed that the SNMP belongs to the SNMP1 subfamily and was named RpadSNMP1. RpadSNMP11 was predominantly expressed in the antennae of the aphid, with significantly higher expression levels observed in winged forms, indicating that it is involved in olfactory responses of R. padi. RpadSNMP1 expression was significantly up-regulated following starvation, and the expression of this gene showed a decreasing trend after 24 h of aphid feeding. Functional analysis through RpadSNMP1 knockdown demonstrated a significant decrease in R. padi's ability to search for host plants. The residence time of R. padi injected with dsRpadSNMP1 significantly shortened in response to (E)-2-hexenol, linalool and octanal according to the four-arm olfactometer, indicating the crucial role of RpadSNMP1 in mediating the aphid's response to these wheat VOCs. Molecular docking suggested potential binding interactions between RpadSNMP1 and three wheat VOCs. Overall, these findings provided evidence for the involvement of RpadSNMP1 in host plant searching and lay a foundation for developing new methods to control this destructive pest.