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

Sensory neuron membrane protein (<i>SNMP</i>) gene play a crucial role in insect chemosensory systems. However, the role of <i>SNMP</i> in the host searching behaviour of <i>Rhopalosiphum padi</i> (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 <i>R. padi</i>, but the involvement of <i>SNMP</i> 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 <i>R. padi</i>. The results revealed that the SNMP belongs to the SNMP1 subfamily and was named RpadSNMP1. <i>RpadSNMP11</i> 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 <i>R. padi. RpadSNMP1</i> 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 <i>RpadSNMP1</i> knockdown demonstrated a significant decrease in <i>R. padi</i>'s ability to search for host plants. The residence time of <i>R. padi</i> injected with ds<i>RpadSNMP1</i> significantly shortened in response to (E)-2-hexenol, linalool and octanal according to the four-arm olfactometer, indicating the crucial role of <i>RpadSNMP1</i> 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 <i>RpadSNMP1</i> in host plant searching and lay a foundation for developing new methods to control this destructive pest.