Molecular characterization and gene silencing of Laccase 1 in the grain aphid, Sitobion avenae

Laccase 1 (Lac1), a polyphenol oxidase, has been proposed to be involved in insect iron metabolism and immunity responses. However, little information is available on the roles of Lac 1 in insect-plant interactions. The grain aphid Sitobion avenae is one of the most destructive pests of cereal, directly drawing phloem sap and transmitting viruses. In the present study, we first cloned the open reading frame (ORF) of Lac 1 from S. avenae, and the putative protein sequence was predicted to have a carboxyl-terminal transmembrane domain. We found that SaLac 1 had higher expression levels in the fourth and adult stages using reverse transcription real-time quantitative PCR (RT-qPCR). SaLac 1 was highly expressed in the salivary gland and midgut and also in wingless compared with winged morphs. After feeding on aphid-resistant wheat with a high total phenol content, the expression level of SaLac 1 increased significantly. RNA interference (RNAi) by oral feeding successfully inhibited the transcript levels of SaLac 1, and the knockdown of Lac 1 significantly decreased the survival rate of S. avenae on aphid-resistant wheat. Our study demonstrated that S. avenae Lac 1 was involved in the detoxification of phenolic compounds in wheat and was essential for the aphid to adapt to resistant plants.