Jasmonic acid, ethylene and ROS are involved in the response of cucumber (Cucumis sativus L.) to aphid infestation

Aphis gossypii Glover (Melon aphid) attack cucumber, and cause great loss of yield and quality. However, the molecular mechanisms of aphid resistance in cucumber remain unclear. Here, we investigated differentially regulated proteins (DRPs) in aphid-infested and non-infested cucumber, using a line (EP6392) that is highly resistant to aphids. Cucumber leaves were subjected to infestation levels of 0, 5 and 20 aphids per cucumber. Fifty-four DRPs were found between the 5 and 0 groups and 109 DRPs were found between the 20 and 0 groups. Sixteen of the up-regulated DRPs and 16 of the down-regulated DRPs were common to both the 5 vs 0 and 20 vs 0 groups. Three genes were up-regulated in both the 5- and 20-aphid-infested plants. These genes encoded 12-oxophytodienoate reductase (OPR), which is involved in jasmonic acid (JA) biosynthesis, 1-aminocyclopropane-1-carboxylic acid oxidase, which is involved in ethylene biosynthesis and peroxidase, which is involved in reactive oxygen species (ROS) formation. Exogenous application of JA decreased the aphid reproduction in cucumber leaves and increased the gene expression level of OPR11. Aphid infestation resulted in rapid increases in the levels of ethylene and ROS. Application of an ethylene receptor inhibitor 1-methylcyclopropene (1-MCP) enhanced aphid reproduction. These results indicate that JA, ethylene and ROS mediate the interaction between aphids and cucumber. The early response of ROS and ethylene might be signaling to regulate the cucumber response to aphid infestation, and JA and ethylene might enhance the aphid resistance in cucumber.