Apolygus lucorum effector Al6 promotes insect feeding performance on soybean plants: RNAi analysis and feeding behaviour study with electrical penetration graph.

Abstract

The mirid bug Apolygus lucorum, a dominant mirid species in northern China, is a notorious polyphagous pest with more than 200 hosts, including several major crops such as cotton and soybean, resulting in massive economic loss. Studies of insect salivary effectors may provide a novel control strategy for A. lucorum. An A. lucorum effector, that is, Al6, that inhibits plant immunity by using glutathione peroxidase to repress reactive oxidase accumulation was previously identified. In this study, we further explored the molecular functions of Al6 associated with feeding behaviour and insect survival on soybean, a major host of A. lucorum, using RNA interference and electrical penetration graph (EPG) techniques. We initially observed the injury symptom of this mirid bug and characterized feeding behaviour on soybean leaves using EPG. Our results revealed that A. lucorum preferred to feed on young plant organs such as tender leaves, shoots and buds. This mirid bug used cell rupture as a feeding strategy to ingest cell contents from plant tissues. Subsequently, we silenced the Al6 gene using RNAi and investigated the feeding behaviour, honeydew excretion, body weight, and survival rates of A. lucorum on soybean after Al6 knockdown. Our results demonstrated that silencing of Al6 significantly reduced feeding duration, amount of honeydew secretion, body weight, and survival rates of A. lucorum. Thus, our findings provide a novel molecular target of plant-mediated RNAi for the control of A. lucorum.